Stability Manual

Maxsurf Stability Windows Version 20

User Manual

© Bentley Systems, Incorporated 2013

License and Copyright Maxsurf Stability Program & User Manual © 2013 Bentley Systems, Incorporated

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Contents

Contents License and Copyright...................................................................................................... iii Contents .............................................................................................................................. v About this Manual .............................................................................................................. 1 Chapter 1 Introduction........................................................................................................ 3 Input Model .............................................................................................................. 3 Analysis Types ......................................................................................................... 4 Analysis Settings ...................................................................................................... 4 Environment Options ............................................................................................... 4 Stability Criteria ....................................................................................................... 5 Output....................................................................................................................... 5 Chapter 2 Quickstart ........................................................................................................... 7 Upright Hydrostatics Quickstart .............................................................................. 7 Large Angle Stability Quickstart ............................................................................. 8 Equilibrium Condition Quickstart ............................................................................ 9 Specified Condition Quickstart .............................................................................. 10 KN Values Quickstart ............................................................................................ 11 Limiting KG Quickstart ......................................................................................... 11 Floodable Length Quickstart .................................................................................. 12 Longitudinal Strength Quickstart ........................................................................... 13 Tank Calibrations Quickstart ................................................................................. 14 MARPOL Oil Outflow Quickstart ......................................................................... 15 Probabilistic Damage Quickstart............................................................................ 15 Chapter 3 Using Maxsurf Stability ................................................................................... 16 Getting Started ....................................................................................................... 16 Installing Maxsurf Stability ......................................................................... 16 Starting Maxsurf Stability ............................................................................ 16 Maxsurf Stability Model ........................................................................................ 17 Preparing a Design in Maxsurf .................................................................... 18 Opening a New Design ................................................................................ 25 Opening an Existing Maxsurf Stability Design File .................................... 26 Effect of Zero Point change ......................................................................... 27 Updating the Maxsurf Stability Model ........................................................ 30 Maxsurf Stability Sections Forming ............................................................ 31 Checking the Maxsurf Stability model ........................................................ 34 Setting Initial Conditions ............................................................................. 38 Working with Loadcases.............................................................................. 43 Auto ballasting ............................................................................................. 56 Modelling Compartments ............................................................................ 59 Tank sections ............................................................................................... 70 Forming Compartments ............................................................................... 70 Compartment Types ..................................................................................... 77 Sounding Pipes ............................................................................................ 78 Damage Case Definition .............................................................................. 80 Cargo dropout .............................................................................................. 84 Damage Analysis and Partial Flooding........................................................ 85 Partial Flooding – Modelling and Analysis ................................................. 87 Key Points (e.g. Down Flooding Points) ..................................................... 93 Margin Line Points ...................................................................................... 95 Modulus Points and Allowable Shears and Moments ................................. 95 Floodable Length Bulkheads ....................................................................... 95 Stability Criteria........................................................................................... 96 v

Contents

Analysis Types ....................................................................................................... 96 Upright Hydrostatics .................................................................................... 97 Large Angle Stability ................................................................................. 100 Water on Deck – Stockholm Agreementt .................................................. 106 Equilibrium Analysis ................................................................................. 115 Specified Conditions .................................................................................. 118 KN Values Analysis................................................................................... 120 Limiting KG............................................................................................... 123 Limiting KG for damage conditions with initially loaded tanks................ 126 Floodable Length ....................................................................................... 130 Longitudinal Strength ................................................................................ 133 Tank Calibrations ....................................................................................... 136 MARPOL Oil Outflow .............................................................................. 141 Probabilistic Damage ................................................................................. 146 Starting and Stopping Analyses ................................................................. 179 Probabilistic damage Log file .................................................................... 179 Batch Analysis ........................................................................................... 183 Analysis Settings .................................................................................................. 185 Heel ............................................................................................................ 186 Trim ........................................................................................................... 187 Draft ........................................................................................................... 189 Displacement ............................................................................................. 189 Specified Conditions .................................................................................. 190 Permeability ............................................................................................... 190 Tolerances .................................................................................................. 190 Analysis Environment Options ............................................................................ 192 Fluids Analysis Methods ........................................................................... 193 Density of Fluids........................................................................................ 195 Hog and Sag ............................................................................................... 197 Waveform .................................................................................................. 197 Grounding .................................................................................................. 199 Stability Criteria......................................................................................... 200 Damage ...................................................................................................... 200 Analysis Output.................................................................................................... 200 Reporting ................................................................................................... 201 Copying & Printing.................................................................................... 203 Select View from Analysis Data ................................................................ 204 Saving the Maxsurf Stability Design ......................................................... 205 Exporting ................................................................................................... 206 Chapter 4 Stability Criteria ............................................................................................. 209 Criteria Concepts.................................................................................................. 209 Criteria List Overview ............................................................................... 210 Types of criteria ......................................................................................... 212 Criteria Procedures ............................................................................................... 213 Starting the Criteria dialog ......................................................................... 213 Resizing the Criteria dialog ....................................................................... 214 Working with Criteria ................................................................................ 214 Editing Criteria .......................................................................................... 216 Working with Criteria Libraries................................................................. 218 Criteria Results ..................................................................................................... 220 Criteria Results Table ................................................................................ 220 Report and Batch Processing ..................................................................... 222 Nomenclature ....................................................................................................... 222

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Contents

Definitions of GZ curve features ............................................................... 222 Glossary ..................................................................................................... 225 Chapter 5 Maxsurf Stability Reference .......................................................................... 227 Windows .............................................................................................................. 227 Assembly View and Property Sheet .......................................................... 227 View Window ............................................................................................ 227 Loadcase Window...................................................................................... 229 Damage Window ....................................................................................... 229 Input Window ............................................................................................ 230 Results Window ......................................................................................... 231 Graph Window........................................................................................... 235 Report Window .......................................................................................... 239 Toolbars ............................................................................................................... 242 File Toolbar................................................................................................ 242 Edit Toolbar ............................................................................................... 242 View Toolbar ............................................................................................. 242 Analysis Toolbar ........................................................................................ 243 Window Toolbar ........................................................................................ 243 Design Grid Toolbar .................................................................................. 243 Visibility Toolbar ....................................................................................... 243 Edge VIsibility Toolbar ............................................................................. 244 Render Toolbar .......................................................................................... 244 Report Toolbar ........................................................................................... 244 View (extended) Toolbar ........................................................................... 244 Design Grid Toolbar .................................................................................. 244 Extra Buttons Toolbar ................................................................................ 244 Menus ................................................................................................................... 245 File Menu ................................................................................................... 245 Edit Menu .................................................................................................. 248 View Menu ................................................................................................ 250 Case Menu ................................................................................................. 252 Analysis Menu ........................................................................................... 253 Display Menu............................................................................................. 255 Data Menu.................................................................................................. 259 Window Menu ........................................................................................... 260 Help Menu ................................................................................................. 261 Appendix A: Calculation of Form Parameters ............................................................... 262 Definition and calculation of form parameters .................................................... 262 Measurement Reference Frames ................................................................ 262 Nomenclature ............................................................................................. 264 Coefficient parameters ............................................................................... 264 Length ........................................................................................................ 265 Beam .......................................................................................................... 266 Draft ........................................................................................................... 267 Midship and Max Area Sections ................................................................ 268 Block Coefficient ....................................................................................... 269 Section Area Coefficient ............................................................................ 269 Prismatic Coefficient ................................................................................. 269 Waterplane Area Coefficient ..................................................................... 270 LCG and LCB ............................................................................................ 270 Trim angle .................................................................................................. 271 Maximum deck inclination ........................................................................ 271 Immersion .................................................................................................. 271

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Contents

MTc or MTi ............................................................................................... 271 RM at 1 deg................................................................................................ 272 Potential for errors in hydrostatic calculations ..................................................... 272 Integration of wetted surface area .............................................................. 272 Appendix B: Criteria file format .................................................................................... 274 Appendix C: Criteria Help.............................................................................................. 276 Parent Calculations............................................................................................... 276 Selecting a calculation in a criterion .......................................................... 276 Angle calculators ....................................................................................... 276 GM calculators........................................................................................... 277 Parent Heeling Arms ............................................................................................ 280 Heeling Arm Definition ............................................................................. 280 Parent Heeling Moments ........................................................................... 290 Parent Stability Criteria ........................................................................................ 292 Criteria at Equilibrium ............................................................................... 292 GZ Curve Criteria (non-heeling arm) ........................................................ 293 Heeling arm criteria (xRef) ........................................................................ 310 Heeling arm criteria ................................................................................... 311 Multiple heeling arm criteria ..................................................................... 323 Heeling arm, combined criteria.................................................................. 331 Derived heeling arm criteria ...................................................................... 335 Other combined criteria ............................................................................. 340 Specific stand alone heeling arm criteria ................................................... 341 Stand alone heeling arm criteria ................................................................ 341 Stand alone heeling arm combined criteria ................................................ 342 Appendix D: Specific Criteria ........................................................................................ 345 Dynamic stability criteria ..................................................................................... 345 Capsizing moment ..................................................................................... 345 Heeling arms for specific criteria - Note on unit conversion ............................... 347 IMO Code on Intact Stability A.749(18) amended to MSC.75(69)........... 347 IMO HSC Code MSC.36(63) .................................................................... 349 USL code (Australia) ................................................................................. 351 ISO 12217-1:2002(E) ................................................................................ 352 ISO 12217: Small craft – stability and buoyancy assessment and categorisation. ............................................................................................ 354 Appendix E: Reference Tables ....................................................................................... 356 File Extension Reference Table ........................................................................... 356 Analysis settings reference table .......................................................................... 357 Appendix F: Quality Assurance ..................................................................................... 358 Quality Assurance ................................................................................................ 358 Quality Principles ...................................................................................... 358 Structured Programming ............................................................................ 358 Verification of Algorithms ......................................................................... 358 Testing of Implementation ......................................................................... 361 Testing of Upgrades ................................................................................... 361 Beta Testing ............................................................................................... 361 Version Control.......................................................................................... 361 But we're not Perfect .................................................................................. 361 Index ............................................................................................................................... 362

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About this Manual

About this Manual This manual describes how to use Maxsurf Stability to perform hydrostatic and stability analyses on your Maxsurf design. Chapter 1 Introduction Contains a description of Maxsurf Stability functionality and its interface to Maxsurf Chapter 2 Quickstart Gives a quick walk through the analysis tools available in Maxsurf Stability. Chapter 3 Using Maxsurf Stability Explains how to use Maxsurf Stability' powerful floatation and hydrostatic analysis routines to best advantage. Chapter 4 Stability Criteria Gives details of the stability criteria that may be evaluated with Maxsurf Stability. Chapter 5 Maxsurf Stability Reference Gives details of Maxsurf Stability' windows and each of Maxsurf Stability' menu commands. If you are unfamiliar with Microsoft Windows® interface, please read the owner's manual supplied with your computer. This will introduce you to commonly used terms and the basic techniques for using any computer program.

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Chapter 1 Introduction

Chapter 1 Introduction Maxsurf Stability is a hydrostatics, stability and longitudinal strength program specifically designed to work with Maxsurf. Maxsurf Stability adds extra information to the Maxsurf surface model. This includes: compartments and key points such as downflooding points and margin line. Maxsurf Stability’ analysis tools enable a wide range of hydrostatic and stability characteristics to be determined for your Maxsurf design. A number of environmental setting options and modifiers add further analysis capabilities to Maxsurf Stability. Maxsurf Stability is designed in a logical manner, which makes it easy to use. The following steps are followed when performing an analysis:  Input model  Analysis type selection  Analysis settings  Environment options  Criteria specification and selection  Run analysis  Output

Maxsurf Stability operates in the same graphical environment as Maxsurf; the model can be displayed using hull contour lines, rendering or transparent rendering. This allows visual checking of compartments and shows the orientation of the vessel during analysis.

Input Model Maxsurf design files may be opened directly into Maxsurf Stability, eliminating the need for time-consuming digitising of drawings or hand typing of offsets. This direct transfer preserves the three-dimensional accuracy of the Maxsurf model. Tanks can be defined and calibrated for capacity, centre of gravity and free surface moment. Tanks and compartments can be flooded for the purpose of calculating the effects of damage. A number of loadcases can be created. The loadcase allows static weights and tankfillings to be specified and calculates the corresponding weights and centres of gravity as well as the total weight and centre of gravity of the vessel under the specified loading condition. Loadgroups may also be created and cross referenced into loadcases. Other input consists of: tank sounding pipes; key points, such as downflooding points, immersion and embarkation points; margin lines and section modulus.

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Chapter 1 Introduction

Analysis Types Maxsurf Stability contains the following analysis tools:  Upright hydrostatics  Large angle stability  Equilibrium analysis  Specified Condition analysis  KN values and cross curves of stability  Limiting KG analysis  Floodable Length analysis  Longitudinal Strength analysis  Tank Calibrations  MARPOL oil outflow  Probabilistic damage (Maxsurf Stability Ultimate only)

Although common analysis settings are used where possible, different analyses may require different settings. For example: the upright hydrostatics analysis simply requires a range of drafts; whereas the longitudinal strength analysis requires a detailed load distribution. The analysis settings for each analysis type are explained in detail in the analysis synopsis below.

Analysis Settings The analysis settings describe the condition of the vessel to be tested. For example, a range of drafts in the case of upright hydrostatics, or a range of heel angles for a large angle stability analysis. The following analysis settings are available:  Heel  Trim  Draft  Displacement  Permeability  Specified condition

The analysis settings are specified prior to running the analysis. Settings that are not relevant to the selected analysis type are greyed out in the Analysis menu.

Environment Options Environmental options are modifiers that may be applied to the model or its environment that will affect the results of the all the hydrostatic analysis types.

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Chapter 1 Introduction

Depending on the analysis being performed, different environmental options may be applied to the Maxsurf Stability:  Type of Fluid Simulation  Density (of fluids)  Wave form  Grounding  Intact and Damage condition

Stability Criteria Maxsurf Stability has the capability to calculate compliance with a wide range of stability criteria. These criteria are either derived from the properties of the stability curve calculated from a Large Angle Stability analysis or from the vessel’s orientation and stability properties calculated from an Equilibrium analysis. Limiting KG and Floodable length analyses also use stability criteria. Maxsurf Stability has an extensive range of stability criteria to determine compliance with a wide range of international stability regulations. In addition, Maxsurf Stability has a generic set of parent criteria from which virtually any stability criterion can be customized.

Output Views of the hull are shown for each stage of the analysis, complete with immersed sectional areas and actual waterlines. The centres of flotation, gravity and buoyancy are also displayed. Heeled and trimmed hullforms and water plane shapes may be printed. Results are stored and may be reviewed at any time, either in tabular form, or as graphs of the various parameters across the full range of calculation. All results are accumulated in the Report window (which can be saved, copied and printed), or output directly to a Word document. The criteria checks are summarised in tables listing the status (pass/fail) of each criterion as well as the margin. The criterion settings and intermediate calculation data may also be displayed if required. For a brief overview of the different analysis that Maxsurf Stability has available, continue reading Chapter 2 Quickstart.

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Chapter 3 Using Stability

Chapter 2 Quickstart This chapter will briefly describe each analysis type and its output. For each analysis type, a list of the required settings as well as the available environment options is given. Maxsurf Stability contains the following analysis types  Upright Hydrostatics  Large Angle Stability  Equilibrium Condition  Specified Condition  KN Values  Limiting KG  Floodable Length  Longitudinal Strength  Tank Calibrations  MARPOL Oil Outflow  Probabilistic Damage

Each analysis has different settings that may be applied  Heel  Trim  Draft  Displacement  Specified condition  Permeability  Loadcase  Tank and compartment definition

Maxsurf Stability offers different environment options that may be applied to the analyses  Fluid Densities  Treatment of fluids in tanks: fluid simulation or corrected VCG  Wave form  Grounding  Damage

Maxsurf Stability offers an extensive range of stability criteria that are applicable to equilibrium, large angle stability, limiting KG and Floodable length analysis. The Analysis types section describes each of the analysis types, settings and environment options in more detail.

Upright Hydrostatics Quickstart For Upright Hydrostatics, heel is fixed at zero heel, trim is fixed at a user defined value and draft is varied in fixed steps. Displacement and centre of buoyancy and other hydrostatic data are calculated during the analysis. Page 7

Chapter 3 Using Stability

Upright hydrostatics requirements  Range of drafts to be analysed  VCG (for calculation of some stability characteristics such as GMt and GMl only)  Trim

Upright hydrostatic options  Fluid Densities  Wave form  Damage  Compartment definition (in case of damage)

The results are tabulated and graphs of the hydrostatic data, curves of form and sectional area at each draft are available. Bonjean Curves are also calculated. For more detailed information please see: Upright Hydrostatics on page 97.

Large Angle Stability Quickstart For the analysis of Large Angle Stability, displacement and centre of gravity are specified in the loadcase. A range of heel angles are specified and Maxsurf Stability calculates the righting lever and other hydrostatic data at each of these heel angles by balancing the loadcase displacement against the hull buoyancy and, if the model is freeto-trim, the centre of gravity against the centre of buoyancy such that the trimming moment is zero. Large angle stability requirements  Range of heel angles to be analysed  Trim (fixed or free)  Loadcase or loadgroup  Tank definition in the case of tank loads being included in the Loadcase (and/or for the definition of damage)

Large angle stability options  Fluid Densities  Treatment of fluids in tanks: fluid simulation or corrected VCG  Wave form  Damage  Compartment definition (in case of damage)  Key points  Margin line and deck edge  Analysis of stability criteria  Water on Deck (WoD) – Stockholm Agreement

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Chapter 3 Using Stability

The key output value is GZ (or righting lever), the horizontal distance between the centres of gravity and buoyancy. A graph of these values at the various heel angles forms a GZ curve. Various other information is often overlaid on the GZ curve, including upright GM, curves for wind heeling and passenger crowding levers and the angle of the first downflooding point. These additional data depend on which (if any) stability criteria have been selected. A number of other graphs may be selected from the pull-down list in the graph window. Remember that you can access this data in tabular form by double clicking in the graph window:  Dynamic stability curve (Area under GZ curve, integrated from upright)  Variations of other hydrostatic and form parameters may be plotted against heel angle.

 Maximum safe steady heel angle  The sectional area curve at each of the heel angles tested may also be displayed.

Note that some of these graphs have parameters that may be adjusted in the Data Format dialog If large angle stability criteria have been selected for analysis, these results will also be reported in the criteria results table and they may lead to additional curves being displayed on the GZ curve. Downflooding angles for any key points, margin line and deck edge will also be computed and tabulated. For more detailed information please see: Large Angle Stability on page 100.

Equilibrium Condition Quickstart Equilibrium Analysis uses the Loadcase, to calculate the displacement and the location of the centre of gravity. Maxsurf Stability iterates to find the draft, heel and trim that satisfy equilibrium and reports the equilibrium hydrostatics and a cross sectional areas curve. Equilibrium analysis requirements  Loadcase or loadgroup  Tank definition in the case of tank loads being included in the Loadcase (and/or for the definition of damage)

 Compartment definition and damage case (in case of damage)

Equilibrium analysis options

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Chapter 3 Using Stability  Fluid Densities  Treatment of fluids in tanks: fluid simulation or corrected VCG  Wave form  Grounding  Damage  Compartment definition (in case of damage)  Key points  Margin line and deck edge  Analysis of equilibrium criteria

Equilibrium analysis result table lists the hydrostatic properties of the model. If a wave form has been specified there will be a number of columns; each column contains the results for a different position of the vessel in the wave as given by the wave phase value. The sectional area curve is also calculated, as is the freeboard to any defined key points, margin line and deck edge. Any equilibrium criteria will also be evaluated and their results reported. For more detailed information please see: Equilibrium Analysis on page 115.

Specified Condition Quickstart In the specified condition each of the three degrees of freedom, for which the hydrostatic properties of the model are to be calculated, can be set. Specified Condition Requirements  Specified Conditions Input Dialog

If fixed trim is specified, you may enter the trim or specify the forward and aft drafts (these are at the perpendiculars as specified in the Frame of Reference dialog). Specified Conditions options  Fluid Densities  Wave form  Damage  Tank and Compartment definition (in case of damage)

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Chapter 3 Using Stability

The output for the specified condition consists of a curve of cross sectional areas and hydrostatics of the vessel in the specified condition. For more detailed information please see Specified Conditions on page 118.

KN Values Quickstart KN values or Cross Curves of Stability are useful for assessing the stability of a vessel if its VCG is unknown. They may be calculated for a number of displacements before the height of the centre of gravity is known. The KN data may then be used to obtain the GZ curve for any centre of gravity height (KG) using the following formula: GZ = KN - KG * sin(Heel) where GZ is the righting lever measured transversely between the Centre of Buoyancy and the Centre of Gravity, and KG is the distance from the baseline to the vessel's effective Vertical Centre of Gravity. KN Values Analysis Requirements  Range of displacements to be analysed  Range of heel angles to be analysed  Trim (fixed or free)  Estimate of VCG (provides more accurate result if free-to-trim)  TCG (if required)

KN Values Analysis Options  Fluid Densities  Wave form  Damage  Tank and Compartment definition (in case of damage)

Output is in the form of a table of KN values and a graph of Cross Curves of Stability. If the analysis is performed free-to-trim and an estimate of the VCG is known, this may be specified. The computed KN results will then give a more accurate estimate of GZ for KG close to the estimated VCG since the effects of VCG on trim have been more accurately accounted for. For more detailed information please see KN Values Analysis on page 120.

Limiting KG Quickstart The Limiting KG analysis may be used to obtain the highest vertical position of the centre of gravity (maximum KG) for which the selected stability criteria are just passed. This may be done for a range of vessel displacements. At each of the specified displacements, Maxsurf Stability runs several Large Angle Stability analyses at different KGs. The selected stability criteria are evaluated; the centre of gravity is increased until one of the criteria fails. Limiting KG Analysis Requirements

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Chapter 3 Using Stability  Range of displacements to be analysed  Range of heel angles to be analysed  Trim (fixed or free)  Stability criteria for which limiting KG is to be found  TCG (if required)

Limiting KG Analysis Options  Fluid Densities  Wave form  Damage  Tank and Compartment definition (in case of damage)  Laodcase (in case of initial loading of damaged tanks)  Key points (if required for criteria)  Margin line and deck edge (if required for criteria)

A graph of maximum permissible GZ plotted against vessel displacement is produced as well as tabulated results indicating which stability criteria limited the VCG. If limiting curves are required for each of the stability criteria individually, this may be done in the Batch Analysis mode. A check will be made to ensure that any selected equilibrium criteria are passed, however at least one large angle stability criterion is required. Only relevant criteria will be used, i.e. if a damage case is chosen, only damage criteria will be evaluated; if the intact condition is used, only intact criteria will be evaluated. Some criteria, such as angle of maximum GZ, are very insensitive to VCG and may prevent the analysis converging. If the analysis is unable to converge for a certain displacement this will be noted and the next displacement tried. For more detailed information see Limiting KG on page 123.

Floodable Length Quickstart This analysis mode is used to compute the maximum compartment lengths based on user-specified equilibrium criteria. Floodable Lengths may be computed for a range of displacements; the LCG may be specified directly or calculated from a specified initial trim. In addition a range of permeabilities may be specified. The VCG is also required to ensure accurate balance of the CG against the CB at high angles of trim. As well as the standard deck edge and margin line immersion criteria (one of which must be specified) the user can also add criteria for maximum trim angle and minimum required values of longitudinal and transverse metacentric height. Floodable Length Analysis Requirements

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Chapter 3 Using Stability  Range of displacements to be analysed  VCG  Range of permeabilities to be analysed  Trim (free- to- trim to either initial trim or specified LCG)  Floodable length criteria to be tested

 Margin line and deck edge (required for criteria)

Floodable Length Analysis Options  Fluid Densities  Wave form

The output is in the form of tabulated Floodable Lengths for each displacement and permeability. The data is tabulated for each of the stations as defined in Maxsurf. The data is also presented graphically. For more detailed information please see Floodable Length on page 130.

Longitudinal Strength Quickstart Maxsurf Stability calculates the net load from the buoyancy and weight distribution of the model. That data is then used to calculate the bending moment and shear force on the vessel. Longitudinal Strength Analysis Requirements  Loadcase (including distributed loads if required)  Tank definition in the case of tank loads being included in the Loadcase (and/or for the definition of damage)

Longitudinal Strength Analysis Options  Fluid Densities  Treatment of fluids in tanks: fluid simulation is always used for Longitudinal Strength analysis

 Wave form  Grounding  Damage  Compartment definition and damage case (in case of damage)  Allowable shear and bending moment

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Chapter 3 Using Stability

The longitudinal strength graph and tables contain all information on weight and buoyancy distribution, the shear force and bending moment on the vessel. If defined, graphs of allowable shear and bending moment are superimposed on the graph. For more detailed information please see Longitudinal Strength on page 133.

Tank Calibrations Quickstart Tanks can be defined and calibrated for capacity, centre of gravity and free surface moment (FSM). Fluid densities and tank permeabilities can be varied arbitrarily. Tank calibrations may be calculated for a range of trim and heel angles. Maxsurf Stability uses its fluid simulation mode to calculate the actual position of the fluids in the tanks, taking into account the vessel trim and heel; i.e. the position of the fluid in the tank will be computed so that the fluid surface is parallel with the external seawater surface. Tank ullages are measured from the top of the sounding pipe to the free surface of the liquid within the tank along the sounding pipe and in a similar manner, soundings are measured from the bottom of the sounding pipe to the free surface. Tank calibrations may be performed for a range of heel and trims. The results for a single condition are shown in the results table. The condition to be viewed may be selected from the Results toolbar; Tabulated results may be customised using the Data Format dialog:

Tank calibration analysis requirements  Tank definitions  Sounding pipe definition (if required)  Sounding intervals for calibration levels  Trim range  Heel range

Tank calibration analysis options

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Chapter 3 Using Stability  Fluid Densities  Treatment of fluids in tanks: fluid simulation always selected  Damage: Intact case always selected  What to calibrate (Analysis | Calibration options)

For each tank, a table of capacities, volumes etc. is calculated. These results are presented in both tabular and graphical forms. For more detailed information please see Tank Calibrations on page 136.

MARPOL Oil Outflow Quickstart MARPOL probabilistic oil outflow calculation may be computed according to the following MARPOL regulations: Resolution MEPC.141(54), Regulation 12A: Oil fuel tank protection Resolution MEPC.117(52), Regulation 23: Accidental oil outflow performance Seltect the Reolution and tanks to be included in the analysis in the MARPOL options (Analysis menu) dialog. Then in the MARPOL results data table, edit any values as required; the resulting oil outflows will be calculated automatically. The “Start Analysis” button will send the tabulated results to the Report. For more detailed information please see MARPOL Oil Outflow on page 141

Probabilistic Damage Quickstart Attained index using probabilistic damage analysis may be computed. Probabilistic damage analysis requirements  Loadcase definitions  Tank and compartmentation definition  Main probabilistic damage analysis parameters and criteria setup  Subdivision definitions  Heel angle range for GZ curve calculation  Trim

Probabilistic damage analysis options  Treatment of fluids in tanks: fluid simulation or corrected VCG  Wave form  Key points  Margin line and deck edge

For more detailed information please see the Probabilistic Damage section on page 146.

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Chapter 3 Using Stability

Chapter 3 Using Maxsurf Stability This chapter describes  Getting Started  Maxsurf Stability Model  Analysis Types  Analysis Settings  Analysis Environment Options  Analysis Output

Getting Started This section contains everything you need to do to start using Maxsurf Stability  Installing Maxsurf Stability  Starting Maxsurf Stability Installing Maxsurf Stability

Install Maxsurf Stability by inserting the CD and running the Setup program, then follow the instructions on screen. Note: Before installing any program from the Maxsurf suite for the first time, please read the purchase letter (also referred to as installation manual). Starting Maxsurf Stability

After installation, Maxsurf Stability should be accessible through the Start Menu. Simply select Maxsurf Stability from the Maxsurf menu item under Programs in the Start menu. Windows Registry

Certain preferences used by Maxsurf Stability are stored in the Windows registry. It is possible for this data to become corrupted, or you may simply want to revert back to the default configuration. To clear the Maxsurf Stability preferences, start the program with the Shift key depressed. You will be asked if you wish to clear the preferences, click OK, doing this will reset all the preferences. The following preferences are stored in the registry:

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Chapter 3 Using Stability  Colour and line thickness settings of contours and background  Fonts  Window size and location  Size of resizing dialogs (alternatively, these may be reset by holding down the shift key when activating them)

 Density of fluids  Heel angles for large angle stability, KN and Limiting KG analyses  Permeabilities for floodable length analysis  Location of files  Units for data input and results output  Convergence tolerance (Error values)  Maximum number of loadcases  Reporting preferences

Note: The default density for the fluid labelled "Sea Water" is stored in the windows registry. All hydrostatic calculations use this. Check the density of seawater after resetting your preferences. It is recommended to save your customized densities with your project using the File | Save Densities As command.

Maxsurf Stability Model This section describes how to open a Maxsurf model in Maxsurf Stability and provides some important information to ensure that your model is correctly interpreted by Maxsurf Stability.  Preparing a Design in Maxsurf  Opening a New Design  Opening an Existing Maxsurf Stability Design File  Updating the Maxsurf Stability Model  Maxsurf Stability Sections Forming  Checking the Maxsurf Stability model

After checking the Maxsurf Stability model, the next step is to check the Maxsurf Stability settings and initial analysis conditions.  Setting Initial Conditions

Depending on the analysis performed, you may need to set up the following additional model data:

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Chapter 3 Using Stability  Working with Loadcases  Modelling Compartments  Forming Compartments  Compartment Types  Damage Case Definition  Sounding Pipes  Key Points (e.g. Down Flooding Points)  Margin Line Points  Modulus Points and Allowable Shears and Moments  Stability Criteria Preparing a Design in Maxsurf

There are several important checks that must be carried out in Maxsurf before opening a design in Maxsurf Stability:  Setting the Zero Point  Setting the Frame of Reference  Setting the Windage Surfaces  Skin Thickness  Outside Arrows  Trimming  Coherence of the Maxsurf surface model Setting the Zero Point

Ensure that the zero point is correctly setup in Maxsurf. A consistent zero point and frame of reference should be used for the model throughout the Maxsurf suite. In Maxsurf Stability you have the option of displaying longitudinal measurements such as LCB or LCF from the model zero point or amidships. Setting the Frame of Reference

It is vital that the Frame of Reference is correctly setup in Maxsurf before attempting to analyse the model in Maxsurf Stability. The Frame of reference should not be changed in Maxsurf Stability. The frame of reference defines the fore and aft perpendiculars, the baseline and the datum waterline; midships is automatically defined midway between the perpendiculars. By convention, in the profile and plan views, the vessel’s bow is on the right. The perpendiculars define the longitudinal positions of the vessel’s draft marks and cannot be coincident. The base line is the datum from which the drafts and KG are measured. The frame of reference cannot be changed in Maxsurf Stability. However it is possible to specify upto nine additional locations at which the drafts should be reported. This is done through the Data | Draft Marks dialog. Note: Draft and Trim specification It should be remembered that the drafts specified for an analysis are the drafts at the perpendiculars (or amidships) and the trim specified (and reported) is the difference between the draft at the AP and draft at the FP. Page 18

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Setting the Windage Surfaces

Windage areas and underwater projected areas definitions have been added to the Maxsurf vessel model. These data may be defined and edited in both Maxsurf Modeler and Maxsurf Stability via the Windage Surfaces dialog in the Data menu.

Windage Surfaces dialog (Data menu)

If no Windage groups are defined, then the older system for the calculation of windage and lateral projected underwater area is used. That is the hydrostatic sections are projected into the transverse plane. The outer perimeter formed by joining the upper and lower limits of these projected sections is then used to calculate both the windage area of the hull and the underwater projected area. The zero-trim waterline at the current midship draft is used to determine which part of the projection is underwater and which part is windage area. Because of these limitations, the effects of vessel trim and "holes" in the model are not accounted for by this older method. The new method overcomes these limitations as well as adding new features. Windage Groups

The concept of a Windage Group has been added. This groups together model surfaces which should be treated as a single object. There are always at least two Windage Groups and the first one defines the surfaces that should be used to calculate the underwater lateral projected area. Individual surfaces may be included in multiple Windage Groups. Apart from the underwater group, Windage Groups have various factors associated with them:  F_drag: winage drag factor; default value 1.0  F_shield: shielding factor; default value 0.0  F_user: a user-defined factor; default value 1.0  Ftotal  Fdrag .1.0  Fshield .Fuser Windage Groups may be added and deleted with the respective buttons in the dialog. The surfaces to be included in each group are defined in selected by double clicking in the "Surfaces" cell in the table, in a similar manner to the selection of boundary surfaces for Tanks and Compartments. Page 19

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Windage Group definition and Surface selection

The color of the Windage Profile outline can be changed in the Colors dialog; the underwater profile is shown using the "Immersed Sections" color.

Color selection

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Wind direction

The Windage direction specifies the projection direction used for the surfaces: 90deg. gives a projection in the lateral plane; 0deg. gives a direction in the longitudinal plane. Angles between 0 and 180deg are allowed since the sign of the projection vector does not matter. Note that to improve performance, the projected windage contour uses a fairly coarse surface mesh. This may result in the projected windage contour not exactly corresponding with the surface edges, but the effect on projected area and center of area is negligible. Due to the calculation method used for the projected conoturs, it is possible that some visual artifacts may be present but again these have negligible effect on projected area and center of area.

Windage projections viewed in profile at 90deg (upper) and 70deg (lower) Display

In Maxsurf Stability, when the vessel is at the DWL, the normal windage profile view is shown and the wind profile groups may be modified. However once a Large Angle Stability analysis has been performed, it is possible to select the windage profile used for any of the defined velocity profile wind heeling arms (see below for deails).

Display | Windage Profile dialog Effect of heel

Maxsurf Stability has the option of using just the upright (zero heel) projected windage profile or calculating the actual projection of the heeled vessel. The option is specified in Edit | Preferences dialog. It should be noted that calculating the projected windage profile at each heel angle can add significantly to the time required to complete the analysis. For criteria evaluation, the underwater lateral projected area and center of area for the upright (zero heel) vessel is always used; however the wind heeling moment will use the actual inclined (including heel) projected windage area if this option has been selected in the Preferences dialog.

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Upright or heeled/inclined projected windage area calculation preference

Windage profile calclated for the upright vessel and used for all heel angles

Windage profile calclated using heeled/inclined projected windage area method

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Surface Use

In Maxsurf you can choose between two types of surface use Hull Hull surfaces are used to define the watertight envelope of the hull. Internal structure Internal structure surfaces are used for all other surfaces (any surfaces which do not make up the watertight envelope) and also surfaces which are to be used in Maxsurf Stability to define the boundaries of tanks and compartments that have complex shapes. The following table describes the difference between each surface use in Maxsurf Stability: Included:

Hull Shell

Internal Structure

Hydrostatic sections Selection of tank/compartment boundaries Skin thickness applied to the surface Verify that all surfaces that are to be used as tank/compartment boundaries are defined as Internal Structure. If a surface is defined as internal structure, it is not included as part of the hull shell by Maxsurf Stability, i.e. internal surfaces will be ignored in the forming of hydrostatic sections. Skin Thickness

If skin thickness is to be used in hydrostatic calculations, ensure that the thickness and projection direction have been specified for the hull shell surfaces. Thickness can be specified differently for each hull surface, resulting in more accurate hydrostatics. To activate skin thickness in Maxsurf Stability ensure that the “Include Skin Thickness” option is selected when reading the file or calculating the hull sections. Note Tank boundaries made from internal structures surfaces do not have skin thickness. To include skin thickness, the internal structure surface should be placed to model the inside of the tank if the tank wall has significant thickness. Skin thickness for hull surfaces will be treated so that the hull sections go to the outside of the plate whilst any tanks are trimmed to the inside of the plate. Outside Arrows

The surfaces’ outside arrows define the orientation of the surfaces. Ensure that you have used the Outside Arrows command from the Maxsurf Display menu to define which direction points outwards (towards the seawater) for each surface. The surface direction may be flipped by clicking on the end of the arrow.

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Trimming

Ensure that all surfaces are trimmed correctly. At any longitudinal position on the hull, you should have completely closed transverse sections or sections with at most one opening (e.g. the deck).

Correct Section with no opening.

Correct section with one opening: this section will be closed across the top.

Also see: Maxsurf Stability Sections Forming on page 31 Checking the Maxsurf Stability model on page 34 Coherence of the Maxsurf surface model

Maxsurf Stability will generally have no problem correctly interpreting your design as long as the following requirements for the Maxsurf model are observed:  Make sure that each surface touches its adjacent surfaces at its edge, preferably by bonding the edges together

 Where surfaces intersect, trim away the excess regions of the surface; e.g. the part of the keel that is inside the hull and the part of the hull that is inside the keel

 Do not have surfaces that cannot be closed in an unambiguous fashion, i.e. a maximum of one gap in a transverse section through the hull.

 Remember that the inner portions of each intersecting contour will be trimmed off  Check surface use; internal structure surfaces are ignored when forming the hull sections in Maxsurf Stability

Note: For groups internal structure surfaces that will be used to define tank (or compartment boundaries) the same requirements apply. Also see: Checking the Maxsurf Stability model on page 34.

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Opening a New Design

File opening in Maxsurf Stability is window specific, i.e. Maxsurf Stability will automatically look for compartment definition files when you are in a Compartment Definition window and a loadcase in a Loadcase window. To open a design for analysis, ensure that the design view window is active, then select Open Design from the File menu. Choose a Maxsurf design file (.msd). The following dialog will appear:

Calculate new Sections

Choosing Calculate Sections will calculate the specified number of sections through the hull. These will then be used for the Hydrostatics calculations. The meaning of (ignore existing data, if any) is explained in Opening an Existing Maxsurf Stability Design File. Include Plating Thickness

At this stage, any surface thickness specified in the Maxsurf Surface Properties dialog may be included. Use Trimmed Surfaces

If the Maxsurf model has trimmed surfaces, the Use Trimmed Surfaces item should be ticked. Stations

When calculating stations, you may select how many stations should be used. Reducing the number of stations will speed up the analysis time but reduce the accuracy, conversely increasing the number of stations will increase the analysis time but lead to higher accuracy results; the maximum number of stations which may be used is 500. The first option allows you to use the station grid created in Maxsurf. This is extremely useful for hulls that have features such as keels or bow thrusters that need to be accurately modelled and may need a locally denser station spacing to do so. It also allows designs with significant longitudinal discontinuities in their sectional areas to have stations specified either side of the discontinuity, avoiding any errors inherent in the integration of evenly spaced stations. For example, if it was known that a design had a significant discontinuity in its sectional area curve at amidships, by specifying one station 1mm aft of amidships and one station 1mm forward of amidships this discontinuity can be modelled very accurately.

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Surface Precision

The Surface Precision options has two functions:  Setting for calculating the hydrostatic sections  Setting used to form new compartments or tanks.

The precision at which the design was saved in Maxsurf is included in the Maxsurf design file (.msd). Maxsurf Stability recognises this precision setting and will and set the Surface Precision button accordingly. Note: Maxsurf surface trimming information may vary for different precisions. Therefore it is recommended not to change the precision setting when opening the Maxsurf design file in Maxsurf Stability. The accuracy of the results depends much more on the number of sections than the accuracy at which the sections are calculated. Reducing the precision of the sections can greatly improve performance, usually at relatively small impact on the accuracy of the hydrostatics. Opening an Existing Maxsurf Stability Design File

After saving the Maxsurf design file for the first time in Maxsurf Stability, a “Maxsurf Stability Design file” (.hmd) is created. The Maxsurf Stability design file will consist of the hydrostatic sections and all input data such as loadcases, compartment definition, key points, sounding pipes etc. Maxsurf Stability also allows saving of all input and output files into individual files. To open an existing design, there are two options:  Double click on the .hmd file from any Windows explorer window  Use the Maxsurf Stability Open command form the file menu and select the .msd file

An existing Maxsurf Stability design consists of a number of files with different file extensions.

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When Maxsurf Stability opens a .msd file, it will look for a .hmd file with the same name as the .msd file. For example: when opening OSV.msd, the OSV.hmd file is found. The Calculate Sections dialog now has the option to read the sections from the file.



Ensure “Read existing data and sections” is selected and click OK.

Maxsurf Stability will now open the .hmd file. This contains hydrostatic sections information and all input information from last time the .hmd file was saved, i.e. compartment definitions, loadcases, damage cases, key points etc. Notes: 1) When selecting “Read existing data and sections (do not update geometry)” the Maxsurf surface information is not recalculated. This means that changes to the hull shape in the Maxsurf Design file, are not automatically incorporated. You will load your existing sections, loadcases and compartment definitions etc. See: Updating the Maxsurf Stability Model on page 30 for more information. 2) Calculate new sections (ignore existing data, if any) means that Maxsurf Stability will recalculate the hull sections and ignore any data stored in the .hmd file. You will have to reload your individual loadcases and compartment definition files etc after you have selected this option and pressed OK. Do not choose this option if you wish to keep the additional Maxsurf Stability data and you have not yet saved them as individual files as if the model is saved in Maxsurf Stability the .hmd file will be overwritten and any existing data lost. For more information on file properties and extensions in Maxsurf Stability, please see: File Extension Reference Table on page 356. Effect of Zero Point change

The description below relates to what happens in the following situation:

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Chapter 3 Using Stability  A hull model is generated in Maxsurf  Tank and load etc. data is then created in Maxsurf Stability and that data all saved in the .hmd file (as is done when you chose Save when the drawing window is top most).

 The model is closed in Maxsurf Stability  The model is opened in Maxsurf and for some reason the location of the zero point is changed

 The model is reopened in Maxsurf Stability and the tank and load etc. data is automatically read from the .hmd file. Maxsurf Stability 13 behaviour

It may sometimes occur that the model zero point location is changed in Maxsurf after tank, loadcase. Etc. data is defined in Maxsurf Stability. In previous versions of Maxsurf Stability this could cause problems because the loadcase and tank data maintained their position relative to the zero point, where as the key points and margin line remained in the same position relative to the hull. The two images from Maxsurf Stability 13 show this problem. The first image shows the model as initially defined in Maxsurf Stability with the zero point amidships and at the baseline. In the second image, the zero point has been moved (in Maxsurf) to the aftperpendicular and the DWL. Note that whilst the margin line and key points have remained in their same locations relative to the hull, the tanks and centre of gravity (from the loadcase) have remained in their same locations relative to the zero point.

Original location of data as entered in Maxsurf Stability before zero point change in Maxsurf.

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Effect of Zero point change in Maxsurf 13. Maxsurf Stability 14 behaviour

To rectify this problem, when loading a .hmd file, Maxsurf Stability now detects if the zero point has been modified in Maxsurf when the model is reopened in Maxsurf Stability. Note that this is only possible with Maxsurf Stability models that have been saved from the new version of Maxsurf Stability (because the new version of Maxsurf Stability now saves the zero point independently so that it can check for changes).

Original location of data as entered in Maxsurf Stability before zero point change in Maxsurf.

Now, if the zero point has changed, Maxsurf Stability will display the following message:

If the zero point is moved in Maxsurf, you will now be prompted.

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Selecting “yes” will maintain the position all the Maxsurf Stability data relative to the hull; essentially just the zero point it moved. This of course means that the numerical values of the various data are changed:

Click “yes” to maintain position of tanks, loads etc relative to the hull.

Selecting “no” will move all data other than the margin line with the zero point. Thus the tanks and loads etc. will move relative to the hull, but their numerical values will remain the same: The example shown is quite extreme, it is more likely that this option would be selected if it was realised that the zero point for the tank plan were slightly different than the zero point of the lines plan and a small correction to the zero point was required.

Click “no” to maintain position relative to zero point.

Updating the Maxsurf Stability Model

To update the hydrostatic sections to the latest Maxsurf Design File, select “Recalculate Hull sections” in the analysis menu after reloading the Maxsurf Design File with the “read existing data and sections from file” option selected. This function can also be used to include/exclude surface thickness or change the number of sections and to change use/not use trimmed surfaces without reloading the Maxsurf Design File. The “Recalculate Hull Sections” command recalculates Hull surfaces as well as Tank Boundary surfaces (Internal Structure surfaces in Maxsurf). Any tanks and loadcases will also be updated with this command.

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Note: Changes to the Maxsurf design are only recalculated after the new Maxsurf design has been re-loaded into Maxsurf Stability. This means that if the model is simultaneously being edited in Maxsurf and Maxsurf Stability, it is necessary to: 1) save and close the model in Maxsurf Stability 2) save in Maxsurf 3) open in Maxsurf Stability, using “Read existing data and sections” to make sure the loadcase, compartment definition etc remain part of the Maxsurf Stability design file. 4) use the “Recalculate Hull Sections” from the analysis menu. Maxsurf Stability Sections Forming

Maxsurf Stability works by applying trapezoidal integration to data calculated from a series of cross sections taken through the Maxsurf model surfaces. Maxsurf Stability will automatically form these sections, called “Maxsurf Stability sections”, “hydrostatic sections” or just “sections”. Maxsurf Stability deals only with sections that are completely closed, or can be unambiguously closed. This section outlines the section forming process used in Maxsurf Stability and may be helpful when preparing a Maxsurf design for Maxsurf Stability. Whilst it is always preferable to give Maxsurf Stability a completely closed model with no ambiguities, Maxsurf Stability will try to resolve any problems with the model definition in the manner outlined in the following sections. Note: The golden rule is that for any longitudinal position, the section must be made up of closed, non-intersecting (and non-self-intersecting) contours. In practice, one opening is acceptable and this will be automatically closed with a straight line. Furthermore, contours cannot be contained wholly within another contour. The same is true for groups of internal surfaces that have been selected to define a tank boundary.

Where a section consists of an open shell (e.g. a hull surface with no deck), Maxsurf Stability will automatically close the section with a straight line connecting the opening ends.

Section forming process in Stability

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Insufficient data for Stability to interpret the section

In the example above, if either the top or bottom gap had been closed in Maxsurf the design would cease to be ambiguous. Multiple surfaces that are trimmed correctly, bonded together or use compacted control points will not cause any problems when opened in Maxsurf Stability. Maxsurf Stability will form a closed section through multiple surfaces by linking the curve segments together.

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Stability closes the outside contour and trims remnants

A section through a multihull containing a single closed contour

A section comprising two closed contours

Maxsurf Stability will link curve segments together if they are only separated by a small amount. The user cannot change these tolerances, because there are too many dependencies in the program. Where surfaces intersect, Maxsurf Stability will make an attempt to remove excess portions of the curve to form a single continuous contour. However this is not always possible so it is much better practice to trim the model correctly manually.

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Ambiguous Sections (e.g. decks, bulwarks)

A common example of ambiguous sections is a model with multiple decks. Maxsurf Stability will have difficulties distinguishing the intended main deck.

Avoid using "Hull" surfaces for intermediate decks

The example above has bulwarks; generally these will be treated correctly by Maxsurf Stability and removed, but this depends on the height of the bulwark relative to the rest of the section. To prevent ambiguities it is recommended to trim the bulwark in Maxsurf. If the bulwark’s volume is expected to influence the hydrostatic calculations, the bulwark’s volume has to be properly modelled in Maxsurf by modelling both the outside and the inside of the bulwark. Checking the Maxsurf Stability model

Before starting any analysis you should check whether Maxsurf Stability has been able to correctly interpret your design. The following tools are available to validate the Maxsurf Stability model.  Show Single Hull Section  Checking the Sectional Area Curve  Using Rendering to Check the Model

Note: Sections that are not formed correctly cause the majority of problems with Maxsurf Stability models. Therefore, checking your sections after opening the design in Maxsurf Stability is strongly recommended. Incorrect sections in the model will give incorrect results. These sections should be continuous with no gaps and no unexpected lines. In particular, look closely at intersections between surfaces to make sure that Maxsurf Stability has interpreted the shape correctly.

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Show Single Hull Section

In the body plan view, you can step through the sections one-by-one to verify that they have been correctly calculated. This is done by selecting Show Single Hull Section in Body Plan view from the Display menu. You can then click in the inset box to view the sections, the left and right arrow cursor keys will enable you to step through the sections one-by-one. This works the same as the Maxsurf body plan window and is an extremely powerful tool to validate your Maxsurf Stability model. For more information see the Maxsurf manual.

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Checking the Sectional Area Curve

Another way of checking the Maxsurf Stability model is to perform a specified condition analysis at quite deep draft and look carefully at the sectional area curve in the graph window. If this displays any unexpected spikes or hollows Maxsurf Stability may not have correctly interpreted the hull shape. This is not a foolproof method since it does not necessarily highlight problems in the non-immersed part of the hull.

This Cross Sectional Area curve indicates there may be a problem with section forming from 12 m to 16 m. Using Rendering to Check the Model

The model may also be rendered, which makes it easier to see if there are any areas of the model which have not been properly defined. Select Render from the Display menu whilst in the perspective view and turn on the sections:

Note: In rare instances incorrect rendering may occur. This does not necessarily mean that the model is incorrect. As long as the sections are formed correctly, the model is correct.

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Further detailed checking of hull and tank/compartment sections

When checking that your model is correct, you are interested in whether the sections are correct. To do this go to the body plan view in Maxsurf Stability and select “Show Single Section”:

Then to check that the tanks are OK, leave the view as it is, but turn on the visibility of all the tanks of interest (if there are few tanks, then you can show all of them, if there are many it may help to hide some and check a few at a time). In the single section view, only tank sections near the current hull section are shown:

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Setting Initial Conditions

All Maxsurf Stability calculations are performed in the frame of reference of the model. Maxsurf Stability uses the aft perpendicular and forward perpendicular together with the baseline and the zero point for all calculations and gives the results in the units specified in the display menu. Note: Before you run any analysis using Maxsurf Stability, it is important that you set up the required initial conditions for the design. Coordinate System

Maxsurf Stability uses the Maxsurf coordinate system:

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Longitudinal Transverse Vertical

+ve forward +ve starboard +ve up

View window

View direction

-ve aft -ve port -ve down

Chapter 3 Using Stability

Body plan Plan Profile

From the stern, looking fwd From above, Port side above the centreline (this the opposite direction to Maxsurf) From Starboard, bow to the right.

Frame of Reference and Zero Point

It is essential that a frame of reference be specified. This should be done in Maxsurf and not in Maxsurf Stability. Draft and trim are measured on the forward and aft perpendiculars. If these are not in the correct positions, some analysis results will be meaningless or may even fail to complete. See: Setting the Zero Point and Setting the Frame of Reference on page 18. Note: Changing the zero point in Maxsurf will not update the compartment definition, loadcase and other input values. Changing the zero point after you have started analysing the model in Maxsurf Stability is not recommended. Draft Marks

Drafts are automatically calculated at the perpendiculars and amidships, should you require drafts to be calculated at other locations, you may specify upto nine additional locations at which the drafts should be reported. This is done through the Data | Draft Marks dialog. Drafts are always measured to the Baseline in the centre plane of the vessel. Immersed depth measurements are made perpendicualar to the free-surface.

Difference between “Immersed depth” and “Draft” measurements

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User-defined Draft Marks

Note that the Trim is still defined as the difference between the drafts at the perpendiculars and the Midship draft (used to define the range of immersions for the Upright Hydrostatics analysis) is the mean of the drafts at the perpendiculars; i.e. neither of these values has changed and neither are affected by the user-defined draft locations. Drafts can only be defined when the vessel is rotated to the DWL (Display | Set vessel to DWL).

User-defined draft locations and new toolbar button

The draft marks allow a user-defined datum to be specified. As with normal drafts measured to the Baseline, these drafts are also measured perpendicular to the Baseline (i.e. perpendicular to the DWL of the vessel at zero trim). (Noting that immersed depths to underside of keel –USK- are measured perpendicular to the actual (trimmed, heeled) waterplane.

Custom Draft Marks extended to provide user-defined datum

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Different types of user-defined draft measurements

Note: Draft and Trim specification It should be remembered that the drafts specified for an analysis are the drafts at the perpendiculars (or amidships) and the trim specified (and reported) is the difference between the draft at the AP and draft at the FP.

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Customising Coefficients

In Maxsurf Stability you may choose between the length between perpendiculars and the waterline length for the calculation of Block, Prismatic and Waterplane Area Coefficients. You may also select the draft, beam and sectional area to be used for calculation of these coefficients. The LCB and LCF can be displayed in the Results windows relative to the specified Zero Point, Amidships location, Aft Perpendicular, Fwd Perpendicular or from the Aft, Middle or fwd end of the actual waterline. You can also specify whether you want the forward (towards the bow) or the aft (towards the stern) to have a positive sign. Finally you can chose whether you want the LCB and LCF to be displayed as a length or as a percentage of the waterline or LPP length as specified in the Length for Coefficients.

Data | Coefficients dialog

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Setting Units

The units used may be specified using the Units command. In addition to the length and weight (mass) units, units for force and speed (used in wind heeling and heeling due to high-speed turn etc. criteria) and the angular units to be used for areas under GZ curves, may also be set. The angular units for measuring heel and trim angles are always degrees. Units may be changed at any time.

Other Initial Conditions

See: Fluids Analysis Methods on page 193 Density on page 195 Working with Loadcases

Loadcases define the loading condition of the vessel. Static weights that make up the vessel lightship are specified here as well as tank filling levels, expressed as either a percentage of the full tank capacity or as a weight. Loadcases automatically contain all the tanks defined in the Tank definition. Loadgroups are special loadcases that contain no tanks. These may be used to define groups of fixed weights (such as the steel weight or lightship weight) in a single location which may then be cross-referenced into a loadcase. Any changes to the loadgroup are then automatically incorporated into any loadcases that reference them. A loadgroup is included in a loadcase simply by specifying the loadgroup name in the “Item Name” column.

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The loadcase will normally update the column totals automatically as weights or tank loadings are changed. The exception to this is if tanks have not yet been formed or the vessel is still rotated from the result of an analysis. If the loadcase does not update, click on the update Loadcase button and ensure that the hull is at the DWL by selecting “Set vessel to DWL”:

The individual loads can be displayed graphically:

Creating a new Loadcase File

To create a load case, switch to the loadcase view by selecting Loadcase from the Loadcase sub-menu in the Window menu. Then select “New Load Case” from the File menu or press Ctrl+N. A new load spreadsheet will be displayed in the Loadcase window. The default loadcase will contain a lightship entry and an entry for each tank (with a default filling of 50%).

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The tabs in the bottom of the window can be used to skip through the different loadcases in the design. Create New Loadcases based on Template

To avoid rework, an existing loadcase may be used as a template when creating a new loadcase. To do this, 

In the loadcase window, select the Loadcase you wish to use as a template

Bring the loadcase you wish to use as a template to the front for example by clicking on the tab on the bottom 

select File | New

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First, you will be asked for a new Loadcase name after which the following dialog appears:

A new loadcase will appear in one of the blank (…) loadcase tabs. If there are no blank tabs left, you will either have to close an existing loadcase, or add more loadcases using the Case | Max. Number of Loadcases command. Note The template is only used during the creation of the loadcase. Once a loadcase has been created from a template loadcase, changes made in the template are NOT automatically changed in the loadcase derived from it. Naming and Saving a Loadcase

A loadcase can be given any name by saving it to a separate file where the loadcase filename will be used as the loadcase name and displayed on the tab in the loadcase window. Alternatively, 

Select Edit Loadcase from the Case menu



Changing the name in the Loadcase Properties dialog.

The next time you use the File | Save Loadcase command you will be asked to confirm the loadcase file name. Loading a Saved Loadcase

You can load a saved loadcase into your loadcase window by: 

Select an empty tab in the loadcase window that you wish to load the loadcase into

Empty tab.

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If there are no empty tabs, you should either increase the maximum number of loadcases (see below), or close an existing loadcase. 

Select File | Open Load Case



Select the .hml file you wish to open.

Setting the Maximum Number of Loadcases

The maximum number of loadcases (up to twenty-five) that can be loaded in Maxsurf Stability at any one time is set by selecting “Max. Number of Loadcases” from the Case menu. You may then enter the maximum number of load cases you require.

You must restart Maxsurf Stability for this change to take effect. In most cases, you will only need to set this once to the maximum number of loadcases you are ever likely to use. For convenience of use, a sensible number is recommended. Each loadcase can be selected and used for analysis. Each may be saved and loaded independently, effectively allowing you as many loadcases as you require. Note: When loading a design that has more loadcases than the maximum you have currently set in Maxsurf Stability, you will receive a warning and the file will not be loaded. You must increase the maximum number of allowable loadcases and restart Maxsurf Stability before you can load the design. Closing a Loadcase 

Select the tab of the loadcase you wish to close in the Loadcase window



Select File | Close Load Case

Adding and Deleting Loads

To add an extra load to the loadcase, 

Select Add Load from the Edit menu or press Ctrl+A.

A new load will be inserted into the table above the currently selected row. You can repeat this process for as many loads as you wish. If you want to remove a load from the table, simply click anywhere in the row you want to remove, and choose Delete Load from the Edit menu (or highlight the complete row by clicking the grey cell to the left of the row and press the Delete key). If you wish to delete several loads simultaneously, click and drag so that all of the loading rows that you wish to delete are selected, then select Delete Load. Editing Loads

Click on the cell containing the load name and type in a name for this load, for example "Lightship", and press the Tab key to go to the next column in the table (or simply click directly in the cell you wish to edit).

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For each item in the list you can specify a quantity. This is used to calculate the total weight of that item. For example: if the item was “crew” with a weight per unit, you could specify the quantity and unit weight, and the total weight of crew would be automatically calculated. The weight of each item should be entered in the next column. The weight must always be positive. If for some reason you wish to have an upward (negative) load, you can do so by entering a negative quantity – this can be useful if you want to apply a pure moment to the model by applying equal magnitude, but opposite sign loads to the vessel in the loadcase. Tab to the next column and enter the horizontal lever for the item. After you type in this number, press enter and the total LCG will be automatically re-calculated and displayed in the bottom row of the table. The CG position will also be shown and updated in the View windows if Large Angle Stability, Longitudinal Strength or Equilibrium analysis are selected. Note: Levers, as with all other measurements in Maxsurf Stability, are measured from the Zero Point. Loadcase Sorting

A number of tools are available for controlling the order in which items and tanks occur in the loadcase. You may move selected items and tanks up and down in the loadcase; you may also sort selected items by name, fluid type (for tanks) etc.

Insert row | Delete row | Sort rows | Move row(s) up | Move row(s) down

Sort selected columns

After moving loads, subtotals and subsubtotals, you may have to use Analysis | Update Loadcase ( button) to update the subtotals and subsubtotals. To ensure data consistency, Maxsurf Stability does this automatically prior to running an analysis. Loadcase Formatting

Maxsurf Stability allows you to improve the presentation of the Load Case window by adding blank, heading or sub-total lines in the table. Adding Component or Heading Lines Components or headings can be included in a load case by preceding the text with a period (.) character.

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Adding Blank Lines A blank line can be added into the load case by placing a dollar ($), apostrophe (‘) or full-stop(.) character in the Item Name field. Adding Totals or Subtotals A subtotal can be displayed for several loads within a load case. To do this the item name field must commence with the word ‘total’ or ‘subtotal’. Sub-subtotals Sub-sub-totals may also be inserted. Sub-subtotals must start with the text “subsubtotal”. Grouping Similar Tanks Use the move items UP or Down commands in the Edit menu to adjust the row order in the loadcase. Quantity and Unit mass for sub total rows

If a sub total includes only tanks, then the quantity and unit mass items will be included. The unit mass is the sum of all the masses of the full tanks and the quantity is the sum of the masses divided by the sum of the full tank masses. When tanks are grouped by fluid type this can be useful for calculating the total tank capacity for that fluid type.

Loadcase Colour Formatting

Different colours can be defined for fixed mass items and tanks; alternatively, tanks may be displayed in the same colour as the fluid they contain (As defined in Analysis | Fluids dialog). 

View | Colours and lines menu when Loadcase window is frontmost

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Loadcase format

It is possible to select which columns are displayed in the loadcase window. Use the Display | Data Format dialog:

The Relative density and Fluid Type which allow you to override the default tank densities as defined for each tank in the Compartment Definition window. This can be useful for vessels such as product carriers which may have cargos of different types of fluids with different densities. Moment columns (mass * lever) can be displayed if desired. Longitudinally Distributed Loads

Distributed loads can be entered in the Loadcase window in the aft limit and forward limit cells. The aft limit and forward limit columns only appear when Longitudinal Strength analysis is selected and the distributed loads will only have an effect on the results in this analysis mode. The “Long. Arm” column defines the longitudinal position of the centre of the load; the fore and aft limits define the longitudinal extents of the load.

If the longitudinal arm is changed in the Loadcase window, the forward and aft limits will be moved by the same amount. For an evenly distributed load, the centre of gravity should be midway between the forward and aft limits.

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Evenly distributed loads. Red = green and divided in the centre.

For trapezium shaped distributed loads the centre of gravity is not midway between the boundaries, but within the middle third 1/3 of the centre.

Trapezium shaped distributed load. Red = Green divided within middle 1/3 of centre.

Note: Since the load is distributed as a trapezium, the centre of gravity should lie within the middle third between the forward and aft limits of the load, at these extrema, the load distribution becomes triangular. Tanks will be automatically treated as distributed loads for the longitudinal strength calculations. Tank Loads

When you create tanks using the compartment definition, they will be automatically included in the loadcases (but not in Loadgroups which do not contain tanks). Page 51

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Tanks have a quantity value, expressed as a percentage of the full capacity and a weight column. Tank level can be given as either a percentage of full capacity, volume, a sounding or a weight.

The tank Unit Mass is the tanks mass at 100% filling.

When a tank is changed in the Compartment definition table, question marks may be shown in the loadcase momentarily while the tank’s new volumetric properties are being calculated. To update the loadcase for changes in tank loads, select Update Loadcase from the Analysis menu or toolbar.

Updating tank values in the loadcase

Irrespective of whether you have updated the values in the Loadcase Condition, the Loadcase will be automatically updated as the first step of any analysis using the Loadcase information. Also see: Update Loadcase on page 254 Loadcase cross-referencing; Loadgroups

It is possible to cross-reference one loadcase from another. This is useful if you wish to define a detailed lightship mass distribution but do not want to have it displayed in full in each loadcase. It also means that this lightship mass distribution would only need to be defined and edited in one location instead of in each loadcase. To prevent the problems of recursively including the same loadcase and also prevent tanks from being included more than once, we have defined the following rules:  A special type of Loadcase called a Loadgroup has been defined.  A Loadgroup does not contain tanks  Only a Loadgroup can be referenced  Only a Loadcase can reference a Loadgroup.  A Loadcase can reference any number of Loadgroups  A Loadgroup is referenced in a Loadcase by typing the name of the Loadgroup to be referenced in the Item column

 You can factor the referenced Loadgroup by changing the value of the Quantity column in the Loadcase.

 Loadgroups may be analysed in the same way as Loadcases – but remember the tanks are implicitly empty in a Loadgroup.

For the example above this means that the lightship mass distribution would be defined as a Loadgroup and then this Loadgroup could be referenced in any number of loadcases. The Loadcase properties dialog (Case menu) is used to define a loadcase as a Loadgroup:

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This lightship Loadgroup contains the lightship mass distribution along the ship. The Lightship load group can then be cross-referenced into any loadcase

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The referenced Loadgroup is automatically calculated and the appropriate values included in the Loadcase:

Note: Loadgroup naming The cross-referencing of loadgroups in a loadcase is case insensitive. Loadcase density override

It is now possible to override the default tank fluid densities as defined in the Compartment definition window. This allows you to load the same tanks with different fluids in different Loadcases – as might be the case for a product carrier, for instance. By default use tank defined densities:

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Type in a valid (>0.0) specific gravity and it will override the tank value:

Type in any string that doesn’t begin with an “L” for the fluid and it will revert back to the tank value:

Type in some thing that begins with an “L” and it will revert back to the “Private” density of the loadcase item.

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Free surface correction

If the corrected VCG fluid option has been chosen, the Loadcase will sum the free surface moments, divide by the total displacement to obtain the VCG correction and adjust the VCG accordingly to obtain the corrected fluid VCG. Fluid simulation If the Fluid simulation option is selected in the analysis menu, no correction is made to the upright VCG. Instead, at every step of the analysis, Maxsurf Stability calculates the actual position of the fluid in the tanks taking into account heel and trim, making the tanks’ free-surface parallel to the sea surface, thus the actual vessel CG is recalculated accounting exactly for the static shift of the fluids in slack tanks. When the corrected VCG method is selected in the analysis menu, it is possible to choose the type of free surface moment to be applied for each tank in a Maxsurf Stability Loadcase. The options available are Maximum Maxsurf Stability will use the maximum free surface moment of the tank in upright condition for all fluid levels. Actual Maxsurf Stability uses the free surface moment for the current fluid level of the tank in upright condition. IMO Maxsurf Stability uses IMO MSC75.(69) Ch 3.3 for the calculation of the free surface moment. This method approximates the movement of fluid due to heeling and is based on the fluid shift in a 50% full rectangular, box-shaped-tank. For other shapes and fillings of tanks it will not correctly approximate the free surface moment. User specified A user specified value is used for all levels and heel angles. Workshop structure

Workshop can save a Loadgroup that contains the masses of all the structural parts. This can be loaded into Maxsurf Stability and referenced in any Loadcase. Auto ballasting

Auto ballasting is a tool which facilitates adjusting a Loadcase to give a desired vessel draught, trim and heel. This command allows users to select up to eight tanks who’s fluid levels will be varied automatically to obtain a loadcase which approximately matches the vessel hydrostatics at the specified draught, trim and heel. First ensure that the loadcase window is at the front and then that the “Auto ballast” column is visible in the loadcase (Display | Data format dialog):

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Ensure “Ballasting” column is visible for automatically ballasting the Loadcase

Now, in the Loadcase, select the tanks that may have their filling levels varied. Do this by typing “auto” in the “Ballasting” column (auto complete is used, so just “A” is sufficient). You may select at most 8 tanks to be varied, but in practice, it is best to manually adjust as many tanks as possible and then use the automatic ballasting to set just the last few tanks to the required level. This is because there are multiple combinations of filling levels which will give the desired vessel attitude; however in the automatic ballasting, no attempt is made to lower the centre of gravity or minimise the bending moment is made – simply the best solution that the software can find is given.

Select those tanks whose levels can be automatically adjusted.

Finally in the Case | Auto Ballast dialog you can specify the draught, trim and heel required for the vessel. Note that the untrimmed LCG and LCB are matched which means that if trim has been specified, there will be difference between the equilibrium vessel condition and the specified trim due to the vertical separation of CG and CB.

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Specification of the vessel condition to be matched by the Auto Ballast command

When completed, an additional row will be shown at the bottom of the loadcase, this shows the target displacement and CB of the vessel at the condition specified in the Auto Ballast dialog.

Target displacement and CG is displayed when the Auto Ballast command is used

Note that if the desired draught cannot be obtained with the selected tanks completely full or completely empty or there are no tanks selected for Auto Ballasting, you will receive an appropriate warning. In some cases, a solution may not be found, try changing the Auto Ballast tanks and recomputing. When a solution has been found, a dialog is displayed which confirms the required and actual displacement, LCG and TCG; the error tolerances are based on those defined in the Edit | Preferences dialog.

Confirmation of Auto-Ballasting results

If there are errors, these will be highlighted in red in the loadcase “Target disp.” row:

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Warning when Auto-Ballasting cannot achieve required values

Modelling Compartments

This section will describe in detail how to model different types of tanks and compartments. Besides a general explanation on how to model tanks using the compartment definition table, this section contains a number of important sections that the user should be aware off when modelling tanks:  Number of Sections in Tanks on page 76  Tank and Compartment Permeability on page 67 Creating a Compartment definition file (.htk) 



Select the Compartment Definition table by clicking on the Compartment Definition tab at the bottom of the Input window. Select New Compartment Definition from the File menu

This will give you a new set of compartment definitions with one default tank. Adding and Deleting Compartments

Before you can start adding compartments, make sure you have created a Compartment definition file, see above. Compartments may be added or deleted by 

Select Add or Delete Compartment from the Edit menu.

Add will add a tank after the currently selected compartment and Delete will delete the currently selected compartment(s). The accelerator keys Ctrl+A and the Delete key may also be used to add and delete entries respectively.

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Modelling Box Shape Tanks

Simple tanks and compartments are created by specifying six values that define a boxshaped boundary for the tank. This box will be called the Boundary Box. The boundary box is made up of the fore and aft extremities of the tank, the top and bottom, and the port and starboard limits of the tank. Each value defines one of the six planes of the tank. The column headings in the Compartment Definition table include terms such as 'F Bottom, 'A Top', 'F Port' and 'A Starboard'. The 'F' and 'A' abbreviations stand for Forward and Aft, in other words the two ends of the compartment. You will notice that aft columns contain the word "ditto". This means that the value is identical at the aft end of the tank to the forward end, resulting in a parallel tank. When the “Update Loadcase” command from the Analysis menu is used, or an analysis started, Maxsurf Stability will form the sections that define the tanks and compartments. This is done by finding the intersection of the tank bounding box and the hull. Thus it is not necessary to make the tanks fit the hull manually – this is done automatically by Maxsurf Stability.

Box shaped compartments can be formed from the numerical values in the compartment definition table.

See Longitudinal Extents of Boundary Box on page 76 for some recommendations regarding setting the boundary box. Modelling Tapered Tanks

The default is for compartments to have parallel sides. If you wish to define tapered compartments, it is possible to enter different transverse and vertical values for the points defining the forward and aft ends of the compartment. If a different value is entered in one of the “ditto” columns, a tapered tank will result. Tanks can be tapered or sloped in Plan or Profile views. Maxsurf Stability does not have a mechanism for creating a sloped tank boundary in the Body Plan view.

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By changing the “ditto”-input fields, tapered tanks can be formed

Note: Tapering can be done in Plan and in Profile view. Tapered tanks in Body Plan view have to be created using a boundary surface. See Modelling Tanks Using Boundary Surfaces on page 62. Linked Tanks

Tanks and compartments may be linked. This means that although they are defined as separate tanks, they act as a single tank with a common free surface. To link tanks, compartments or non-buoyant volumes, first make them the same type as the parent and give them the same name. The easiest way to do this is to copy and paste the name from the Name column of the parent row into the Name column of the linked tank row. They may then be linked to the parent by typing l or linked in the Type column. Linked tanks and compartments do not have to be physically linked in space. However, the fluid in a linked tank or damaged compartment is always assumed to be able to flow freely between the linked volumes.

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Modelling Tanks Using Boundary Surfaces

Tanks, compartments and non-buoyant volumes may have their boundaries defined by surfaces as well as being constrained to particular dimensions. This allows for the modelling of arbitrarily shaped tanks.

Forming tanks using boundary surfaces

The surfaces to be used to define the tank boundaries are selected by clicking in the Boundary Surfaces column in the middle of the Compartments Definition table. A dialog will appear that allows you to select which surfaces form the boundary of the tank. If a tank uses boundary surfaces, the cell in the Boundary Surfaces column is coloured blue.

If you wish to use a Maxsurf surface to define a tank or compartment, tick next to the surface name in the Boundary Surface list. Note that symmetrical surfaces appear twice as there will be a starboard and a port side copy of the surface. The Starboard surface is first in the list and the Port surface second. The port surface is also identified with the suffix (P) after the name.

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Note: Only internal structure surfaces appear in the boundary surfaces list. Symmetrical surfaces are duplicated, with the port-side surface having “(P)” appended to the surface name. After selecting the internal surfaces, it is necessary to type in the extents of the boundary box. Maxsurf Stability will automatically set the “Fore” and “Aft” limits of the boundary box to just within the longitudinal limits of the Boundary Surface. This ensures that at least 12 sections are inserted in the tank. A short-cut way of creating a tank from a set of boundary surfaces is to select the required surfaces in the Assembly tree and select “Create Tank from Surfaces” in the right-click popup menu:

Create Tank from (selected) Surfaces using the Assembly tree

Also see: Forming Compartments on page 70 Number of Sections in Tanks on page 76 Longitudinal Extents of Boundary Box on page 76 Modelling External Tanks

External tanks may not be modelled in Maxsurf Stability. However, it is normally possible to add "Hull" surfaces in the Maxsurf model, which will enclose the external tanks. The tanks can then be modelled in Maxsurf Stability.

Additional box-shaped hull surfaces used to define deck tanks

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Modelling Non-Buoyant Volumes

Non-buoyant volumes are effectively permanently flooded compartments. These parts of the hull can normally be modelled using trimmed hull surfaces. However, there are occasions where it is more convenient to use non-buoyant volumes. In some cases, where the volume to be flooded forms sections within the hydrostatic section, this is the only option, e.g. waterjet ducts. The choice whether to use trimmed surfaces or nonbuoyant volumes is primarily determined by the length of the non-buoyant volume relative to the length of the vessel. Using trimmed hull surfaces When the length of the non-buoyant volume, relative to the length of the model, is large enough; the non-buoyant volume can be calculated accurately from the hull sections. If possible, trimmed surfaces should be used. The picture below is a good example of when to use trimmed surfaces.

Propeller tunnels modelled with trimming surfaces

Using tank type: Non-buoyant volume In some cases using trimmed surfaces is just not possible. For example, when the sections of the non-buoyant volume are entirely enclosed within the hull sections (as is the case for a water jet duct) the use of a non-buoyant volume is the only way in which these features can be modelled.

Water-jet ducts modelled as non-buoyant volumes

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Another occasion when non-buoyant volumes should be used, is when the length of the compartment relative to the length of the hull is too small to calculate its volume from the hull sections. A good example of this is a bow thruster on a long ship. If the vessel is very long, and the thruster duct is of small diameter, there may not be sufficient sections to model it accurately (even if you use the maximum of 200 sections for the Maxsurf Stability model). In this case you are better off modelling the thruster duct as internal structure and using these surfaces to define a non-buoyant volume. For example: in the image below the bow thruster volume is only calculated with one section.

For more information, see Number of Sections in Tanks on page 76. Tip: Besides increasing the number of sections through the bow thruster from 1 to 12, modelling the thruster duct as a non-buoyant volume has the additional advantage of being able to specify a Tank and Compartment Permeability, and hence also account for the thruster.

Bow thruster tube modelled as two non-buoyant volumes Tanks within Compartments

When a tank is defined within a compartment, Maxsurf Stability will automatically deduct the volume of the tank from the compartment volume using a “linked neg. (negative) compartment”. This is necessary for damage cases where the compartment is flooded and the volume of the tank should be treated completely separately from the compartment. Linked negative compartments are deleted and recreated whenever a tank or compartment is added, deleted or modified. Negatively linked compartments are displayed on the bottom of the Compartment Definition table solely for reference purposes and are not under direct user control. This means that linked negative compartments cannot be added, deleted or modified. Page 65

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Linked negative compartments are named based on both the parent compartment as well as the tank from which the linked negative compartment was derived. For example a linked negative compartment might be named “Compartment3 (Stbd Hydr Oil)” to reflect that it is derived from the intersection of Compartment3 with the Stbd Hydr Oil tank. Tanks Overlapping

As mentioned earlier in this manual, only compartments and non buoyant volumes or tanks can overlap with each other. Tanks or compartments of the same type (eg two tanks) can not overlap. A tank and a non-buoyant volume are also not allowed to overlap. Maxsurf Stability will first try to form tank sections and then check whether these sections overlap tank sections of adjacent tanks. When two conflicting or overlapping tanks or compartments are detected during the forming process, you will receive an error message:

Notice that the compartment definition row number of the tank is given in brackets i.e. tank #8 intersects tank #3.

Troubleshooting Overlapping Tanks Sometimes the reason for the conflict can be quite simple: eg an overlapping boundary box. However, when you are modelling tanks using boundary surfaces, the surface boundaries act as a boundary between two adjacent tanks and the bounding box extents are allowed to overlap. In these cases, it can be quite difficult to see why the tanks overlap, especially if you have a large number of tanks already defined.

By temporarily deleting all tanks except for the one that does not form, it often becomes clear why the tank overlaps. In the case of the image above, the tank’s fwd most section goes all the way to the CL (probably because the fwd boundary box extent is just fwd of the boundary surfaces or exactly on the edge of a boundary surface). This causes this particular tank to “overlap” with surrounding tanks. Page 66

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Procedure to Fix Overlapping Tanks: 

Save Model



Go into Comp def window



Save comp def



Delete all tanks except for one you wish to investigate



form tanks, inspect tank sections



Try to fix tank definition, eg by selecting additional boundary surfaces

Now that you know how to fix it.. 

Close comp def file. Do NOT save!!



Open saved Comp def file



Fix compartment.



Save & move on to next compartment.

Tank and Compartment Permeability

Tanks may have two permeabilities; one, which is used when the tank is intact, and the other when it is damaged. Compartments and non-buoyant volumes have only one permeability, thought it is listed in both columns. The compartment permeability is applied when the compartment is flooded in a damage condition and the non-buoyant volume permeability is applied at all times since it is always flooded. In the case of damaged tanks and compartments, the permeability fraction is also applied to the free-surface-moment contribution of that tank or compartment. Permeability of Compartments As opposed to tanks, compartments typically have structure (other than plate stiffeners) and equipment inside. In case of large variations in permeability within a compartment it is recommended to model separate linked compartments with separate permeability to increase accuracy. For example an engine room with engines and auxiliaries at the tanktop could be divided up in a lower- and an upper engine room compartment. The lower compartment will have a permeability of, for example, 60% and the upper compartment a permeability of 95%. Depending on the level of accuracy required, the engines and equipment could also be modelled individually as empty tanks. Relative Density of Tank Fluids

Relative Density (Specific Gravity) values can be typed directly into the Relative Density column of the Compartment Definition table.

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Alternatively the fluid type can be entered into the Fluid Type column, either as the name or as one of the single letter codes (when entering the name, auto complete is used, so it is normally only necessary to type the first few letter of the name). If a fluid type is entered, the relative density value is obtained from the value specified in the Density dialog. Whenever values are changed in the Density dialog (see Density of Fluids on page 195), all entries for that fluid in the compartment definition are automatically updated. If the tank defines a cargo tank that will carry different liquid cargoes, the default density specified here in the compartment definition may be overridden in the loadcases. Tanks and Surface Thickness

If you have specified that Maxsurf Stability should include the surface thickness, the tanks, compartments and non-buoyant volumes will correctly account for the surface thickness and its projection direction: the tanks will go to the inside of the hull shell. Note: Thickness of boundary surfaces are not taken into account, hence you should design these surfaces to the inside of the tank. Compartment and Tank Ordering

The tank definition order can be adjusted in a similar way to loads in the loadcase. Select the rows you wish to use and use the Edit | Move Items Up or Down commands (there is no provision for sorting tanks alphabetically). Groups of linked tanks and compartments will be moved together. Compartment and Tank Visibility

When creating complicated tank plans, it is often useful to check individual tanks. You can either control the tank visibility through the Assembly window, or if you prefer, you can use damage cases to quickly change the display to show certain tanks.

Assembly view can be used to show and hide tanks/compartments

Using damage cases, selected tanks may be displayed in the following manner:  

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

 

Select whether you want to see the tank outline or the tank sections (tanks sections are preferable when checking that tanks have been formed correctly since it is these sections which are used to determine the tank volume and other properties). Choose the damage case from the Analysis toolbar Set any of the tanks and compartments you wish to be visible to damaged in the damage case window.

You can make the damage case window quite small and tile it next to the perspective view. Use this to quickly turn tanks on and off by changing their damage status.

Using a damage case to quickly change the tank and compartment visibility Compartment and Tank Display Options

Tanks may be displayed with a transparent, shaded representation of the fluid-plane in the tank (or floodwater plane in the case of a damaged compartment) and/or with a crosshatch of the tank extremities. The shaded fluid level is shown in the Plan and Perspective views only. The tank-filling levels are taken from the currently selected loadcase.

Shaded tank fluid-planes

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Shading of damaged floodwater-planes

Tank cross-hatching in Plan and Profile views

Tank sections

When in Tank Calibration mode, tank sections are also displayed in the Bodyplan view when the “Show single section” option is selected. Only tank sections that lie on or near the current station are shown – this makes it easier to verify that the tanks have been formed.

Forming Compartments

Tanks and compartments are formed automatically by Maxsurf Stability (once the tank extents and any boundary surfaces have been defined) by selecting Recalculate Tanks and Compartments from the Analysis menu. The formed status of a tank (yes or no) is shown in the last column of the compartment definition table. Page 70

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This section describes the internal tank-forming process that Maxsurf Stability uses to form tanks. First a step-by-step outline of the tank forming process is given, followed by the tank section insertion process. Understanding these processes may assist you in rare situations where the tank forming does not work as expected. Step-by-Step Tank Forming Process

As an example, the starboard waterballast tank below will be created using boundary surfaces.

An example of a port and starboard waterballast tank with a pipe tunnel at the centreline. The water ballast tanks have a margin plate on the side.

Maxsurf Stability uses three input items to form the compartment  Boundary surfaces (if defined)  Boundary box  Maxsurf Stability Hull sections

Starting position The starboard tank margin plate is modelled using an Internal Structure surface from Maxsurf.

Starting point: Maxsurf Stability Hull sections with an internal surface and a bounding box

Also see: Modelling Tanks Using Boundary Surfaces on page 62 and the Maxsurf manual on internal structure surfaces

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Step 1: Close Internal Structure Surface

Maxsurf Stability will close the Internal Structure Surface contour by drawing a straight line between the ends of the opening.

Maxsurf Stability uses the same method for forming the tank section from the boundary surfaces as for forming the hydrostatic sections through the hull. As with the hull sections, the surfaces selected to form the tank boundary must form closed section contours at all longitudinal positions through the tank. The area inside the selected surfaces will define the tank contour. Make sure that the boundary surfaces:  Form a closed section contour, or  There is no more than one opening – the opening will be closed with a straight line

Note: Maxsurf Stability will close the section contour of the selected boundary surfaces only. Often a tank is not formed as expected because only one side of the internal structure surface was selected for example the portside (p). Another common cause of unexpected results is trimming. If you selected “use trimmed surfaces” while opening the Maxsurf model, Maxsurf Stability will use the trimmed internal structure surface. Usually the internal structure surfaces are best to be left untrimmed. Step 2: Clip to Boundary Surface Using the closed surface section contour Maxsurf Stability can now form a closed compartment section. The tank or compartment looks like this at this stage:

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Step 3: Clip to Hull Maxsurf Stability will clip the compartment section to the hull.

Step 4: Clip to Boundary Box Finally the compartment section is clipped to the boundary box. The boundary box is formed from the numerical input in the Compartment definition table.

More realistic surface-bounded tanks

Whilst the above example shows the principles by which surface-bounded tanks are formed, it is not really realistic because it would not be possible to define a tank above the surface-bounded double bottom tanks. In practice additional surfaces would be required. A more realistic example is shown in the following section. In this example the vessel has both wing and double bottom tanks with non-rectangular cross-sections thus requiring them to be defined by boundary surfaces – see blow:

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Sketch of tank cross-sections

Five surfaces have been defined to define the tank boundaries:

Tank Boundary surfaces defined in Maxsurf

The following surfaces need to be selected for the different tanks so that closed sections are generated (or at most one section) Hold (C) TankWing, TankWing (P), TankTop, TankTop (P) Double Bottom (P) TankTop (P), BottomClosure (P), TankBilgePlate (P) Double Bottom (S) TankTop (S), BottomClosure (S), TankBilgePlate (S) Wing Ballast (P) TankWing (P), OuterClosure (P), TankBilgePlate (P) Wing Ballast (S) TankWing (S), OuterClosure (S), TankBilgePlate (S)

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Maxsurf Stability tank definition

Surfaces for Hold (C) (top is closed automatically)

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Surfaces for double bottom tanks

Surfaces for wing tanks (top is closed automatically)

Number of Sections in Tanks

The volume of a tank or compartments is calculated by integrating section properties along the length of the tank. Thus it is important to have a sufficiently large number of sections to accurately model the tank. Maxsurf Stability will normally place twelve sections between the forward and aft limits defining the tank. If this results in a section spacing greater than the spacing for the hull spacing, additional sections will be inserted into the tank so that the tank section spacing match the hull section spacing. Also see Longitudinal Extents of Boundary Box on page 76 Longitudinal Extents of Boundary Box

For tanks near the ship’s extremities it is good practise to set the “Fore” and “Aft” limits in the compartment table to just inside the hull surface (say 1mm). In most cases, this will be done automatically by Maxsurf Stability. The following example illustrates why: Page 76

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 If the boundary box is set like this:

The number of hull sections is dependent on the section spacing in the model.

 But if the boundary box is set just inside the forward limit of the bulbous bow:

To recap – Near the ship’s extremities, the longitudinal extents should not be set to extreme values, they should be set to just inside the extents of the hull surfaces to ensure that at least 12 sections are used to calculate the tank volumes. For internal structure surfaces that are used as boundary surface, Maxsurf Stability will automatically set the “Fore” and “Aft” limits of the boundary box to just within the longitudinal limits of the boundary surface. This ensures that at least 12 sections are inserted in the tank. Note that transversely and vertically there are no such restrictions. Also see Number of Sections in Tanks on page 76 Forming Compartments on page 70 Compartment Types

Five compartment types can be created using the Compartment Definition table - tanks, linked tanks, compartments, linked compartments and non-buoyant volumes.

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Tanks Will be included in the tank calibration output and are automatically added to the loadcase. Linked Tanks Will have their volume added to the parent tank with the same tank name. They do not have a separate entry in the loadcase. In addition, if a tank is damaged, any tank that it is linked to will also be regarded as damaged. Tanks need not be adjoining to be linked, they can be remote from one another. In this case the tank linking simulates tanks with cross connections. Compartments Are only used to specify compartmentation for damage. They are not included in the tank calibration output and will not be added to the loadcase. Linked Compartments Work in the same way as linked tanks. This allows you to damage a complex compartment configuration by linking compartments together and damaging the parent compartment. Non-Buoyant Volumes Are only used to specify compartments of the vessel which are permanently flooded up to the static waterline. They are ideal for defining water-jet ducts, moon pools, etc. and essentially behave as damaged compartments. They are not included in the tank calibration output and will not be added to the loadcase. To change the type of a tank, type the first character of the tank type (t, c or n) in the Type column of the Compartment Definition table and then press Enter. This will automatically set the tank/compartment to the correct type. Sounding Pipes

Maxsurf Stability allows sounding pipes to be defined for each tank. One sounding pipe per tank is permitted and up to nine vertices per sounding pipe, allowing inclined, bent or curved sounding pipes to be modelled. Maxsurf Stability creates a default sounding pipe when the tank is formed (either by running an analysis, or using one of the following commands: Analysis | Recalculate Tanks and Compartments; or Analysis | Update Loadcase. The default sounding pipe is placed at the longitudinal and transverse position of the lowest point of the tank. If the lowest point of the tank is shared between several locations (e.g. the bottom of the tank is flat either longitudinally or transversely) the default sounding pipe location is placed at the aft-most low point and as close to the centreline as possible. The top of the sounding pipe is taken to be level with the highest point of the tank and the default sounding pipe is assumed to be straight and vertical. Automatically created sounding pipes will be recalculated if the tank geometry changes. However, once the sounding pipe has been edited manually, any changes to the sounding pipe due to tank geometry changes will also have to be made manually. Edit Sounding Pipes

To customise a sounding pipe, you need to use the Sounding Pipes table in the Input window, shown below.

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You can activate this window by selecting from the Windows | Input | Sounding Pipes menu, by clicking on the tabs at the bottom of the Input window, or by clicking on the icon in the window toolbar. To add vertices to create a bent sounding pipe, make the sounding pipe type User Defined, then click on the first row of a particular sounding pipe and choose Edit | Add or use the Ctrl+A key combination. A new row will be added to the sounding pipe and the longitudinal position, offset and height of the vertex can be edited. Unwanted vertices can be deleted by clicking on the relevant row in the table and selecting Edit | Delete or by hitting the Delete key. Note that each successive vertex in a sounding pipe must be no higher than the previous vertex i.e. it is not acceptable to have S-bends in the sounding pipes. Calibration Increment

Maxsurf Stability allows user definable increments (or: intervals) for tank soundings. This is done by specifying a numerical value for the increment for each tank in the Calibration Spacing column of the Sounding Pipes Input window.



Type the value of the desired calibration increment in the Calibration Spacing cell for the tank calibration you wish to modify.

If no increment is entered, Maxsurf Stability uses its default value based on a reasonable division of the depth of the tank. In this case the Sounding Pipes table will display “Auto” in the Calibration Increment column for the tank.

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Note Increments are measured along the sounding pipe, not along the vertical axis of the tank. If the sounding pipe is inclined or if it has multiple angles, soundings will step evenly along the inclined length of the sounding pipe. Damage Case Definition

In all but the floodable length and tank calibration analysis modes, Maxsurf Stability is capable of including the effects of user-defined damage. Maxsurf Stability allows the user to set up a number of damage cases. Volumes that are permanently flooded should be defined as non-buoyant volumes. Adding a Damage Case

To add a damage case, make the Damage window active and select Add Damage Case from the Case menu. You may specify a name for the Damage Case in the dialog. Each new damage case will have a column in the Damage Window and a tick may be placed to indicate which tanks and compartments are damaged for that particular Damage Case. The new damage case is added after the currently selected damage case column, to insert a damage case immediately after the intact case, select the intact case column. Several damage cases may be added in one go by selecting a number of columns.

Damage case specification (normal view)

When Water on Deck (WoD) has been selected, the Damage Case window changes and allows the specification of there parameters required for WoD. Editing the extents of damage will not update the damaged condition of the tanks and compartments (this is done only if the damage extents are set through the Case|Extent of Damage dialog).

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Enhanced Damage window when WoD analysis is selected Deleting a Damage Case

To delete damage cases, simply select the columns to be deleted in the Damage Window and select Delete Damage Case from the Case menu. Note that it is not possible to delete the intact case. Renaming a Damage Case

The name of the current damage case may be changed by selecting Edit Damage Case when the damage case window is active, the current damage case is selected from the Analysis toolbar – see below. Re-ordering a Damage Case

Damage cases can be re-ordered by clicking in the damage cases you wish to move (a single case or several adjacent cases). Then click on the Edit Left / Right toolbar buttons to move the selected damage case(s) left or right. Note that the intact case cannot be moved.

Selecting a Damage Case

The current damage case is selected from the Analysis toolbar.

The Loadcase and View windows will reflect the damage defined in the current damage case. To perform analyses for the intact vessel, select Intact as the current damage case. Any subsequent analyses will take into account the damaged compartments. Note that carrying out a Tank Calibration analysis will force the intact case to be selected. This is also the case for the Floodable Length analysis which effectively sets up its own longitudinal extent of damage. Page 81

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When tanks have been damaged, their weights and levers are no longer displayed in the Loadcase window and the word ‘Damage’ is displayed in the quantity column. This is because Maxsurf Stability uses the “Lost buoyancy” method rather than “Added mass”. Note: Maxsurf Stability uses the “Lost buoyancy” method rather than “Added mass”. Flooding is considered to be instantaneous up to sea level. Any tank fluids are treated as having been completely replaced by seawater up to the equilibrium waterline. Maxsurf Stability assumes that all compartment definition has been done after the tanks have been defined. If you have linked tanks or compartments or added tanks within compartments after the definition of a damage case, you should toggle the damage status of the damaged tanks. This is simply done by copying all the damage case data to a spread sheet, turning off all damage in all the damage cases (use the fill down command) and then pasting back in the original data from where it was stored in the spreadsheet. Displaying Damage Cases

When a damage case is selected, all damaged tanks and compartments will be displayed in damaged tank or damaged compartment colour respectively. These colours can be specified in the View | Colours and lines menu. In the Loadcase Window damaged tanks are displayed with the label 'Damaged' in the Quantity column, and all values set to zero.

The Loadcase Window displays damaged tanks and excludes them from any calculations.

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Extent of Damage Cases

The damaged compartments can automatically be set by using the Case | Extent of damage command. Select the column of the damage case you wish to specify the extent of damage for and choose Extent of Damage from the case menu:

Defining the damaged compartments by specify the extent of damage.

Specify the extent of the damage – any tanks or compartments that lie partially or wholly within the extent of damage will be automatically flagged as damaged:

Automatically generated damage case from using Extent of Damage command.

The volume of seawater in damaged tanks can be seen in the Compartments table in the window.

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Cargo dropout

It is possible to select whether cargo is lost or retained in damaged cargo tanks: Case | Empty Damaged Tanks menu.

In the case where “Empty Damaged Tanks” is selected, cargo is removed from damaged tanks (as was the case with all previous versions of Maxsurf Stability). Now damaged tanks are highlighted in Red in the Loadcase table:

However, if the option to Empty Damaged Tanks is turned off, the cargo masses of the damaged tanks will be retained in the loadcase, but will be highlighted in red to indicate that they are also damaged

If the “Simulate fluid movement” option is selected, the cargo in the damaged tanks will be shifted as the vessel heels and trims to maintain the cargo waterline parallel to the sea waterline, as would be the case for the intact vessel.

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Damage Analysis and Partial Flooding

To help clarify the way that Hydromax works, a number of terms are defined in the following sections. Room

A room is any space defined in the Compartment definition table in Hydromax. Normally a Tank or a Compartment (but may also include a Non-Buoyant Volume – NBV). Fluid simulation

In Hydromax fluid cargos in tanks can be modelled exactly. That is for any orientation (heel and trim) of the vessel, the fluid level in tanks is always parallel to the external sea surface. Whilst keeping the fluid level parallel to the external sea-surface, the height is iterated so that the volume in the tank matches the volume specified in the Loadcase. This simulates the quasi-static movement of the cargo fluids in tanks; thus at a specified vessel orientation, the actual quasi-static centre of gravity is calculated, hence the righting moment can be calculated directly without adjustment. This analysis option is known as “Simulate fluid movement”:

Analysis | Fluids dialog Lost-buoyancy method for damage analysis

The lost-buoyancy method for damage stability is always used in Hydromax. That is, flooded portions of the hull are removed from the intact buoyant volume of the hull envelope. The same method is used for Non-buoyant volumes (which are essentially permanently flooded spaces). It is quite easy to visualise this method for fully-flooded spaces (i.e. spaces that are either completely flooded or flooded up to the external seawaterline). However, the same principles, of removing flooded spaces from the intact hull, can be applied to partial flooding. In this case, the top of the lost-buoyancy volume (damaged space) is a waterline parallel to, but below the external sea-waterline. Because the lost-buoyancy waterline is always parallel to the external sea-waterline, the centre of the lost-buoyancy moves as the vessel orientation changes (in a similar way to the fluid simulation of filled tanks). Added mass method for damage analysis

In contract to the lost-buoyancy method, the added-mass method adds floodwater to the damaged rooms. In fact if a quasi-static fluid-simulation method (as described above) is applied to the floodwater the righting moment calculated by both lost-buoyancy and added-mass methods are the same. However, because the vessel displacement is different, the righting arm (GZ) is different for both methods. Page 85

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Hydromax does not use the added-mass method for damage stability. However, it is possible to simulate this manually by running an intact analysis and adding sea-water to the flooded rooms and turning on the Fluid simulation option. Care should be taken to ensure that the tank sea-water levels do not exceed the external sea-waterline; this must be done my manual iteration. Further, to flood compartments in this manner, it will be necessary to change them to Tanks so that they appear in the Loadcase. Partial flooding

Partial flooding is where the lost-buoyancy in a damaged space does not necessarily extend up to the external sea-waterline. The waterline of the lost buoyancy may be below, but never above the external sea-waterline. Thus in Hydromax, the partial flooding is specified as a maximum allowable percentage of the room which may be flooded; noting that under some circumstances, it may not be possible to achieve this level of flooding if the room is too high compared with the external sea-waterline. In Hydromax, the partial flooding is specified as percentage of the full geometric volume of the room. The geometric volume being the volume without applying a permeability. This is because: a) It allows for specification of lost buoyancy in a room for an intermediate stage even if the room is not immersed in final stage of flooding. b) The analysis is quicker because it is not necessary to compute the final stage first. c) The room capacity is known and does not change; the final stage flooded volume changes for any change in analysis condition. d) The “final stage” is not an unambiguous term. For instance during the calculation of a GZ curve, does this refer to the final stage flooding at zero heel, equilibrium heel or at each heel angle for which the GZ curve is calculated? e) The resulting flooded lost buoyancy data are available as results, thus it is possible to specify as a percentage of final flooded volume if required. f) Because Hydromax has intact and damaged permeabilities for tanks, it was felt to be less confusing simply to use the geometric volume. Constant displacement

Constant displacement is sometimes taken to mean Lost buoyancy (as defined above); however in Hydromax, constant displacement is taken to mean that the Loadcase does not change under damage, and refers as to whether or not liquid cargo in damaged tanks should be left in, or removed from the Loadcase. In fact previous versions of Hydromax always removed the liquid cargo of damaged tanks from the Loadcase, resulting in a lighter displacement for the damaged vessel (i.e. constant displacement was not being used). In version 18 of Hydromax a switch has been included and the constant displacement method can now be used if desired (turn off the “Empty damaged tanks” option in the Case menu):

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Variable or constant displacement options for the damaged Loadcase

Partial Flooding – Modelling and Analysis

Partial flooding is available in Maxsurf Stability Enterprise (Hydromax Ultimate). It is possible to only partially flood a room in Maxsurf Stability. Partial flooding can be enabled in the Case menu.

Enable Partial Flooding

With Partial Flooding enabled (and also for Water on Deck), the Damage case list changes so that text data may be entered (rather than check boxes). Type “I” for intact rooms, “D” for damaged rooms or specify the maximum percentage of the total room volume that can be flooded:

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Specifying Partial Flooding Generating a partial case based on an existing case

If you have an existing case, it is quite simple to generate a partial case based on the damage specified by the existing case:  Add a case next to the intact case by selecting the column of the existing case and then choosing Add Damage Case from the Case menu.

 Give the new case a name and click OK in the dialog  Copy all the damage from the original case to the new one  Select the new case and choose Edit Damage Case from the Case menu.  Check the “Set flooding” option and specify the partial flooding percentage, and click OK; all the damaged tanks will now have the specified filling level:

Partially flooded room waterline

For fully damaged rooms, the lost buoyancy extends up to the external sea-waterline (or the top boundary of the room in question). In the partially flooded case, the lost buoyancy in a room does not necessarily extend all the way up to the external seawaterline. Two options are proposed: 1. All rooms defined as partially flooded in a Damage case share a common upper limit of lost buoyancy (effectively share a common flooded waterline). In this case the lost buoyancy percentage is common for all partially flooded rooms and the lost buoyancy is this percentage multiplied by the aggregate full room volumes of the partially flooded rooms. When this option is selected, all partially damaged rooms have the partial flooded percentage written in italics. Page 88

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2. All rooms defined as partially flooded in a Damage case have individual upper limits of lost buoyancy as defined by their individual maximum lost buoyancy ratios. By default, damage cases take the first option, this may be changed in the new Damage Case Properties dialog (Case | Edit Damage Case). It is also no longer necessary to select the whole damage case column to edit its properties (selection of any cell in the damage case is sufficient):

Enhanced Damage Case Properties dialog Note that:

1. The percentage specified is the percentage of the full room volume (not the percentage of the final damaged lost buoyancy). 2. The percentage specified is the maximum the room can flood, it is possible that due to the trim and heel of the vessel that the room will not flood to this level – remember that the room cannot flood above the exterior waterline. 3. As with ordinary damage cases, partial flooding cases are still treated as lost buoyancy, not as an added mass.

Here it can be seen that the lost buoyancy (red shaded areas) does not extend all the way to the external waterline (yellow line)

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Flooded results

Remember that the lost buoyancy may be found in the Compartments results table. This table now also contains the intact full volume of the compartment. For rooms made up of linked parts, the parent row shows two values: the first is the parent component only; the value in parentheses is for the sum of all the linked components. Remember that the “lost buoyancy / full volume” percentage is based on the geometric volume, that is the volume ignoring permeability. The percentage is calculated without including perrmeabilities to avoid possible confusion as to which permeability -intact or damaged- is used.

Lost buoyancy volumes reported in Compartment results table Examples

Below are shown the differences of the two waterline options: Common partially flooded waterline in all damaged rooms

In the first example the partial flooding is specified to use a common waterline. It can be seen that the damage has a common water line. In the results it can be seen that the “100 Forepeak” and “200 DB ballast No1 S” rooms exceed the damaged percentage whilst the “105 Focsle” is empty because it is above the external sea-waterline. When the total flooded volume, 2787m3, is compared with the total volume of the damaged rooms, 6130m3, the specified percentage of flooding has been achieved: 45%. (Sometimes there can be a fraction of a percent difference, this is because the floodwater level is calculated to the nearest 0.1mm, but this can still represent a large volume if the flood-waterplane is large.)

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Example 1: Common waterline Individual partially flooded waterlines in each room

In the second example the partial flooding is specified to use individual waterlines. In this case all but the “105 Focsle” are flooded to the specified percentage. The “105 Focsle” is not sufficiently immersed to achieve the specified percentage because it is not allowed to flood above the external sea-waterline.

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Example 2: Individual waterlines Batch analysis results file and Report

Because of the introduction of partial flooding, there have been some minor changes to the format of the batch analysis results file where the room damage status is listed:

New format of Batch results (shown in MS Excel for clarity)

Similarly, there have been changes to the Report; additional information is included and is tabs delimited to facilitate making into a table if so desired.

New Report format for Room damage

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Key Points (e.g. Down Flooding Points)

Key points such as downflooding points and hatch openings can be defined in Maxsurf Stability using the Key Points window. The points may be displayed in the Design View window and will be displayed in different colours depending on whether or not they are immersed. Immersed key points will be displayed in the same colour as flooded tanks or compartments. Key points may be placed asymmetrically, a positive offset is to starboard and a negative offset is to port. Vessels which have symmetrical key points on starboard and port sides must have both key points added to the table. There are several types of Key Points:  Down Flooding points  Potential Down flooding points  Embarkation points  Immersion Points

Only downflooding points are used in determining the downflooding angle, which is used in criteria evaluation. The other types of points have their freeboard measured but are not used for the evaluation of the downflooding angle and are for information only. Adding Key Points

To start adding downflooding points go to the Key Points table, select New Key Points from the File menu. You will be given a default point. To add additional key points to the table, choose Add from the Edit menu or press Ctrl+A. A new point will be inserted below the currently selected row in the table. Deleting Key Points

To delete a Key point, click anywhere in the row of the point to be deleted and select Delete. To delete more than one point at a time, click and drag over the rows you want deleted.

Select Delete from the Edit menu, and the selected rows will be deleted. Editing Key Points

Key points are defined by entering a name, a longitudinal position, a transverse offset from the centreline, and a height. Click in any cell and enter the name or value you require. All points are entered relative to the zero point. The type of Key Point may be selected from the combo-box in the Type column of the Down Flooding Points table in the Input window:

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Links to Tanks or Compartments

Downflooding points may be linked to tanks or compartments. Select the tank or compartment from the combo-box in the Linked to column of the Down Flooding Points table in the Input window:

Downflooding points that are linked to tanks or compartments, which are damaged in the currently selected damage case, will be ignored when computing the downflooding angle. These downflooding points will appear italicised and an asterisk (*) is postfixed to the downflooding point’s name in the DF Angles table of the Results window:

The downflooding angles for each of the points are displayed in the results window. The downflooding angles are computed during a large angle stability analysis; the freeboards after an Equilibrium or Specified Condition analysis. Immersed points are highlighted in red in the Freeboard column. In addition to the Key Points results, immersion angles or freeboards (depending on the analysis) are also given for the margin line and deck edge. In the Name column the longitudinal position where immersion first takes place (or the lowest freeboard) is given. Note: Linking a downflooding point to a tank does not mean that Maxsurf Stability will consider a tank damaged when the downflooding point is submerged. This form of automatic flooding is not supported in Maxsurf Stability yet.

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Margin Line Points

The margin line is used in a number of the criteria. Maxsurf Stability automatically calculates the position of the margin line 76mm below the deck edge when the hull is first read in. If necessary, the points on the margin line may be edited manually in the Margin Line Points window (the deck edge is automatically updated so that it is kept 76mm above the margin line). It is only necessary to modify the height value of the margin line points. Once this has been done for all the points that need to be changed, selecting Snap Margin Line to Hull in the Analysis menu will project all of the points horizontally onto the hull surface, ensuring that the margin line follows the hull shape precisely. Asymmetric margin lines and deck edges are not supported. Points may be added or deleted as required using the procedure described in Adding Key Points and Deleting Key Points on page 93. Modulus Points and Allowable Shears and Moments

The Modulus window can be used to enter maximum allowable shear forces and bending moments for each section. One or more points can be entered in this window. Allowable shear force and/or bending moment can be specified at each point. The modulus value is not currently used as deflections are not calculated.

To start a table of allowable shear forces and bending moments, bring the Modulus table to the front and choose New Modulus Points from the File menu with the Modulus window frontmost. The allowable values can be saved and recalled as text files by using Open and Save from the File menu. New allowable values can be inserted by selecting Add from the Edit menu and entering a longitudinal position as well as an allowable shear and/or moment. Points may be added or deleted as required using the procedure described for the key points. These allowable values are displayed as lines on the longitudinal strength graph. Floodable Length Bulkheads

Bulkheads entered in the Input window are used for Floodable Length analysis in order to optionally plot the compartment lengths in the floodable length graph for easy verification that the critical compartment lengths are not exceeded. The Bulkheads are automatically sorted by longitudinal position. For more information see Floodable Length on page 130.

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Stability Criteria

Stability criteria may be evaluated after a Large Angle Stability analysis and after an Equilibrium analysis. Stability criteria are required to perform a limiting KG and Floodable Length analysis. Please refer to Chapter 4 Stability Criteria starting at page 209 for information on defining and selecting criteria.

Analysis Types After specifying the input values and checking the Maxsurf Stability model, the analysis can be performed. In this section the different analysis types available in Maxsurf Stability will be described. The following analysis types are available in Maxsurf Stability:  Upright Hydrostatics  Large Angle Stability  Equilibrium Analysis  Specified Conditions  KN Values Analysis  Limiting KG  Floodable Length  Longitudinal Strength  Tank Calibrations  MARPOL Oil Outflow  Probabilistic Damage

Also, some general information is given on:  Starting and Stopping Analyses  Batch Analysis

The required analysis settings and environment options will be discussed separately and in more detail in the next two sections of this chapter. Following each analysis, one or more graphs may be shown – select the graph to be displayed from the pull-down menu in the Graph window. The Data Format dialog can be used to specify what is displayed in some graphs and tables; the available options depends on the current results table or graph:

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Data format dialog for Upright hydrostatics table and graph

Upright Hydrostatics

Upright hydrostatics lets you determine the hydrostatic parameters of the hull at a range of drafts, at zero or other fixed trim. Choosing Upright Hydrostatics

Select Upright Hydrostatics from the Analysis Type option in the Analysis menu or toolbar. Upright Hydrostatic Analysis Settings

The following analysis settings apply for Upright Hydrostatic Analysis:  Draft from the Analysis menu, specify range of drafts for analysis  Trim from the Analysis menu, you may specify a fixed trim for all drafts

A range of drafts for upright hydrostatic calculations can be specified using the Drafts command from the Analysis menu.

Initial and final drafts can be entered, together with the number of drafts to be used. The Vertical Centre of Gravity is also required for the calculation of GM etc (if the vessel is trimmed, the LCG also affects these measurements). When a design is first opened, the initial draft defaults to the draft at the DWL in Maxsurf. Similarly the VCG defaults to the height of the DWL.

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Upright Hydrostatics Environment Options

The following environments can be applied to the upright hydrostatics analysis:  Density from the Analysis menu  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar

Upright Hydrostatic Results

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The curves of form are shown on a separate graph and the sectional area may be show for any of the drafts: see Select View from Analysis Data on page 204. Bonjean Curve Data

Bonjean curve data is calculated as part of a standard Upright Hydrostatics Analysis. Bonjean curves are curves generated at station locations showing sectional area variation with draft. Bonjean curve data is calculated at sections and drafts according to the Design Grid station locations and waterline locations. The results are displayed in the Graph widow and the data may be accessed by double clicking the graph.

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Large Angle Stability

Large angle stability lets you determine the hydrostatic parameters of the hull at a range of heel angles either with or without trim or free-to-trim. Choosing Large Angle Stability

Select Large Angle Stability from the Analysis menu or toolbar. Large Angle Stability Settings

The following analysis settings apply for Large Angle Stability Analysis:  Displacement and Centre of Gravity using the Loadcase window  Heel from the Analysis menu, select range for analysis  Trim (fixed or free) from the Analysis menu

If criteria are being evaluated, the heel range and heel angle steps should be chosen accordingly, to ensure accurate evaluation of the criteria. Note You can select positive heel direction (port or starboard). However, you can enter negative values and test full 360 degrees of stability if you wish. Some criteria require calculations of GZ at negative heel. The criteria are only evaluated on the side of the graph that corresponds to positive heel angles. For example: when using a -180 to 180 heel range, the results may be two angles of vanishing stability, the one that would be reported in the criteria would be the one with a positive heel angle (even if the one at negative heel occurred at an angle closer to zero). Also see: Heel on page 186 in the Analysis Settings section. Large Angle Stability Environment Options

The following environments can be applied to the large angle stability analysis:  Fluid simulation of tank fluids centre of gravity  Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar  Stability Criteria  Water on Deck (WoD) – Stockholm Agreement Large Angle Stability Results

Large Angle Stability Analysis results are:

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Chapter 3 Using Stability  Hydrostatic data table for each angle of heel  GZ curve  Dynamic stability (GZ area) curve  Graph of hydrostatic parameters against heel angle  Graph of max. safe steady heel angle  Stability Criteria evaluation  Downflooding angles to key points, deck edge and margin line  Curve of areas at each heel angle

Dynamic stability Graph A graph of the GZ area integrated from upright may be plotted, features such as downflooding angle are also included on the graph. Page 101

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Curve of Areas Shows the curve of areas for the currently selected heel angle (use Display | Select view from data to chose the heel angle from the GZ results table). Large Angle stability Graph; Curves of Form; Shows the variation of hydrodynamic properties with heel angle. Graph of maximum safe steady heeling angles for sailing vessels These calculations are derived from the value of GZ at a critical heel angle, for example the angle of downflooding or angle of deck edge immersion. Once a GZ curve has been calculated, you can display the maximum safe heeling angle curves by selecting the graph type in the pull-down menu.

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The parameters for the calculation can be modified in the Display | Data Format dialog (this graph must be selected in the topmost window):

Analysis options for the calculation of Maximum steady heel angles (Display | Data Format).

The first part of the dialog is almost exactly the same as the “Angle of equilibrium - derived wind heeling arm” criterion. This allows you to specify the critical condition that should not be exceeded due to a gust or squall. MCA require downflooding but you can include additional criteria if desired. You can also change the shape of the heeling arm curve and the gust ratio.

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In the lower-left, you can specify the squall wind speeds (you can add any number) The default gives three wind speeds of 30, 45 and 60kts. Finally you can adjust the axis limits. This is because normally you will have computed a GZ curve for a wider heel range than you would wish to display in this graph – it is uncommon to sail a vessel with a steady heel angle of greater than 40 degrees. It can often be useful to duplicate this criterion in the GZ criteria that are evaluated. This will give you the same result as for the gust limiting line.

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The same safe angle of heel to prevent downflooding in the event of a gust (16.5 deg) is found.

To obtain smooth curves, the GZ curve should be calculated at small intervals of heel, especially at the lower heel angles – typically steps of 1degree. Under some circumstances, it may not be possible to evaluate the curves, the most common reason for this is that the GZ curve has not been calculated up to a sufficiently high angle of heel and downflooding angle cannot be found. Full details of the calculations can be found in: Sailing Yacht Design: Practice. ed. Claughton, Wellicome and Shenoi. Adison Wesley Longman 1998. ISBN 0-582-36857-X STABILITY INFORMATION BOOKLET available from the MCA. www.mcga.gov.uk Stability Criteria Evaluation The criteria results are displayed in the Criteria tab in the results window. For more information on how to customize the display of the criteria results, please refer to the Results Window on page 231 in the reference section. Important: For important information on varying displacement while evaluating criteria, see: Important note: heeling arm criteria dependent on displacement on page 290. Downflooding Angle After a Large Angle Stability analysis, the Key Points Data table lists the downflooding angles of the margin line, deck edge and defined Key Points. In addition, the first downflooding point is marked on the large angle stability graph. Only the positive downflooding angles are displayed, hence if there is any asymmetry, the large angle stability analysis should be carried out heeling both to starboard and to port. For the margin line and deck edge the longitudinal position at which immersion first occurred is provided.

Downflooding points that are linked to tanks or compartments that are damaged in the currently selected damage case, will be ignored when computing the downflooding angle. These downflooding points will appear italicised, and an asterisk (*) is postfixed to the downflooding point’s name in the Key Point Data table of the Results window.

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Emergence angles of the key points is also calculated – this is where they cross the waterline in an upward direction to become dry; as opposed to the immersion angle which is when the cross the waterline in a downward direction, becoming wet. A downflooding angle of zero degrees indicates that the key point is immersed at zero degrees of heel. Also see: Select View from Analysis Data on page 204. Water on Deck – Stockholm Agreementt Water on deck – Introduction

Water on Deck (WoD) requirements as described by the Stockholm Agreement may only be applied when doing Large Angle Stability analysis. During the development of this analysis capability, reference has been made to the following documents as well as direct correspondence with the MCA: Agreement Concerning Specific Stability Requirements for Ro-Ro Passenger Ships Undertaking Regular Scheduled International or Domestic Voyages between European Ports: MCA MSN 1790(M) –which supersedes MSN1673(M). http://www.mcga.gov.uk/c4mca/1790.pdf Guidance Notes On The Stockholm Agreement SLF 40/Inf.14 ANNEX 1 http://www.mcga.gov.uk/c4mca/con1_2a_ap3_1-2.pdf Water on deck – Technical Explanation

The effect of water on deck is calculated, in Maxsurf Stability, using the procedure outlined below: For a range of heel angles, the vessel is balanced to the loadcase displacement. Any damaged areas of the hull below the waterline are treated as lost buoyancy. These areas also include the areas where water on deck is specified but are below the waterline. The user may decide whether the vessel should be free-to-trim (i.e. the vessel is trimmed so that the rotated CG aligns longitudinally with the CB) or the vessel is held at a specified fixed trim and this longitudinal balance is not performed. At each heel angle, the vessel is balanced without the effect of water on deck (i.e. hull mass –as specified in the loadcase– is balanced against hull buoyancy and the longitudinal positions of the CG and CB are aligned if the user has selected a free-to-trim analysis). The minimum freeboard, within the specified damage extent, is then obtained with the vessel in this condition and used to determine the height of water on deck in the areas that the user has specified as accumulating water on deck. The mass and centre of gravity of the water on deck is computed. Note that no further balance of hull mass vs hull buoyancy or CG vs CB is performed at this point. The * modified vessel centre of gravity, CG , due to the additional mass of water on deck is then computed as follows:

CG * 

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CGWoD  M WoD  CG  M M WoD  M

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CGWoD is the centre of gravity of the accumulated water-on-deck; CG is the M centre of gravity of the vessel without water-on-deck; WoD is the mass of the where:

accumulated water-on-deck; and M is the mass of the vessel without water on deck. The modified righting arm is computed by adjusting the original righting arm (without water on deck) by an amount corresponding to the transverse shift of the centre of gravity:



GZ *  GZ  CG * y  CG y



and the metacentric height is modified by the vertical shift.



GM *  GM  CG * z  CGz



Given that y is positive to starboard and z is positive up and the vessel is heeling to starboard. The GM value is also modified to account for the transverse second moment of area of the WoD free-surface (using the vessel displacement, without including the mass of WoD). GZ is not modified because the actual centre of gravity of the WoD is calculated at each heel angle (similar to the "Simulate Fluid Movement" option for normal tanks).

Change in GZ due to water on deck

In Maxsurf Stability only the modified CG, GZ and GM due to the accumulated water on deck are computed. Neither the displacement nor any other hydrostatic parameters are modified nor is the vessel orientation (sinkage and trim) adjusted to take account of the water on deck. Water on deck – Using the Water on Deck analysis in Maxsurf Stability

The following section describes how to use the Water on Deck option in Maxsurf Stability. Specifying Water on Deck

Currently the water on deck (WoD) option may be applied only to the Large Angle stability analysis. The WoD option is an "Environment modifier" similar to the application of a Waveform. To turn on the WoD option. Select "Water on Deck" from the Analysis menu or toolbar:

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Water on Deck menu item in the Analysis menu and corresponding WoD dialog.

In the WoD dialog you can specify whether WoD should be applied and if so, the significant wave height. The significant wave height to be used depends on the sea-area in which the vessel is operating and is used (along with the freeboard) to compute the height of the WoD to be applied. Specifying areas where WoD is to be applied

Maxsurf Stability uses normal compartments (and tanks) to specify the areas of the vessel which are subject to water on deck. When the WoD option is turned on (see above) the display in the damage window will be modified. The longitudinal extents of damage are now displayed and instead of displaying check-boxes to select damaged areas, text is used to specify Intact, Damaged or WoD areas (only the first letter is required when modifying entries).

Enhanced Damage window when WoD analysis is selected

When entering the extents of damage in the table, the damage status of tanks is not modified. If the dialog is used (Case | Extent of Damage), all the extents may be specified and the damage status of tanks and compartments for the selected damage case will be updated depending on whether or not they are inside the rectangle defined by the damage extents. The fore and aft limits of the damage extent define the SOLAS damage length and it is the minimum freeboard in this range which is used to determine the height of the WoD. The extents of damage can be displayed by turning on the display of the Damage Zones. WoD areas are also treated as damaged and show in the colour of other damaged areas. The damage extent box is only shown when the vessel is at the DWL (i.e. not during analysis).

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Extents of damage (thick line) and damaged areas (red) Specifying freeboard calculation points

Due to the fairly complicated rules dictating the effective deck edge of WoD areas to be used for measuring the residual freeboard, Maxsurf Stability uses a new type of Key points to define the location at which the freeboard should be calculated. These are defined in the Key Points table:

WoD freeboard Key Points used to specify the freeboard deck height

The WoD freeboard key points are defined in the same way as other key points but should be linked to the compartments they define the deck for. You can define as many as required, depending on the hull curvature, but a minimum of two is recommended: one at the forward and one at the aft end of the compartment. As with other key points these are asymmetrical and it will be necessary to define key points on both sides of the vessel if the compartment is symmetrical. It is now possible to transversely snap Key points to the hull: simply specify the longitudinal and vertical coordinates, then select the rows of the key points you wish to snap and use the "Analysis | Snap margin line (or selected key points) to hull" command. If the margin line window is selected, then the whole margin line will snapped to the hull.

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When the analysis is started, Maxsurf Stability will automatically linearly interpolate extra points at the forward and aft extents of the damage and add these to the list of points used to find the minimum freeboard. The points used for determining the minimum freeboard are drawn in circles instead of crosses, see below:

Extra freeboard points are interpolated automatically a the ends of the extent of damage. The points used to determine the minimum freeboard are shown with circles instead of crosses. Water on deck information during analysis

During the analysis several additional items of information are displayed. First a dashed line shows the minimum freeboard. A second solid line of the same colour shows the height of WoD which has been applied. In addition, the centroid of the added mass of the water on deck and the lost buoyancy of any immersed damaged areas of each compartment are shown; the WoD centroid has "WoD" appended to the name of the compartment and the flooded volume has "LostB". The overall centre of gravity of the total WoD is show and labelled "WoD"; the modified centre of gravity of the vessel is also show, and is labelled "CG WoD"

Additional information shown in the drawing window Height of water on deck

The vertical position of the water on deck waterline is the greater of the “height of water on deck” added to: a) the waterline;

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b) the water on deck critical freeboard point (the lowest of the water on deck freeboard points)

hw measured from the waterline when freeboard points are immersed

hw measured from the lowest freeboard point when not immersed Water on deck results

With WoD applied, the GZ graph shows the modified GZ curve in addition to the normal GZ curve if desired (see Data | Data Format dialog)

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The WoD data may also be included in the GZ tabulated results:

Large Angle Stability results with new WoD results displayed. Stability criteria and Water on Deck

An additional check box has been added to the criteria dialog. This allows the user to specify that criteria should be evaluated and use the WoD-adjusted GZ curve. If WoD is select, damage will also be selected since WoD is only available for non-intact cases. Criteria that have the WoD option selected will only be evaluated if WoD is active and will use the WoD-adjusted GZ curve; if criteria should also be evaluated using the normal (unadjusted) GZ curve, copies of the criteria, without the WoD option selected, should be made.

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Water on Deck option for Stability Criteria; Criteria selected for WoD use the adjusted GZ curve Volume of Water on Deck

The volume of water on deck in the compartments selected for WoD, as well as any flooded volumes of these and damaged compartments, are given in the new "Compartments" table in the Results window; use the pull-down toolbar to select the heel angle to be viewed – see following section for more details.

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The volume of WoD and lost buoyancy is given in the Compartments table in the Results window

When rooms are made up of multiple linked sub-rooms, the first line shows the total for the complete room in brackets with the individual components listed below. This will be soon changed to show a completely separate row for the total room and below all the individual room components in grey.

Rooms with linked components

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Equilibrium Analysis

Equilibrium analysis lets you determine the draft, heel and trim of the hull as a result of the loads applied in the table in the Loadcase window. The analysis can be carried out in flat water or in a waveform. Choosing Equilibrium Analysis

Select Equilibrium from the Analysis Type option in the Analysis menu. Equilibrium Analysis Settings

 Displacement and Centre of Gravity using the Loadcase window

Also see: Setting the Frame of Reference on page 18 Equilibrium Analysis Environment Options

The following environments can be applied to the Equilibrium analysis:  Fluid simulation of tank fluid centre of gravity  Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar  Grounding (if any)  Criteria Equilibrium Results

Equilibrium Results are:  Hydrostatic data  Freeboard of key points, deck edge and margin line  Criteria evaluation  Wave phase animation  Curve of areas

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Hydrostatic data

Height/freeboard above free surface The freeboard of each Key Point is also calculated. The freeboard is for the vessel condition currently displayed in the Design view and is recalculated after each Equilibrium and Specified Conditions analysis. The freeboard calculated is the vertical distance of the Key Point above the local free surface; hence the local free surface height if a waveform is selected will be taken into account.

Freeboard of key points.

Negative freeboards, i.e. where the Key Points are immersed are displayed in red. The longitudinal positions at which the minimum freeboard for the margin line and deck edge occurred are also specified. Stability Criteria Evaluation The criteria results are displayed in the Criteria tab in the results window.

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Equilibrium Animation in Waves If performed in conjunction with analysis in waves, the Equilibrium analysis will automatically phase-step the waveform through a complete wavelength. This gives ten columns of results, one for each position of the wave crest. If necessary the results of this phase stepping can be animated giving a simple, quasi-static simulation of the hull motion in waves (Display | Animate). Note: This simulation only includes static behaviour at each wave phase, and does not cover dynamic or inertial forces. This can be done using Seakeeper. Equilibrium Concept

The definition of equilibrium is “Position or state where object will remain if undisturbed”. You can distinguish equilibrium into two types:  Stable, when disturbed the object will return to its equilibrium position  Unstable, when disturbed the object will not return to its equilibrium position

Stable equilibrium

Unstable equilibrium

With ships, an unstable equilibrium can exist when the KG > KM, i.e. the centre of gravity is above the metacentre (negative GMt). In real world a ship in unstable equilibrium will roll from the upright unstable equilibrium position to a position of stable equilibrium and assume an “angle of loll”. Since Maxsurf Stability starts the equilibrium analysis in upright position, it has no way of determining whether the equilibrium is stable or unstable. This means that unstable equilibrium may be found instead of the stable equilibrium. Therefore it is recommend to check the value of GMt yourself after doing an equilibrium analysis or perform a Large Angle Stability analysis and look at the slope of the GZ curve through the equilibrium heel angle.

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Unstable equilibrium

Stable equilibrium ”Angle of loll”

The graph above shows the results of a Large Angle Stability analysis for a vessel with negative initial GMt. In practice this vessel would have a loll angle of approximately 25 degrees. If an equilibrium analysis is performed for this vessel with the transverse arm set to zero, Maxsurf Stability will find the unstable equilibrium position with zero degrees of heel. In practice, it is desirable to find the stable equilibrium position. To do this, first ensure that the tolerances (Edit | Preferences) are set as sensitive as possible. This will ensure that the smallest possible heeling moment is required to find stable equilibrium position. Then create a very small heeling moment by offsetting one of the weight items in the loadcase window TCG by just a fraction. The equilibrium analysis will now find the stable equilibrium position. Note: It is good practice to always perform a Large Angle Stability analysis as well as the equilibrium analysis to check if the vessel is in stable or unstable equilibrium. This is most likely to occur if the VCG is too high and the vessel has negative GM when upright. The problem can be overcome by offsetting the weight of the vessel transversely by a small amount. Specified Conditions

Specified Condition analysis lets you determine the hydrostatic parameters of the vessel by specifying the heel, trim and immersion. Heel can be specified by either the angle of heel or the TCG and VCG. Trim can be specified by the actual trim measurement, or the LCG and VCG. Immersion can be specified by either the displacement or the draft. Choosing Specified Conditions

Select Specified Conditions from the Analysis Type option in the Analysis menu or toolbar.

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Specified Conditions Settings

The settings required for Specified Condition analysis are:  Specified Conditions from the Analysis menu

Three Sets of variables are provided, labelled Heel, Trim and Immersion. One choice must be made from each of these groups. Maxsurf Stability will then solve for the vessel hydrostatics at the conditions specified.

Values from the current loading condition can be inserted into the Centre of Gravity and Displacement fields by clicking on the Get Loadcase Values button. Also see: Setting the Frame of Reference on page 18 Specified Conditions on page 190 in the Analysis Settings section. Note: If the fluid simulation has been turned on in a previous analysis mode, then the VCG obtained from the loadcase will not include the free surface correction; the “Get Loadcase Values” button will return exactly the displacement and CG as displayed in the current loadcase window. The specified condition analysis itself ignores tank fillings and does no correction to VCG. Specified Conditions Environment Options

The following environments can be applied to the Specified Condition analysis:  Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar

Specified Conditions Results

The specified conditions results are the same as equilibrium analysis results except that criteria are not evaluated, i.e. hydrostatic data and key points freeboard are calculated.

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KN Values Analysis

KN Values Analysis allows you to determine the hydrostatic properties of the hull at a range of heel angles and displacements to produce the cross curves of stability diagram. Choosing KN Values Analysis

Select KN Values from the Analysis Type option in the Analysis menu or toolbar. KN Values Analysis Settings

The analysis settings required for KN Values analysis are:  Heel from the Analysis menu, select range for analysis  Trim (fixed or free) from the Analysis menu  Displacement from the Analysis menu, select range for analysis and specify estimate of VCG if known

The heel angles used may differ from those used in the Large Angle Stability and Limiting KG analyses. To set the range of angles, select Heel from the Analysis menu. A range of displacements for KN calculations can be specified using the Displacement command from the Analysis menu. Initial and final displacements can be entered, together with the number of displacements required.

Displacement range dialog

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Trim dialog

The VCG can also be entered (specified from the vertical zero datum). Traditionally, KN calculations are calculated assuming the VCG at the baseline (K). However if the analysis is being calculated free-to-trim and an estimate of the VCG is known, the accuracy of the KN calculations (for VCGs in the vicinity of the estimated VCG) may be improved by calculating the GZ curve using the estimated VCG position – this will reduce the error in the trim balance due to the vertical separation of CG and CB because this vertical separation is specified more accurately than simply assuming the VCG at the baseline. If a VCG estimate is specified, the KN values are still presented in the normal manner with the KN values calculated as follows: KN(φ) = GZ(φ) + KG_estimated sin(φ) For information on Trim settings for KN Analysis, see: Trim on page 187 Also see KN Value Concepts on page 122 KN Values Analysis Environment Options

 Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar

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KN Values Analysis Results

KN curves calualated at each heel angle

Immersion angles calculated at each displacement KN Value Concepts

The righting lever, GZ, may be calculated from the KN cross curves of stability (at the desired displacement) for any specified KG using the following equation: . GZ = KN - KG sin(φ)

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M

Z G

B’ B

N

K

Note: KN values can also be referred to as “Cross curves of stability”. Limiting KG

Limiting KG analysis allows you to analyse the hull at a range of displacements to determine the highest value of KG that satisfies the selected stability criteria. GZ curves are calculated for various KG values. After each cycle, the selected criteria are evaluated to determine whether the CG may be raised or must be lowered. When comparing the results of a limiting KG analysis to that of a Large Angle Stability analysis, it is essential that the same heel angle intervals are used and that the free-totrim options and CG are the same. Some criteria, notably angle of maximum GZ, are extremely sensitive to the heel angle intervals that have been chosen. Choosing Limiting KG

Select Limiting KG from the Analysis Type option in the Analysis menu or toolbar. Limiting KG Settings

The initial conditions required for Limiting KG analysis are:  Displacement from the Analysis menu, select range for analysis  Heel from the Analysis menu, select range for calculation of GZ curves  Trim (fixed or free) from the Analysis menu

The range of displacements to be used is set in the same way as they are set in the KN analysis. The heel angles used may differ from those used in the Large Angle Stability and KN analyses. To set the range of angles, select Heel from the Analysis menu. See Large Angle Stability on page 100 for further details. For information on Trim settings for Limiting KG Analysis, see: Trim on page 187

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Note: Since Limiting KG can be quite a time consuming analysis, you may wish to use a smaller number of heel angles than for the Large Angle Stability calculations. (However this will cause some loss of accuracy.) Limiting KG calculations will be significantly faster if the trim is fixed. Limiting KG Environment Options

 Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar  Criteria

Limiting KG Results

Limiting KG analysis results are  Limiting KG values, for each displacement and the limiting criterion.  Limiting KG vs displacement graph

The Limiting KG value is measured from the baseline, which is not necessarily the same as the zero point. As well as the limiting KG, the minimum GM, draft amidships, trim and centre of gravity are given in the results table. The Limiting KG analysis also checks that any selected equilibrium based criteria are passed at each VCG that it tries. However, you must still have at least one Large Angle Stability criterion selected. Criteria are only evaluated on the positive side of the GZ curve, so if there is any form of asymmetry, it may be necessary to run the analysis heeling the vessel to both starboard and port (this can be done automatically in the Batch Analysis).

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After a Limiting KG analysis has completed, the results in the Criteria results table display “Not Analysed”, this is because they do not necessarily refer to the final KG and would be misleading. If you require the limiting KG for each criterion individually or wish to perform a Large Angle Stability and Equilibrium analysis at each of the displacements and the corresponding limiting KG, this can be done in the Batch Analysis. Some criteria may depend on the vessel displacement and or vessel’s VCG. Where these values are explicit in the criterion’s definition in Maxsurf Stability, the correct values of displacement and VCG will be used in the evaluation of these criteria. However, problems can arise if the criterion is only available in its generic form – most commonly heeling arm criteria where the heeling arm is specified simply as a lever and not as a moment. In this case, since the heeling arm is not related to the vessel displacement in its definition within Maxsurf Stability, the heeling arm will remain constant for all displacements (where it is perhaps desired that the heeling arm should vary with displacement. For example in the case where the heeling moment, rather than the heeling arm is constant). Important: For important information on varying displacement while evaluating criteria see Important note: heeling arm criteria dependent on displacement on page 290. Also see: Convergence Error on page 191 in the Analysis Settings section.

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Limiting KG Concepts

Maxsurf Stability will iterate to a KG value that just passes all criteria you have specified in the criteria dialog. Maxsurf Stability will start with a set start KG value (e.g. 1 meter), run a large angle stability analysis and check the selected criteria. If any of the criteria fail, Maxsurf Stability will lower the KG and try again. If the criteria pass, Maxsurf Stability will raise the KG value and try to make the criteria fail. Maxsurf Stability will continue doing this until the limiting KG value has been iterated to within 0.1mm. If this tolerance is not achieved in a certain number of iterations, Maxsurf Stability will move on to the next displacement. When performing a Limiting KG analysis, Maxsurf Stability will evaluate any equilibrium-based criteria that are selected for testing and act accordingly. However, at least one GZ-based criterion must also be selected. This is because to perform a sensible search, Maxsurf Stability must have at least one criterion that will improve by reducing the VCG; Maxsurf Stability assumes that raising the VCG will make criteria more likely to fail and that reducing the VCG will make the criteria more likely to pass. This is not necessarily the case for equilibrium-based criteria such as freeboard requirements or for GZ-based criteria such as Angle of maximum GZ; if only these types of criteria are selected, Maxsurf Stability may have difficulty in finding a true limiting KG and specify convergence errors. Limiting KG for damage conditions with initially loaded tanks

The set up of the Limiting KG analysis parameters has been modified to facilitate setting up the required TCG when calculating the Limiting KG for a damaged vessel where liquid cargo tanks initially carrying cargo or ballast water are damaged. Maxsurf Stability assumes that damaged tanks lose all liquid cargo or ballast that they may have been carrying and their buoyancy is lost from the vessel – analysis is done by the lost buoyancy method rather than the added mass method. For Limiting KG calculations for a damaged vessel where some of the damaged tanks were initially non-empty, it is often required to specify a required TCG. This is because under most circumstances, the intact vessel is upright (zero heel). The tanks would generally provide a transverse moment that must be balanced by the mass of the vessel, which must therefore be offset. Note that we are only concerned about the tanks that will be damaged and that initially contain cargo or ballast; this is because when they are damaged the ballast or cargo is assumed to be totally lost from the vessel. (Although seawater enters these damaged areas, this is not seen as an additional mass because damage is computed by the lost buoyancy method.) Two methods of specifying the required TCG are possible. The second method was available in older versions of Maxsurf Stability and it is the first method that provides the additional functionality: 1. Current loadcase specifies initial loading of damaged tanks: This means that the currently selected Loadcase will be used to define the volume of cargo or ballast in tanks before damage is applied. If this method is selected Maxsurf Stability will look at the mass and CG of cargo or ballast in tanks which will be damaged during the analysis. This is used to compute required TCG. Note that all results and input data will be assumed to be for the intact vessel. That is the specified displacement will be that of the intact vessel and that the resulting LCG, TCG and KG will also be for the intact vessel. If the vessel has an off-centre intact TCG, this can be specified below (if the vessel is symmetrical and initially upright, this should be zero). Page 126

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2. The second option is for the used to specify the required TCG directly. This functionality has been in Maxsurf Stability for many years. In this case, however the specified displacement and CG corresponds to that of the intact vessel with damaged tanks empty. i.e. the mass and CG of the intact vessel after deducting the masses of cargo or ballast in any tanks that will be damaged. Example calculations

It is probably simplest to explain this functionality by means of an example. The following sample calculations demonstrate how the new Limiting KG options may be used. A vessel with a port-side tank that are initially full will have this tank damaged. We wish to find the maximum VCG that the intact vessel may have in order to pass the selected stability criteria. Initial tank loadings

First we need to define how much cargo is in the tanks that will be damaged. This is done by defining a loadcase and switching to the intact mode to specify the tank filling levels. Here we have specified that the tank is 80% full before the damage is applied.

Use a loadcase to specify the initial quantities of fluids in tanks Setting the Displacements

Secondly we need to define the displacement range we wish to calculate the Limiting KG for. This is done in the Displacements dialog:

Displacement dialog Setting the Trim options

We now need to specify the trim options we wish to use. In this case we shall use free to trim, but with an initial vessel trim of 0.25m by the stern. Importantly we shall also specify that the current loadcase should be used to determine the required TCG and because the vessel is symmetrical, the specified TCG is zero:

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Trim and TCG specification Running the Analysis

We now need to select the damage case to be evaluated, the stability criteria that need to be passed and a suitable range of heel angles to be computed to evaluate the criteria. We also need to determine which way we should heel the vessel and in doubt should try heeling the vessel in both directions to see which will give the worst result. In this case large port-side tanks are to be damaged; these are filled significantly above the waterline so loss of ballast from these tanks will cause a list to Starboard, so the analysis should be done in this direction. Results from Limiting KG analysis

Limiting KG results Validation of results

The results can be validated by completing a Large Angle Stability analysis with the specified displacement and CG. It must be remembered that these are KG results not VCG so when checking the VCG must be calculated. In this case the baseline (K) is at – 356.845mm

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Model baseline

Computed VCG values

We can now set up a loadcase for one of the displacements. Remember that these are the intact vessel displacement and CG:

Loadcase to check calculated Limiting KG

When the analysis is run, it can be seen that (as expected) the stability criterion is passed with a very small margin.

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Criterion is passed with a small margin

Floodable Length

The Floodable Length analysis allows you to calculate the longitudinal distribution of maximum length of compartments that can be flooded with the vessel still passing specified equilibrium criteria. The results are presented as the maximum length of compartment plotted (or tabulated) against the longitudinal position of the compartment’s centre. Traditionally the criterion of margin line immersion is used to compute the Floodable Length curve. The Floodable Length may be computed for a range of displacements and compartment permeabilities. Choosing Floodable Length 

Select Floodable Length from the Analysis Type option in the Analysis menu or toolbar.

Floodable Length Analysis Settings

The initial conditions required for Floodable Length analysis are:  Trim (free-to-trim, either initial trim or specified LCG)  Displacement, select range and specify VCG  Permeability, select range  Bulkhead location (if applicable)

1. The analysis is always carried out free-to-trim, but the centre of gravity can either be specified directly in the Trim dialog or it is computed from the specified initial trim. For information on Trim settings for Floodable Length Analysis, see: Trim on page 187. The range of displacements to be used is set in the same way as they are set in the KN and Limiting KG analyses. The VCG must also be specified since the Floodable length analysis is very sensitive to accurate trim calculations. This means that the vertical separation of CG and CB is accounted for in the trim balance. The permeability dialog is used to specify the permeabilities to be used for the Floodable Length analysis; the permeability is applied over the entire length of the vessel and is also applied to the free-surface when calculating the reduction of waterplane area and inertia.

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This permeability is unrelated to the permeability when defining compartments and is only used for floodable length calculations. Floodable Length Environment Options

 Density  Wave Form (if any)  Damage: no damage case may be selected as this is automatically defined by the analysis. The Intact condition is automatically selected and the Damage toolbar is disabled

 Criteria from the Analysis menu, select which criteria should be evaluated

Criteria must be specified from the analysis menu. These are used to compute the Floodable Lengths.

Note that internally, Maxsurf Stability will treat the vessel sinking or the trim exceeding +/-89º as a criterion failure. Floodable Length results

The results of the analysis are given in tabulated format at the stations defined in the Maxsurf Design Grid as well as graphical format. The tabulated data is linearly interpolated from the graphical data. (The raw graph data can be accessed by double clicking the graph.) There are several graph plot options available in the Data | Data format dialog (when the floodable length graph is topmost). The vessel profile (centreline buttock) may also be displayed. All compartment standards up to the maximum specified will be plotted.

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Floodable lengths graph options:  Fix the y-axis so that it is the same scale as the x-axis.  Plot the different compartment standards up to a specified maximum value.  Vessel profile (shown in light grey)  Floodable Length Bulkheads locations are specified in a table in the Input window. The graph updates in real time as you adjust the bulkhead locations so once you have calculated the floodable lengths, you can quickly adjust the bulkhead locations so that the vessel meets the required compartment standard.

If the analysis is unable to find a condition where the vessel passes the selected criteria, the following dialog will be displayed. The vessel sinking or the criteria failing in the intact condition could cause this.

Floodable Length Concepts

The analysis is performed by defining a flooded compartment, with the centre of the compartment at a section under investigation. The length of this flooded compartment is increased section-by-section until one of the criteria is failed. The compartment is then moved progressively forward along the vessel. This process may be visualised by turning on the display of the Maxsurf Stability sections.

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Note: Speed versus Accuracy The analysis will be both considerably more accurate and slower with a larger number of sections in the Maxsurf Stability model; it is recommended that a minimum of 100 sections be used for most situations. The speed of the analysis can be increased quite considerably by increasing the allowable tolerances in the Edit | Preferences dialog. Longitudinal Strength

Longitudinal Strength lets you determine the bending moments and shear forces created in the hull due to the loads applied in the Loadcase window. The analysis can be carried out in flat water or in a specified waveform. Choosing Longitudinal Strength

Select Longitudinal Strength from the Analysis Type option in the Analysis menu or toolbar. Longitudinal Strength Settings

The initial conditions required for Longitudinal Strength analysis are:  Displacement and Centre of Gravity using the Loadcase window  Distributed loads using the Loadcase window

When the Longitudinal Strength analysis mode is selected, two extra columns appear in the Loadcase window. These are used to specify the longitudinal extents of the load. A trapezium shaped distributed load is derived from the centre and fore and aft extents of the load. See the Loadcase Longitudinally Distributed Loads section on page 50 for more details. Longitudinal Strength Environment Options

 Density  Wave Form (if any)  Damage (or Intact) from the Analysis toolbar  Grounding (if any)  Criteria, allowable shears and moments from Input window

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Note that Maxsurf Stability will always use the fluid simulation method when performing a longitudinal strength analysis. For more information on how Maxsurf Stability can take fluids in tanks into account see Fluids Analysis Methods on page 193. Longitudinal Strength Results

The output from the longitudinal strength calculations is a graph of mass, buoyancy, damage and non-buoyant volumes and grounding loads. From these, the net load, shear force and bending moment along the length of the hull are computed. If defined, allowable shear forces and bending moments are overlayed on the graph. Downward acting masses, such as normal masses in the loadcase or lost buoyancy due to damage, are given positive values. Upward acting forces such as buoyancy and grounding reactions are given negative values.

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Name of Curve Mass Buoyancy

Grounding Damage/NBV Net Load Shear

Description Vessel mass / unit length Buoyancy distribution / unit length = immersed cross sectional area * density. Damaged tanks and compartments reduce the buoyancy. Grounding reaction Loas buoyancy due to damaged tanks and compartments and Non-Byoyant Volumes (NBV) Mass + Buoyancy + Grounding + Damage (and NBV) x

Shear Force =

 NetLoad( x)dx AftSt

Moment

x

Bending Moment = 

 ShearForce ( x)dx AftSt

Allowable shear and moment

Allowable shear and bending moments as specified in the input Modulus table.

This data is also displayed in the “Long. Strength” tab in the Results window. You can display this table by choosing Longitudinal Strength from the Results sub-menu under the Window menu; alternatively double-clicking in the graph will give you all the data as plotted. Note Make sure you have defined sections in your model in Maxsurf. Without this, the longitudinal strength table will be empty.

Note: For the purposes of strength calculations, any point loads in the loadcase will be applied as a load evenly distributed 100mm either side of the position of the load. Tanks are taken into account as distributed loads as well based on their mass distribution that is calculated from the tank sections.

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Tank Calibrations

Tank Calibration allows you to determine the properties of the tanks you have defined in the Compartment window, at a range of capacities. Choosing Tank Calibrations

Select Tank Calibrations from the Analysis Type option in the Analysis menu or toolbar. Tank Calibration Input

 Tank definitions and boundaries  Permeability  Fluid type

The above data are specified in the Compartment and Sounding Pipes definition tables. Also see: Relative Density of Tank Fluids on page 67 Tank Calibration Settings

 Trim range, angle or trim measurement  Heel angle range  Which items to be calibrated: Analysis | Calibration options dialog

Analysis | Calibration options dialog: Compartments and Non-buoyant volumes may be calibrated if desired Tank Calibration Environment Options

 Calibration intervals – see Sounding Pipes Tank Calibration Results

If a range of heel (and / or trim) angles have been defined, you may select which are displayed in the results table and graph using the Results toolbar. If Compartments or Non-buoyant volumes have also been calibrated, they are shown in grey.

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You may chose which columns are displayed using the Data Format dialog:

In the Window | Graphs menu each tank can be selected for display in the Graph window. For more information see Chapter 5 Maxsurf Stability Reference.

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Tank calibration calculations

A number of data are calculated for the tanks. These include the tank inertias about their centre of gravity, the wetted surface area of the tank and the free-surface area. The wetted surface area of the tank includes only that part of the tank that is wet by the fluid in it at the corresponding sounding level, the top of the tank is only included when the tank is pressed-full. The inertias are in fact “volume inertias” in that they are not multiplied by the density of the fluid in the tank. The following notation is used: x longitudinal-axis y transverse-axis z vertical axis

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Calculation of tank inertias, where M and dm indicate an integration over the volume of fluid in the tank. Sounding pipes and tank calibration results

If the vessel is trimmed, there are ranges of tank volumes that will show the same sounding/ullage. (The same effect can occur if the sounding pipe does not reach the lowest or highest point in the tank – remember that this can change as the vessel trims, which is effectively what is happening in the figures below). These points occur when the tank is near empty or near full, see below (increasing the trim, will exacerbate this phenomenon):

Figure a Zero trim

Figure b Trim by bow, nearempty tank

Figure c Trim by bow, near-full tank

Figure a shows a sounding pipe that extends the whole height of the tank, with the vessel at zero trim. Here all tank filling levels will have a valid sounding. Figure b shows the vessel with (bow down) trim and a small amount of fluid in the tank. Here there will be a range of tank filling levels which all show zero sounding. Figure c shows the vessel with the same trim, but with the tank nearly full. Here there will be a range of tank filling levels that all show maximum sounding.

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These effects will be noted in the tank calibration results if they are extreme enough since Maxsurf Stability always adds calibrations at 1%, 97.9%, 98% and 100% full; if the 1% level does not intersect the sounding pipe, the sounding will be given as zero. Similarly if the 97.9%, 98% and 100% full levels do not intersect the sounding pipe, the maximum sounding will be displayed, see below. In the results out lined in red, there are four results which all have a sounding of 1.0m but different capacities – the fluid levels are all above the top of the sounding pipe. In the blue results, the last two results are below the bottom of the sounding pipe, giving soundings of 0.0m but different capacities (the last but one calibration point is the fluid remaining in the tank when the sounding is 0.0m).

Tank calibrations for severely trimmed vessels; sounding pipe does not cover full range of tank capacities. The profile view of the tank in the trimmed vessel is shown on the right; the sounding pipe is in the middle of the tank and extends from the bottom to the top of the tank.

In a similar way, if the sounding pipe extends above or below the maximum and minimum fluid levels, you will get readings which have the same capacity but different soundings. Sounding intervals

The sounding intervals for the calibration table may be:  Automatic,  User defined  Fredyn – {0%, 0.1%, 5%, 10%, … , 85%, 90%, 95%, 99.9%, 100%}  Max. only – {100%}

In automatic mode the increments along the sounding pipe are chosen depending on the height of the tank to give approximately 20 soundings. Alternatively you may specify a precise sounding step (this is the step along the sounding pipe, not the vertical step of the tank level). Finally a “Fredyn” sounding list may be generated, this gives intervals of {0%, 0.1%, 5%, 10%, … , 85%, 90%, 95%, 99.9%, 100%} of the full capacity of the tank. To specify the interval, type “A”, “F”, “Max” or a numerical value in the “Calibration Spacing” column of the Sounding Pipe definition table.

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Note: Backward compatibility with earlier versions of Maxsurf Stability If the model is saved with Fredyn calibration intervals and is loaded into an earlier version of Maxsurf Stability, you must change the calibration intervals to Automatic or a positive value otherwise Maxsurf Stability will crash during the tank calibration analysis. Fredyn calibration intervals

The tank calibrations normally follow regular length intervals along the sounding pipe. A common sounding pipe is used for “Fredyn tanks”, this sounding pipe starts at the vessel zero point and projects vertically upwards; all soundings for “Fredyn tanks” use this common sounding pipe.

Fredyn sounding pipe

The tank calibration intervals required by Fredyn are (as a percentage of full capacity) {0.1, 5.0, 10.0, …, 90.0, 95.0, 99.9}. To use these intervals, type “Fredyn” in the Calibration Spacing column of the Sounding Pipes Definition table:

Specification of Fredyn calibration intervals

Note that Compartments and non-buoyant volumes are always calibrated at the calibration intervals required by Fredyn. If only the 100% full values are required “Max” may be specified for the calibratin spacing. MARPOL Oil Outflow

MARPOL probabilistic oil outflow calculation may be computed according to the following MARPOL regulations: Resolution MEPC.141(54), Regulation 12A: Oil fuel tank protection Resolution MEPC.117(52), Regulation 23: Accidental oil outflow performance Define the tanks in the Compartment definition window then choose the MARPOL analysis mode. Seltect the Reolution and tanks to be included in the analysis in the MARPOL options (Analysis menu) dialog (see below). MARPOL Options dialog (Analysis menu)

The MARPOL options dialog allows the user to select the tanks that should be included in the analysis for both MARPOL Regulations.

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Tank selection for the MARPOL analysis

The list of selected tanks is different for both Regulations since Regulation 12A is for fuel tanks and Regulation 23 applies to cargo tanks. Further each tank has the option for being included in the computation for outflow due to side- and bottom-damage. When you select a Regulation with the radio buttons, the corresponding list of selected tanks will be displayed in the grid. MARPOL Tank measurements

If the “Update all tank measurements” check-box is ticked, then Maxsurf Stability will attempt to measure the required tank parameters (over-writing any that have previously been manually edited). Due to the nature of some of the measurements, it is not possible to guarantee that Maxsurf Stability will be 100% accurate in interpreting the measurements as defined in the MARPOL documents, for this reason the user should carefully review the values generated by Maxsurf Stability. MARPOL Results and additional Input

Because the calculations of the MARPOL analysis are very quick they are done in realtime as input data is edited by the user. For this reason the data input and results are combined in one table. The table is in the MARPOL tab of the Results window:

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MARPOL calculations: Results Window

The table is split into three parts: main Hull parameters, oil outflow due to Side damage and finally oil outflow due to Bottom damage. Parameters that can be edited are shown in black; those which cannot are shown in grey. Main Hull Parameters

Different parameters are shown depending on the Regulation being used. Regulation 23 calculates the nominal oil density as the deadweight divided by the total tank capacity; the deadweight is computed as the difference in displacements between the deepest loadline draft and the lightship draft (or may be specified directly). For Regulation 12A, the nominal fuel oil density is specified by the user, the default being 1000kg/m3. Furthermore the inert gas overpressure may be specified for Regulation 23. The deepest loadline draft is taken as the DWL draft; the lightship draft is used to calculate the deadweight for Regulation 23 and the partial draft, which affects bottomdamage outflow in Regulation 12A. If a parameter is modified, it is possible to revert back to the Maxsurf Stability calculated value or default by typing ‘H’ or double clicking:

Reverting back to default/calculated parameter values

For full definitions of the parameters, please refer to the relevant IMO instruments.

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Main hull parameters required for each Regulation Tank Parameters

Calculations are shown further down; listing first side-damage tanks, then bottomdamage tanks. The user-editable tank parameters are the main dimensions which affect the probability of damage. These should be carefully checked since these can be difficult for Maxsurf Stability to automatically measure in some cases. For tanks which are to be considered for both side- and bottom- damage, these values are linked so it is only necessary to edit them in one location. Note: Maxsurf Stability will overwrite user-edited tank parameters! Remember that any data that you change manually will be overwritten by Maxsurf Stability if the “Update all tank measurements” option is ticked in the MARPOL options dialog. It is advisable to copy any manually edited data to a spreadsheet or text file if you only want to update the measurements of some tanks.

For full definitions of the parameters, please refer to the relevant IMO instruments Small tanks

MARPOL RESOLUTION MEPC.141(54), Regulation 12A – Oil fuel tank protection allows for the contribution of small tanks to be excluded provided the total capacity of these small tanks is less than 600m3; small tanks are defined in 3.12.

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It is now possible to exclude these tanks in Maxsurf Stability by specifying the maximum volume of “small tanks”.

Maxsurf Stability uses the geometric volume multiplied by the MARPOL permeability of 99% to calculate the “maximum capacity” of the tank. Any tanks which are above this limit do not provide a contribution to the calculated outflow parameter. The show “Small tank” in the OS.P(S) column along with their “maximum capacity” (note that the loading volume is taken at 98% full).

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There is no automatic check for the aggregate capacity of these excluded “small tanks”. However if it exceeds the 600m3 limit, the user can reduce the capacity that defines “small tanks” to bring it under this limit.

Saving

With the MARPOL sheet active, the MARPOL data may be saved; it is also saved in the main .hmd file when the design is saved. Probabilistic Damage IMO Probabilistic damage

Maxsurf Stability support for Probabilistic damage according to both IMO MSC.216(82) and IMO MSC.19(58) . MSC.216(82) can be applied to both dry cargo and passenger ships whilst MSC.19(58) is applicable to dry cargo vessels only. Definitions

It is useful to clarify some of the terminology used in the Maxsurf Stability documentation: The following definitions have been taken from MSC.216(82) and MSC.281(85):

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Room

Watertight space -- this would be a Maxsurf Stability Compartment or Tank. Note that in Maxsurf Stability a complex tank geometry can be defined by a parent and a number of Linked Tanks -- these Linked Tanks are considered to be joined allowing free movement of water from one part to another (there is no requirement in Maxsurf Stability that the individual linked parts be physically adjacent. Thu a tank made up of multiple linked parts is considered that all parts flood (or fill) together and share a common waterline. It should also be noted that the individual parts making up a Linked tank may have different permeabilities (this differs slightly from the IMO definition above). Space

We use the same definition as IMO “a combination of rooms”. Under most circumstances, this would be a contiguous group of rooms (i.e. spatially adjacent to one another -- though given that Maxsurf Stability linked tanks are not necessarily adjacent, this spatial adjacency is not enforced.) Damage

Again we use the same definition as IMO “3D extent of breach of the ship” but in the Maxsurf Stability context the extent is always cuboid: defined by planar fwd, aft, port, stbd, top and bottom limits. This may be a full longitudinal zone or may be limited in transverse and/or vertical extent by longitudinal bulkheads and/or decks; there may also be multiple adjacent zones damaged. Damage Space

We use this definition in Maxsurf Stability to specify which rooms will be breached when a given damage occurs. Damage Case

A specific instance of flooded compartments for which the vessel GZ curve is to be calculated. During the Probabilistic damage analysis in Maxsurf Stability, Damage cases are assembled from the definition of the Damage Spaces for different combinations of damage.

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Essentially the probabilistic damage analysis performs a number of large angle stability analyses and uses the IMO criterion to determine an s-factor that depends on certain parameters of the GZ curve. The GZ curves are calculated for a large number of different damage conditions and several load cases. For each condition, a p-factor can be calculated. The vessel’s attained subdivision index is the sum of the products of the pfactors with their corresponding s-factors. The attained subdivision index can then be compared with a required subdivision index to see if the vessel achieves a sufficiently high degree of safety. Flow through – Typical Use-case

The following section shows how the probabilistic damage analysis might typically be used.  Maxsurf model is loaded as normal  User defines (first selecting File | New to open the Probabilistic damage data table) other ship data required for the probabilistic damage analysis in the Damage window | Global table.

 User defines the damage zones they wish to consider in the Damage window | Zones table

 Once 2 and 3 have been completed, the p-factors Damage window | p Factors table are automatically calculated and displayed as the zone data is modified. It is useful to have this interaction because if the p Factor is too large for a particular zone, the user may decide to refine the zone arrangement.

 User defines the bulkheads and deck values for single and groups of adjacent zones.

 When the Zones have been defined the user can then define which tanks are damaged in each zone in the Damage window | Zone damage table. A first pass at this can be automatically generated using the Case | Extent of damage command.

 The user can then perform the probabilistic damage analysis. Maxsurf Stability runs a large angle stability analysis for each combination of loadcase and damage and collates the results to calculate the attained index. This is then compared with the required index.

During the analysis each GZ curve and details on the evaluation of the s-factor may be saved in a log file. The same log file is used for each analysis so it is important to either change the name or copy the file at the end of the analysis if the results are to be kept. The log file parameters may be specified in the Edit | Preferences dialog:

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Probabilistic damage result logging options (Edit | Preferences) Finding the probabilistic damage input sheets.

The probabilistic damage input sheets are in the damage window after the normal damage condition sheet.

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A Probabilistic Damage toolbar button is available in the Windows toolbar which will take the user back to the last used probabilistic damage input table:

Probabilistic damage – Saving input parameters

The probabilistic damage data is saved in the .hmd file. However this is new to version 14.1 and if the file were read into an earlier version of Maxsurf Stability and saved, these data would be lost. For this reason it is also possible to save the probabilistic damage data as a separate file (in a similar way to the other Maxsurf Stability input data). To load or save the probabilistic damage data as a separate file, ensure that one of the probabilistic damage data sheets in the Damage window is on top.

Bring one of the probabilistic damage tables to the front to enable File menu items Probabilistic damage – Inputs

In this section we shall look at the input parameters required for the probabilistic damage analysis. Settings for Probabilistic damage GZ curve calculation

Since the analysis essentially consists of a large number of GZ curve calculations, most of the settings that are applicable to the Large Angle Stability analysis are also applicable to the Probabilistic Damage Analysis. Chose the Probabilistic Damage analysis mode from the pull-down or Analysis menu:

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Selecting Probabilistic Damage anlysis mode

Once you have selected the probabilistic damage analysis mode, you can define the heel angle range and trim settings to be used as well as any environmental parameters such as waveform (as well as the fluid analysis method to be used). During probabilistic damage analysis, it is possible to check the vessel heeling to both port and starboard. This is useful if the tanks contain ballast or cargo and it is uncertain in which direction the vessel will list when damaged (or indeed the vessel may list to different directions depending on the loadcase and damage). Maxsurf Stability will calculate the GZ curve in both directions and, if the criteria can be evaluated in both directions, the lowest s-factor will be taken. If the criteria can only be evaluated in one direction, then this value for the s-factor will be taken. It is recommended to evaluate at least one negative heel angle and the direction of heel should correspond to the side of the vessel that is being damaged (see below):

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Heel angle specification (as per Large Angle Stability)

Use either fixed trim or free to trim to loadcase. s-factor calculation

The s-factors are calculated by stability criteria. The Probailistic damage analysis has its own set of criteria (though the same parent criteria are also available in the large angle stability analysis criteria). When the analysis mode has been set to Proababilistic Damage, you will see the criteria that are used for this analysis. The number of parent criteria is reduced to only those which can calculate the s-factor. Also some “Default” criteria are supplied, you can add or modify these should you so desire. When running the analysis, Maxsurf Stability will look at the probabilistic criteria that have been selected and warn you if there are any problems.

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Probabilistic Damage Criteria Manager with Parent and Default criteria

The following rules should be observed when defining the probabilistic damage criteria:  As with the normal criteria manager, changes made to the parent (bold) criteria are not saved. If you need to modify any of the criteria you should make your own copies of the parent criteria

 A set of Default criteria are provided – these can be modified and changes will be saved.

 Only one criterion should be selected and it should correspond to the IMO Resolution being used. (Strictly, you may have up to one of each MSC.216(82) or MSC.19(58) criteria selected and Maxsurf Stability will automatically use the appropriate one – according to the selected Resolution in the Global sheet – but for clarity, it is probably best practive to just have a single criterion selected.)

 The criteria should always be selected for Damage analysis.  Maxsurf Stability will automatically update some of the criteria parameters according to corresponding parameters in the probabilistic damage setup. However it is still good practice to review criteria parameters before starting the analysis. This is particularly true for the MSC.216(82) Resolution where the vessel type and heeling moments must be defined correctly.

 The criteria window can be closed with either of the close buttons.

For further information on how the s-factors are calculated and the different parameters, please refer to the Criteria Help section for the appropriate criteria (and heeling arms). Main parameters and calculation of required subdivision index

The other parameters required for the probabilistic damage analysis are defined in the last four tables in the Damage window:

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Additional tables in the Damage window define the remaining Probabilistic damage input data

Depending on the selected IMO Resolution, different rows and columns will be displayed in the tables; both MSC.216(82) and MSC.19(58) are provided, A.265 VIII is not included. Tool tips have been added to provide a more detailed explanation of the input parameters and also the options available.

Tool tips for Global data sheet Global table

This table is used to define the main parameters for the probabilistic damage anlysis as well as provide some intermediate calculations. Input data are shown in black whilst results are shown in grey. Depending on the Resolution and vessel type, some rows may be hidden.

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Global table – MSC.216(82) Dry Cargo vessel and Passenger vessel

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Global table – MSC.19(58) Dry Cargo

Row Resolution -MSC.216(82) or MSC.19(58) Deepest subdivision draft (summer loadline) Loadcase Partial subdivision draft Loadcase Light service draft Loadcase Type -- Cargo or Passenger Lifeboat capacity N_1 Permitted max. num. of persons in excess of N_1: N_2 max. moulded breadth at or below deepest subdivision draft: B max. number of adjacent zones to consider min. p-Factor of damage to consider Page 156

Description IMO Resolution to be used.

Name of loadcase that defines the vessel at the deepest subdivision draft. Name of loadcase that defines the vessel at the partial subdivision draft. Name of loadcase that defines the vessel at the light subdivision draft. not required for MSC.19(58). Vessle type. not required for MSC.19(58). Number of persons for whom lifeboats are provided. required for MSC.216(82), pax. Vessel only. Number of persons inclusing officers and crew that the vessel is permitted to carry in excess of N_1. required for MSC.216(82), pax. Vessel only. Parameter not currently used.

Specifies the upper limit of the number of adjacent zones that should be damaged. If you wish to limit the analysis by p-factor only, then specify the number of zones here (see min p-factor below). Specifies the minimum p-factor for which an analysis should be performed. The maximum a condition can contribute to the

Chapter 3 Using Stability

max. trim angle to consider Limit vertical extent of damage? max. vertical extent of damage Damaged side -Starboard or Port

Zone 1 located at bow or stern?

attained index is the p-factor. If the the p-factor is very small the contribution to the attained index will be negligible and there is little point in carrying out the analysis. Conditions whose pfactor is below this minimum will not be evaluated; this can speed up the analysis. If you wish the analysis to be purely limited by the number of adjacent zones (see above) then specify a small negative value. This will ensure that conditions with zero p-factor will still be evaluated. If the vessel trim exceeds this value, then the s-factor will be taken as zero (irrespective of the GZ curve). This can speed up the analysis. If desired the vertical extent of damage (when automatically generating the zone damage) can be limited. If desired the vertical extent of damage (when automatically generating the zone damage) can be limited. Specifies which side of the vessel will be damaged (when automatically generating the zone damage). The extent of damage is assumed to go all the way to the centreline but you may specify which side of the vessel is damaged. The heel direction in the Heel setup should correspond to the side of the vessel being damaged. It is normal to begin the Zone numbering at the stern, but the option to start from the bow is also allowed in Maxsurf Stability

Longitudinal Zone definition

The next table (Zones) allows for the definition of the longitudinal damage zones. Fore and aft extents of the zone boundaries are input by the user and the length and centre of the zone is automatically calculated; the boundaries of adjacent zones are automatically updated if required, as are the zone names. The subdivision length is taken as the limits of the length defined by the zones. As for other similar tables, use Edit | Add or Delete (or Ctrl+A or Del key, with a number of complete rows selected) to add or delete zones.

Damage zones defined by fwd and aft boundaries

Zones may be shown in the drawing views (this display option is only available in Probabilistic Damage analysis mode):

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Probabilistic damage zones (stbd. side damage) shown in pink. P-Factors

From the damage zone calculations, the probability of damaging a longitudinal zone or group of adjacent zones is calculated as well as the cumulative probability. The columns displayed depends on the choice of Resolution: MSC.216(82) or MSC.19(58) made in the Global table. All combinations of adjacent zones are calculated at this point. A subtotal for the pfactor for a given number of adjacent zones is given as well as a cumulative to total for all the p-factors. This will help the user to determine the maximum number of adjacent zones that should be analysed. In practice, it probably makes more sense to limit the analysis by specifying a desired minimum p-factor rather than a number of adjacent zones. This can easily be done by specifying the maximum number of adjacent zones as the number of zones defined. The last column shows whether a particular condition will be tested (if the p-factor is sufficiently large and the maximum number of adjacent zones is not exceeded).

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p-factor calculations for individual and groups of zones Sub zones due to transverse and vertical subdivision

As well as the main longitudinal subdivision, it is also possible to define sub-zones due to longitudinal bulkheads (transverse subdivision) and decks (vertical subdivision). Transverse sub-zone definition and R-Factors

Transverse sub-zone definition allows the user to limit the damage penetration to a certain distance into the vessel towards the centerline, measured from the side-shell. I have followed IMO notation by specifying the penetration depth from the side-shell (rather than specifying the offset from the centerline). A column is provided for the user to specify the side-shell offset (from the centerline) and this is used only to draw the transverse extents of the damage zone, the inner limit being at a distance side-shell offset minus b from the centreline. The side-shell offset value defaults to the maximum halfbeam of the vessel. The r-factors are then calculated for each of the b-values that have been defined. Note that there is one extra r-factor than the number of bulkheads – this represents the probability of damaging to the centerline. The sum of all r-factors should be unity (a check is provided). The b-values are defined for each individual zone, the b-values for multiple adjacent zones are calculated automatically.

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Longitudinal bulkhead definition and corresponding r-factors

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Visualisation of zones and sub-zones: sub-zones shown dashed; selected zone shown in bold.

The currently selected zone or sub-zone is shown in bold as well as any damage for that zone. This can also be seen in rendered view to quite effectively visualize the damage.

Clicking in a zone or sub-zone in the table highlights the zone graphically Vertical sub-zone definition and V-Factors

Similarly decks may be defined to create vertical subdivision of the zones. The corresponding v-factors are calculated, but these also depend on the draft of the vessel. Thus we introduce the concept of the currently selected Loadcase for the displayed vfactors. The loadcase for v-factor calculations is selected by clicking on the desired loadcase in the Global table. Note that during the full probabilistic damage analysis, the v-factors will be automatically recalculated for the loadcase under consideration.

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Loadcase for v-factor calculations is selected by clicking on the desired loadcase in the Global table.

Deck definition and corresponding v-factors Damage Specification

The damage to be used for the Probabilistic analysis is done in two stages. The first stage is to define the “Damage Spaces”. These are the compartments that are breached when the damge extends to fill the damage space defined by the longitudinal, transverse and vertical zone extents. The second stage is to determine the actual damage case that occurs when one or mode adjacent damage spaces are combined.

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Chapter 3 Using Stability “Damage Spaces” and “Prob. Damage Cases” tables Damage Spaces

“Damage spaces” are defined as the rooms that are wholly, or partially, contained within a cuboid defined by three pairs of orthogonal planes: aft, forward; top, bottom; and port, starboard. That is the rooms which will be breached if the vessel experiences damage to the cuboid defined by the planes. Both transversely and vertically the damage space is defined between adjacent boundaries (rather than in from the side-shell or up from the baseline). This will enable automatic generation of alternative damage cases, particularly in the event where there are rooms which span a longitudinal or horizontal boundary. Because of the definition of the Damge Spaces, there is no case which gives the full damage of the zone (ignoring transverse and vertical subdivision. For this reason it is necessary to define two damage spaces: one that defines the damage due to full transverse penetration; and a second for full vertical penetration. Damage spaces limited by transverse boundaries, these are listed b1, b2, etc as the penetration passes successive transverse boundaries (longitudinal bulkheads) and the final case, for full transverse penetration is labelled bx. Similarly, for vertical subdivision due to horizontal decks, these are labelled H1, H2, ... Hx; where Hx it the final Damage space corresponding to full vertical penetration. Once the zones, bulkheads and decks are defined the user can select the Case | Extent of damage command and this will automatically detect the breached rooms for a selected damage space according to which tanks lie (fully or partially) within the damage space boundaries. Once the automatic damage is defined, this can be modified by the user should this prove to be necessary (or it can be defined from scratch by the user). The “Damage Sapces” tab of the Damage window must be on top to enable this command.

Automatic definition of damage for each zone Alternative damage for vertical subdivision

Probabilistic damage requirements, as defined in Resolution MSC.216(82) and also MSC.19(58), allude to the fact that different combinations of damage should be considered.

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MSC.216(82) Regulation 7-2, Calculation of the factor si; p32:

This is expanded a bit in the explanatory notes:

MSC.281(85): Regulation 7-2.6; p26

The way this has been implemented in Maxsurf Stability is that alternative damage space definitions may be made for a given damage occurrence. Maxsurf Stability will then test the vessel under the different damage cases and select the one with the worst survivability factor. Although it is envisaged that this will be applied to cases where there is vertical subdivision due to horizontal watertight decks, the mechanism within Maxsurf Stability allows for the definition of alternative damage for any damage space. Some examples of the interpretation of this rule for single and multiple adjacent zone damage are shown below.

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Single zone flooding to uppermost deck:

Consider damage of Zone1 up to deck H13. Then all the rooms below this deck should be considered damaged:

But in addition, the lesser damage with C1 intact and also B1, C1 intact should also be considered to see which gives the lesser s-factor.

Similarly, if Zone2 is considered damaged, the alternative damage cases of A2 and B2 damaged and A2 only damage should be considered to find the minimum s-factor:

Multiple adjacent zone damage

For multiple adjacent zone damage, the damage location and extent must breach both zones. But the vertical extent may be varied. Zones 1 and 2 damaged up to deck H13 (=H22) gives four alternative damage cases that should be considered to find the minimum s-factor.

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Definition of alternative Damage Spaces

The alternative damage cases due to vertical subdivision by horizontal decks is created automatically. Should you wish for a certain damage case not to be evaluated, this can be achieved by deselecting the appropriate row in the Damage Case sheet. If all alternative damages should be excluded, this can be easily done with the option in the Global Probabilistic Damage table:

Alternative damage results

In the results, the alternative damages tested are shown. The damage case which gives the smallest s-factor is listed first and the alternatives shown below (in grey). The p, v, r values which are the same, are not repeated; the A-factor is given only for the damage case with minimum s-factor.

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Alternative damage cases tested Probabilistic Damage Cases sheet

Probabilistic Damage Cases sheet allows a review of all the damage cases to be evaluated during the probabilistic damage analysis to be made. Note that some damage cases may not be evaluated for all load cases. This could be because of minimum probability or maximum damaged length constraints or the fact that the watertight deck is below the upright, intact waterline for a given loadcase. If desired, it is possible to prevent selected damage cases from being evaluated. Because of the number of different damage cases, the data is shown transposed compared with the normal damage case presentation with one row, rather than a column, for each damage case.

The cases are generated from the damage space definition using the “List Prob.dam cases” or by running the analysis.

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Copying Probabilistic Damage Cases sheet

Additionally the user may automatically generate damage cases for the Zone damage that has been defined damage configurations within the maximum number of adjacent zones range and above the minimum p-factor will be added. This stage is not required for the probabilistic analysis, but has been added for convenience should the user wish to manually run large angle stability analyses for the same damage cases. The Damage window must be on top for this command to work. Damage cases will be added up to the maximum number of adjacent zones specified in the Global tab, if the pfactor exceeds the minimum values specified (again in the Global tab).

Automatic creation of damage cases using the damage defined for each zone Visualization of damage

When in Probabilistic damage analysis mode the damaged tanks and compartments displayed are not those of the current damage case, but those of the currently selected data in one of the Probabilistic Damage sheets: Clicking on a row in the “Zones” or “p Factors” tables will show the damge for a completely damaged longitudinal zone. Similarly when selecting a complete row in the “Long.Bhds” or “Decks” tables

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Clicking on a single cell in the “Long.Bhds” or “Decks” tables will select the damage in the space defined by the corresponding longitudinal bulkheads or decks (depending on the table)

Selecting a column in the “Damage Spaces” table will show the damage for that particular damage space:

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Finally selecting a row from the “Prob.Damage Cases” table will show the damage for that particular damage case:

Probabilistic damage permeabilities

It is possible to define different permeabilities to be used for tanks and compartments for the different load conditions – as required for “cargo compartments” in MSC.216(82) Regulation 7-3.2:

MSC.216(82) Regulation 7-3.2

Thess values are defined in the Permeabilities table in the Probabilistic Damage window. By default, the permeabilities are the same as the damage permeabilities given in the Compartment Definition table, but these can be overridden (for the probabilistic damage analysis only) for each draft if desired. When you generate new probabilistic damage data, the permeability values are copied from the Compartment definition, but they are not updated if they are then changed in the Compartment definition window.

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In the log file, the permeability used for any damaged tanks is shown:

Immersion of critical points at equilibrium

MSC.216(82) requires the s-value to be zero if, at equilibrium, certain critical points are immersed (Regulation 7-2 5.2 and 5.3:

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It is possible to include this check with the following two rows in the MSC.216(82) criterion:

New immersion criterion options for MSC.216(82) Probabilistic Damage

If rows 17 or 18 are ticked, Maxsurf Stability will compare the angle of equilibrium to the angle of immersion of the type of KeyPoints or KeyLine selected. If the equilibrium angle is not less than (>=) the immersion angle, the survivability index will be zero. Any type of KeyPoint (Downflooding, Potentinal downflooding, Immersion, etc.) or KeyLine (Deck edge, Marginline) may be selected (autocomplete is used).

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A results column gives the (minimum) immersion angle and Pass/Fail status (Pass if Equilibrium angle < Immersion angle; Fail if Equilibrium angle >= Immersion angle). If Failed, the s-factor is set to zero. If the Immersion angle cannot be found (no items of the selected type or insufficient heel angle range) then "n/a" is displayed.

Immersion results column for MSC.216(82) Probabilistic Damage Intermediate stages of flooding in Probabilistic damage analysis

It is now possible to define intermediate stages of flooding to be analysed when assessing the probabilistic damage performance of passenger ships (intermediate stages of flooding are not required for dry cargo vessels). Intermediate damage cases my have full flooded or partially flooded rooms. Summary

Since the probabilistic damage analysis is rather complex, the following gives a brief outline of how Hydromax performs the analysis: For each damage condition, Hydromax now automatically generates “alternative” damage which might arise due to vertical subdivision; for instance: intact rooms below the damage. When there are several “alternative” damages for a given probability of damage then the GZ curve needs to be evaluated for each of the alternatives and the one that give the minimum s-factor taken for that case to give the contribution to the attained index. Now for passenger vessels, it is also required to examine intermediate stages of flooding. These are additional “damage spaces” that may be defined by the user. The user may use this facility to define steps of progressive flooding from one room to another or can defined partially flooded rooms. For these intermediate stages, it is necessary to evaluate the GZ curve and determine sintermediate. There may be several intermediate stages defined so the one that gives the smallest value of s-intermediate should be taken. Additionally, the final stage can also be thought of a the final intermediate stage, so the value of s-intermediate from the final stage flooding should also be checked and the overall minimum value taken. The final s-factor is then the smaller of: all the s-intermediate values and the product of s-final . s-moment for the final stage of flooding. This s-factor needs to be computed for all the alternative damages and then that smallest s-factor used to calculate the contribution to the attained index.

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Definition of intermediate stages of damage.

This is done in the “Damage Space” table by selecting the “parent” damage space and selecting Add from the Case menu, at this point you can also specify the partial flooding percentage which will be applied to all damaged rooms:

The new intermediate case is added to the right of the selected case

You can specify default filling level to be applied to the damaged rooms in the intermediate stage.

In the intermediate stage, you can only edit the rooms that are damaged in the final stage.

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Example of definition of intermediate stages of flooding

Note that rooms which are intact in the final stage flooding cannot be damaged in an intermediate stage, though rooms which are damaged in the final stage my be intact in the intermediate stage. In the above example all final stage flooding shows fully damaged rooms and all intermediate stages have partially flooded rooms. However this is not enforced and it is possible to have partially flooded rooms in the final stage and fully flooded rooms in the intermediate stages if so desired. Combination of “damage spaces”

The damage space definitions are combined as usual to define all the damage cases which will be tested during the analysis. Use the List Prob.dam Cases command from the case menu to ensure that they are up to date.

Damage cases for single-zone damage

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When combining the intermediate stages, not all combinations of stages are taken. For example if two damage spaces that are to be combined each have two intermediate stages defined, then the first intermediate stage of each damage space are combined and then the second intermediate stage of the damage spaces. Thus giving only two intermediate stages to be considered. For example, looking at the situation in the above picture, to generate the damage up to Hx, the damage spaces H1 and Hx must be combined. Now each of these damage spaces has two intermediate stages defined. This gives rise to the final stage flooding condition as well as two intermediate flooding stage conditions. To further complicate things, there are also two alternative damage scenarios to be considered for damage up to Hx: one with all rooms from the base of the ship damaged and a second with the lower room intact. So when considering the damage condition for Z1Hx, we must evaluate GZ curves for the final stage damage and two intermediate stages each for two alternative damages! Results for intermediate stages of flooding

In the results presented below, random numbers between 0 and 0.999 have been generated for the various s-factors: s-intermediate, s-moment and s-final -- this is purely to aid in differentiating the numbers to aid explanation (in most cases the actual values would either be zero or unity).

Typical Prob.Dam. results (with artificial -random- s-factors)

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First of all, a new column “Case Type” has been added -- this indicates whether the case is a “Final stage of flooding” or an “Intermediate stage of flooding”. If the particular result is a Final stage of flooding and has the minimum S_factor, this is indicated with a “*” appended to the end; if it is an intermediate stage and has the minimum S_intermediate, then this is indicated by appending a “+”. Secondly, in the “Damage (tank indices)” column, partially flooded rooms have the letter “p” appended after their index. Note, the column heading will change to “Damage (room indices)” since we are using the word “room” to denote both tanks and compartments. Intermediate stages of flooding are shown in greyed italics. The resulting GZ curves are used only to evaluate s_intermediate. The final stage flooding conditions are shown in slightly darker grey and the final stage flooding condition which has the minimum value for the s_factor is the one that is take to give the A_factor for the particular probability of damage under analysis. Taking Z2; Hx damage in the above example, it can be seen that there are two alternative damage conditions to be compared (and the one that gives the minimum s_factor selected). These are Alt.1(2) and Alt.2(2). These alternatives are due to vertical subdivision and the fact that conditions with intact tanks below the damage should also be considered (as well as the fully damaged condition from the bottom up to the deck in question). In the example shown above, Alt.1(2) has the minimum s_factor so the corresponding result row is shown in black text; Alt.2(2) gave a higher value of s_factor so is shown in grey and there has no entry in the A_factor column since it does not contribute to the attained index. In determining which alternative has the minimum s_factor, it is first necessary to look at s_intermediate values of the final stage flooding and any intermediate stages that have been defined for the particular damage alternative under consideration. Looking at Alt.2(2), it is the intermediate case“Int.2(2)” which gives the smallest s_intermediate value (0.25011) -- this value is copied into the s_intermediate column of the final stage flooding of this damage alternative; the bracketed value being the s_intermediate value calculated from the final stage flooding GZ curve. The s_factor is then the minimum value of:  the smallest of all the s_intermediate values for the intermediate stages or the final stage

 the product of s_final ∙ s_moment for the final stage

This is done for all the alternative damages and the minimum s_factor selected. Probabilistic damage – Analysis

Once the analysis parameter data has been defined, it is worth checking that the heel direction (Analysis | Heel) is correct and also check that the s-factor calculation parameters are corerect (Analysis | Criteria) Pre-run checks

When trying to run the probabilistic damage analysis, Maxsurf Stability will make several checks to see if the analysis parameters have been correctly set up. These are not exhaustive tests but should pick up critical errors. The following checks are made:

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Chapter 3 Using Stability  That loadcases that have been specified exist  That the vessel type is correct in the criteria (if MSC.216(82) is being used)  That the correct s-factor criterion has been selected. Note that only one criterion may be selected. If Maxsurf Stability finds no criteria selected but a suitable one is available (but unselected) then it will prompt the user to use this one:

Analysis

Large angle stability analyses are computed for each combination of loadcase and zone damage up to either the specified maximum number of adjacent zones or the minimum specified p-factor. Basic data pertinent to calculation of the s-factor is also presented as well as a total Attained subdivision index at the bottom of the table. The required index is also shown as well as pass/fail status. Should the vessel sink, excessive trim occur or the large angle stability analysis fail to converge, this is reported and the s-factor given as zero.

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Probabilistic analysis results Probabilistic damage – Future developments

The probabilistic damage analysis is still under development and new features will be added in subsequent versions of Maxsurf Stability. Starting and Stopping Analyses

To start the analysis, choose Start Analysis from the Analysis menu or toolbar. Maxsurf Stability will step through the parameter ranges specified, floating the hull to equilibrium conditions where required. Maxsurf Stability will redraw the contents of the windows to display the current hull position for each iteration. Calculations may be interrupted at any time by selecting Stop Analysis from the Analysis menu or toolbar. If you have stopped the analysis, you can resume calculation by selecting Resume Analysis from the Analysis Menu or toolbar. There may be a slight time delay on all of these operations while the current cycle is finished. You can also switch application by clicking in the window of any background program. Maxsurf Stability will continue to calculate in the background although its speed will be reduced. The drawing of the vessel at each step of the analysis can be quite time consuming. If you are not interested in seeing the progress of the analysis, switch to a table window and maximise it to speed up the analysis. Should the analysis take longer than about 45 seconds, Maxsurf Stability will flash and beep to indicate that the analysis has been completed. The start, pause and resume functions are also available in the Analysis toolbar:

Probabilistic damage Log file

All the intermediate results, including all the GZ results and criteria evaluation for each loadcase / damage case combination are logged during the analysis. The logfile location is specified in the Preferences dialog:

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Probabilistic Damage analysis logging Probabilistic damage Log file: Key points results

The Key points results table is added to the log file just after the tabulated GZ data:

Probabilistic damage Log file: Alternative damage: min. s-factor

In the log-file the different damage cases within the zone-damage set will be listed if there is more than one to be tested. The Maxsurf Stability will generate a GZ curve for each of the damage cases and find the one that gives the minimum survivability factor:

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List of damage sets that will be examined.

Once the s-factors of all the damage cases have been evaluated, the lowest is selected and reported (all are listed in the log file):

The minimum survivability factor is found from the different damage sets tested.

Because of the reuse of previously calculated GZ curves, analysis of all the extra cases does not necessarily increase the overall computational time too significantly. Probabilistic damage Log file: Reuse of results:

Maxsurf Stability now checks to see if it has already calculated a GZ curve for the required loadcase and damage combination, this speeds up the calculation since repeat calculations of the GZ curve for the same conditions are avoided. In the log file a summary of all the conditions tested are listed at the end of the analysis of each loadcase:

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Normally in the log file, the GZ curve data is given after it has been calculated, followed by the evaluation of the s-factor criterion:

However, if the condition has already been evaluated, just the summary data are given:

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Batch Analysis Batch Analysis Concepts

Maxsurf Stability has basic batch processing capability. With a single command, Maxsurf Stability will run Large Angle Stability and Equilibrium analyses for all combinations of load and damage cases. Further, Limiting KG and KN calculations can be made for each damage condition. There are other options which allow the analysis to be performed heeling to both port and starboard. For the Limiting KG analysis you may also check the Limiting KG for each criterion individually. You may also choose to perform a Large Angle Stability and Equilibrium analysis at the final VCG. The aim of the batch processing function is to:  Provide the user with a simple and consistent way of carrying out Large Angle Stability and Equilibrium analyses on a large number of load and damage cases.

 Facilitate time consuming Limiting KG analyses, especially where results for all individual criteria are required.

 Enable Limiting KG and KN analyses to be performed automatically for all damage cases.

 Facilitate testing with heel to port and starboard for vessels with asymmetric loading and/or damage conditions (or hulls).

 Facilitate export of the data from Maxsurf Stability and import into MS Excel for post processing and report generation.

 Provide all relevant results and the data required to be able to reproduce the runs, i.e.: analysis parameters, file name etc.

Before you can perform a Batch Analysis it is recommended that you run a number of Analyses manually to check whether the Model has been defined correctly and all Analysis Settings and Environment conditions have been set correctly. Batch Analysis – Procedures

Once the loadcases, damage cases, key points, criteria and analysis parameters for the required analyses have been set up, the Batch Analysis is started

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Batch analysis runs all combination of loadcases and damage cases.

Tip: Under most operating systems, minimising Maxsurf Stability can reduce the time required to perform the calculations. This is because time consuming redrawing of the design windows, graphs and tables is avoided. Batch Analysis Settings

Analysis parameters such as trim, heel angles etc. are set in the normal way for each analysis type included in the Batch analysis. For example, if you want the Large Angle Stability to use a fixed trim of 0.5 m:  first select the Large Angle Stability analysis type from the analysis menu  set the trim to Fixed trim and 0.5 m  then select Analysis | Batch Analysis Batch Analysis Environment Options (Criteria)

Any Analysis Environment Options specified prior to a Batch Analysis will be used during the Batch Analysis. Any criteria that have been set are evaluated at the end of each analysis and the results of these are also output to the text file.

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Important: For important information on varying displacement while evaluating criteria, see Important note: heeling arm criteria dependent on displacement on page 290. Batch Analysis Results

Before analysis starts, you will be prompted to enter the name and location of the file where Maxsurf Stability will write the results of the batch analysis. Once the analysis is complete, this tab delimited text file may be imported directly into MS Excel for further processing. Because the analyses are simply carried out one after the other, it is not possible to go back to the results for a specific analysis from within Maxsurf Stability; only the results of the final analysis will be stored in Maxsurf Stability. At the bottom of the dialog is a check box which allows users to select whether the results of a batch analysis should go to the Report window in Maxsurf Stability as well as the batch analysis text file. When the option for Sending the results to Word is selected in the Edit | Preferences dialog, the batch analysis will automatically create a Word document. Warning: Sending the results to the Report can slow down analysis considerably and also consume considerable system resources. For large batch analysis, it is advisable not to include the results in the report. The report is stored in memory and if you have insufficient memory, it is possible that your computer will become very slow to respond and under some circumstances with certain operating systems even cause Maxsurf Stability to crash. Also see: Reporting on page 201.

Analysis Settings In the previous sections opening and preparing a model in Maxsurf Stability was discussed together with descriptions of the different Analysis types. This section will describe the following analysis settings:  Heel  Trim  Draft  Displacement  Specified Conditions  Permeability  Tolerances

Maxsurf Stability will allow specification of only those analysis settings that apply to the currently selected analysis type.

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In hydrostatic analysis, there are three degrees of freedom: Trim, Heel and Draft. Maxsurf Stability matches the trim, heel and draft with the vessel’s mass and centre of gravity or visa versa. This way the volume of the displaced hull matches the required mass and the centres of gravity and buoyancy lie one above the other in a vertical line. For example: it can match a specified heel, trim and draft by varying the displacement and centre of gravity; or it can match a specified displacement and centre of gravity by varying the heel, trim and draft. Combinations of both are also possible. The following table is a very simplified representation of the degrees of freedom and their weight counterpart:

1 2 3

Degree of Freedom Draft Trim Heel

Weight Displacement Longitudinal Centre of Gravity (LCG) Transverse Centre of Gravity (TCG)

In fact it is a rather more complicated situation than that suggested by the table above, because vertical centre of gravity is also important and also because most of the variables are coupled. The various analysis types and settings can be thought of as setting one variable in each pair to a fixed value and deriving the others from the analysis. For example: the Upright Hydrostatics analysis consists of fixing heel and trim and stepping through a series of fixed drafts. In this case the LCB and TCB (and therefore the required LCG and TCG) are calculated from the underwater hullshape at each draft. For an equilibrium analysis all degrees of freedom are derived from the centre of gravity and Displacement. In the Specified Condition Analysis any combination of the variable pairs may be specified. Heel

The Heel dialog from the analysis menu is used to specify the range of heel angles to be used for Large Angle Stability, KN and Limiting KG analyses. Heel angles between 180 and +180 may be specified. The heel steps must be positive. If only one set of steps is required, simply put 0 in the other steps. If there is any asymmetry in the vessel due to either: hull shape, key points, loading, damage, etc., and there is any doubt as to which will be the worst heel direction, then the analysis should be carried out for both heel to starboard and heel to port to find the most pessimistic condition. If all the heel angle intervals are 10 deg or less, Maxsurf Stability will fit a cubic spline to the GZ curve and use this to interpolate for values between the tested heel angles. If any step is greater than 10 deg, Maxsurf Stability will not do any curve fitting and linear interpolation will be used.

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Note: For the angle of equilibrium to be found (when analysing criteria), it is essential that the GZ curve crosses the GZ=0 axis with positive slope. It is possible that the GZ at zero heel may be very slightly positive (due to asymmetry or rounding error) for this reason, it is advisable to test at least one negative heel angle, at say -5 degrees, to ensure that the equilibrium angle is identified. It is good practise to start the heel range at an angle of approximately -30°. This is to allow roll back angle criteria to be evaluated correctly.

Note: The heel angles to be used are specified independently for each analysis mode. This can be a source of apparent differences in the results from the different analyses. Trim

For most analyses you may specify whether the vessel is free-to-trim or has fixed trim. Select Trim in the Analysis menu to bring up the Trim dialog. Trim may be specified for Upright Hydrostatics, Large Angle Stability, KN Analysis Limiting KG, Floodable Length and Tank Calibrations. (For the Specified Condition analysis, the trim may be specified in the Specified Conditions dialog.) Equilibrium and Longitudinal Strength analyses always use a free trimming (and free heeling) analysis so that there is no trimming (or heeling) moment applied to the vessel at the final equilibrium. Essentially there are three options for trim: 1. Fixed trim – the analysis is carried out at a fixed, specified initial trim. This applies to all analyses that carry out a large angle stability-type analysis (Large Angle Stability, Limiting KG, KN, Probabilistic Damage) as well as Upright Hydrostatics and Tank Calibrations 2. Free to trim to loadcase – the analysis trims the vessel to the CG specified in the loadcase. This option is available for all analyses that have a loadcase: Large Angle Stability, Equilibrium, Longitudinal Strength, Probabilistic Damage.

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3. Free to trim to specified CG – this is again free-to-trim but the CG is specified in the dialog. This is for when a range of displacements is used for the analysis: Limiting KG, KN, Floodable Length. In this case, all three components of the CG need to be know. This it is possible to specify the LCG either directly or so that the upright, intact vessel floats at a specified trim. The TCG and VCG are specified directly. In the case of the Limiting KG analysis, the VCG is being found by the analysis, so cannot be specified. For the Floodable Length analysis, heel is not considered thus TCG cannot be specified.

Specification of different trim options is dependent on the type of analysis currently selected.

Fixed trim (KN and Limiting KG analyses only). The analysis is carried out with the specified fixed trim; the vessel is not free-totrim as it heels. Although considerably faster, this analysis will tend to overestimate ship stability properties such as GZ. Free-to-trim using a specified initial trim value Using this method, for each displacement, the LCB of the intact vessel at the specified trim and zero heel is computed. The LCG is calculated using this value and the VCG. Calculations at each heel angle of the large angle stability analysis are then done free-to-trim using the derived LCG and VCG. Thus, for each displacement, the upright, intact vessel trim will be the same, but the LCG will be different. Free-to-trim to a specified LCG value With this method, a specified constant LCG is maintained for each displacement. This LCG is then used to compute the free-to-trim vessel orientation at each heel angle as the large angle stability analysis is performed. Thus, for each displacement, the LCG will be the same, but the upright vessel trim will be different.

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VCG for trim balance The VCG, measured from the vertical zero datum (not necessarily KG), may be specified. For KN analysis, the VCG will only have an effect if the analysis is free-to-trim. It will be used to determine the LCG if an initial trim value is specified. It will also be used to improve the accuracy of the KN results. For Floodable Length calculations, which are always calculated free-to-trim, the VCG will be used to calculate the LCG if an initial trim value is specified. Also, because the analysis is very sensitive to trim, the VCG is needed to provide an accurate balance of the trimming moment. (As the trim angle increases the longitudinal movement of the centre of gravity due to its vertical position becomes more important.) In the case of the Limiting KG analysis, the actual VCG is used and the VCG input field will state “not applicable”. TCG value The TCG option allows you to specify an off-centreline centre of gravity for Limiting KG and KN calculations. This is especially useful when evaluating the Limiting KG of a damaged vessel that had cargo or ballast in tanks which are subsequently damaged. The TCG can be either specified directly or calculated from the tank loadings defined in the current loadcase. Current Loadcase specifies initial loading of damaged tanks (los mass during analysis)

Finally, for the Limiting KG analysis, there is an option to automatically adjust the displacement and LCG of the vessel so that liquid cargo of damaged tanks is removed from the model. This is for consistency with the lost buoyancy analysis method: the buoyancy contribution of damaged tanks is removed from the model, so to be consistent, any liquid cargo should also be removed from the model. Draft

The draft dialog is used to specify the range of drafts to be used for the Upright hydrostatics analysis.

The VCG specified in the draft dialog is used for the calculation of upright stability characteristics such as GMt only, and is specified in terms of KG – i.e. from the baseline, which is not necessarily the vertical zero datum. Displacement

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Specified Conditions

The specified conditions analysis setting is only available for the specified condition analysis. See Specified Conditions on page 118. Permeability

The Permeabilities are set in a table in the Permeability dialog. Use the Add and Delete buttons to add or delete rows from the table. The permeabilities may be sorted by double clicking on the permeability column heading. The last set of permeabilities used will be recalled from the registry when Maxsurf Stability is started.

The Permeability dialog is used to specify the permeabilities to be used for the Floodable Length analysis; the permeability is applied over the entire length of the vessel. This permeability is unrelated to compartment, tank or non-buoyant volume permeability and is only used for floodable length calculations. Individual Permeability of Tanks and Compartments

The individual permeability of each compartment (or tank) is specified in the Compartment definition table. The compartment, tank and non-buoyant volume permeabilities are used when calculating the effects of damage, and/or calculating the weights of fluids in tanks in the loadcase. Also see: Modelling Compartments on page 59 Tolerances

In the Edit | Preferences dialog, calculation tolerances can be set. This defines the tolerances that Maxsurf Stability uses to determine when to finish iteration during

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Ideal tolerances can range between 0.00001% and 0.1% (1 gram in 10 tonnes of displacement). Acceptable tolerances can range from 0.001% to 1.0%. Acceptable tolerances should always be greater than Ideal tolerances. Convergence Error

Maxsurf Stability will attempt to solve most analysis to within the ideal tolerance. If this is not achieved within a certain number of iterations, but the acceptable error has been achieved, Maxsurf Stability will continue. If convergence to within the acceptable error has not been achieved, Maxsurf Stability will display a warning.

One of the most common causes of non-convergence is if the specified displacement exceeds the volume of the completely submerged vessel and it sinks. Also convergence may be poor if the trim angle approaches 90. If Maxsurf Stability thinks that it is likely that the model has sunk (waterplane area is zero at the current condition) the following dialog will be displayed. The specified displacement and the actual displacement at the current iteration are provided for information. Note This warning is not displayed during batch analysis, instead the warning is written in the batch file. The warning is also not shown when accessing Maxsurf Stability from a VBA macro using the Automation interface If there is a convergence problem, which appears not to be due to sinking, then the following dialog will be displayed.

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This problem can sometimes occur if the specified displacement is extremely small and the vessel has a large flat bottom, producing a highly non-linear waterplane area vs. draft plot. Other causes of non-convergence can be non-linear moment to trim vs. trim angle curve or moment to heel vs. heel angle curve. Note: There are occasions when convergence will not necessarily occur within the maximum allowable number of iterations. If Maxsurf Stability fails to converge it will give you a warning, but will allow you the option of continuing the search. If you choose to continue, Maxsurf Stability will search for the equilibrium position indefinitely. If the search is unsuccessful after a reasonable period of time, you can interrupt Maxsurf Stability by pausing the analysis. The analysis will also fail to converge if the trim becomes excessive. All analyses other than Floodable Length will fail if the trim exceeds +/-45º; in the case of the Floodable Length analysis, this limit is increased to +/-89º.

Analysis Environment Options The analysis can be performed in different environments; this section describes the analysis environment options available in Maxsurf Stability in more detail:

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Chapter 3 Using Stability  Fluids Analysis Methods  Density  Hog and Sag  Waveform  Grounding  Stability Criteria  Damage Fluids Analysis Methods

Maxsurf Stability allows you to specify two different ways of simulating any fluids contained in tanks or compartments. Selecting Fluids in the Analysis menu opens the Fluids Analysis dialog. It is possible to specify the range of filling levels for which free surface moments should be applied in the loadcase. This functionality is accessed through the Analysis | Fluids dialog:

Fluid Analysis dialog

If the corrected the VCG method is used, the FSM is applied if the filling level is within the exclusive range specified; i.e. if the filling level is less than or equal to the lower limit or the filling level is greater than or equal to the upper limit, the free surface moment will be zero. The upper limit is clearly stated by IMO as 98%, but the code provides some flexibility in interpretation for the lower limit. You may set different limits for each of the different free surface moment types other than “User Specified”. (see IMO IS Code) 3.3.2 Free surface effects should be considered whenever the filling level in a tank is less than 98% of full condition. Free surface effects need not be considered where a tank is nominally full ,i.e. filling level is 98% or above.

3.3.10 The usual remainder of liquids in empty tanks need not be taken into account in calculating the corrections, provided that the total of such residual liquids does not constitute a significant free surface effect. In addition it is possible to ignore the free surface moment if the VCG correction for a single tank, due to the free surface moment is less than a specified amount. This requires that a nominal minimum displacement be specified. This is applicable to the “IMO” free surface moment type only. (see IMO IS Code) Page 193

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3.3.9 Small tanks which satisfy the following condition using the values of “k” corresponding to an angle of inclination of 30°, need not be included in the correction:

M fs /  min  0.01m where M fs is the free surface moment of the tank in question and  min is the ship displacement at the minimum mean service draft of the ship without cargo, with 10% stores and minimum water ballast, if required. Note: Tank Calibration results In the tank calibration results the free-surface moment based on the transverse second moment of area of the tank waterplane is given for all filling levels. This is because the actual free surface moment to be used to determine the VCG in a loadcase depends on the method being used and also the heel angle in question (in the case of the IMO correction).

Note: Calculation of GM GM values always use the centre of gravity corrected for free surface moments even if the “simulate fluid” option has been chosen. Note that the upright free surface moments as shown in the loadcase are used, not those from the actual second moment of area of the inclined tank waterplane.

Note Most documented stability criteria assume that the corrected VCG method has been used. Although the computational potential is available, authorities have not adopted this more accurate calculation of the shift in centre of gravity due to fluid movement. Fluid analysis method: Use corrected VCG

Tank capacities and free surface moments are calculated for the upright hull (zero trim and zero heel). The effective rise in VCG due to the tanks’ free surface is calculated by summing the free surface moment of all the tanks and dividing by the total vessel displacement (the free surface moment to be applied is specified in the loadcase). This method should be used when compiling a stability booklet for a design, as it corresponds with the traditional approach used by naval architects and classification societies worldwide. It is reasonably accurate at low angles of heel and trim. In this case, the loading window will include a column for free surface moment and cells for corrected fluid VCG. These values are automatically calculated from the maximum free surface moments of the tanks, calculated in the upright condition. There are several FSM types available. For more information, see Working with Loadcases on page 43.

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Fluid analysis method: Simulate fluid movement

This method is a faithful simulation of the static movement of the centre of gravity of the fluid in each tank. Every tank is rotated to the heel and trim angle being analysed. Maxsurf Stability iterates to find the fluid level for the rotated tank at the specified capacity. The new centre of gravity is calculated for each tank and used in the analysis. The new LCG, VCG and TCG are calculated for the whole design and used in the calculation of GZ, KG, and GM. This approach is used when the stability of a vessel is being investigated and the closest possible simulation of the hull’s behaviour is required. It is particularly useful at high angles of heel or trim, or with tanks whose heeled water plane area may be significantly different from the upright case (i.e. tall narrow tanks, or wide shallow tanks). The penalty of using this approach is that the calculation time is longer, however the results are significantly more accurate.

When fluid simulation method is selected, free surface moments and corrected fluid VCG are normally not displayed in the loadcase.

When selected, fluid simulation is used for analyses that use a loadcase, i.e. Large Angle Stability, Equilibrium Condition and Longitudinal Strength (the Longitudinal Strength analysis always uses fluid simulation). When fluid simulation is used in one of these analyses, the actual fluid level in the tank, filled to the volume specified in the loadcase, will be displayed in the View window. Otherwise the complete tank will be shown. Density of Fluids

Where necessary, the density of sea water (the fluid in which the vessel is floating) and fluids commonly carried on board can be adjusted using the Density dialog. Density using the current units, or non-dimensional relative density (specific gravity), may be specified. Alternatively, density may be specified using Barrels as the unit of volume. Conversions are performed automatically. Specific gravity is calculated relative to a fluid having a density of 1000.0 kg/m3.

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By assigning a code to the fluid you can easily apply the fluid type in the Compartment Definitions table. Tanks that have been specified as containing one of these fluids will be updated automatically when the density of the fluid is changed in the Density dialog. Tank calibrations results and loading conditions will also be updated. Note The vessel’s hydrostatics are always calculated assuming the vessel is floating in the fluid labelled “Sea Water”. This is the first fluid in the list printed in bold font. If the vessel is to float in a different fluid, it is necessary to change the density of this fluid. Note that only the custom fluids may have their names changed. Thus, if you wanted to carry out an analysis for a vessel in fresh water, you would change the density of “Sea Water” to 1000.0 kg/m3. Saving and Loading Densities

Densities listed in the Density table can be saved and loaded using the File menu. The densities file may be edited manually if desired. There is one row for each of the 18 fluid types. The four columns, each separated by a tab character. These are fluid name, fluid code, specific gravity, colour respectively (the colour is in hexadecimal for the red, green, blue components and are probably much more easily edited in the Density dialog. The name and code for the first entry, Sea Water, cannot be changed (any changes made will be ignored). All other entries may be edited (the same restrictions area applied as when editing through the Density dialog). Sea Water Water Ballast Fresh Water Diesel Fuel Oil Lube Oil ANS Crude Gasoline leaded

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S B W D F L C G

1.0250 1.0250 1.0000 0.8400 0.9443 0.9200 0.8883 0.7499

6D00FF00FF00 6D006D00FF00 FF005F005F00 FF005B00FF00 6D00FF006D00 7F007F007F00 3F003F003F00 FF0000007F00

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Unlead. Gas. JFA MTBE Gasoil Slops Custom 1 Custom 2 Custom 3 Custom 4 Custom 5

U J M GO SL C1 C2 C3 C4 C5

0.7499 0.8203 0.7471 0.8524 0.9130 1.0000 1.0000 1.0000 1.0000 1.0000

FF007F007F00 7F007F00FF00 F600FA00C900 FF00FF007F00 FF006F00FF00 D6000300D600 D600D6000300 0300D600D600 D60003000300 DF00DF00DF00

If you make an error, you can always reset the densities to their default values in the Densities dialog. Also see: Windows Registry on page 16 Hog and Sag

Hog and sag have been reinstated in Hydromax. However the implementation is quite different than before. Hog and Sag are now modelled by moving the waterline rather than deforming the hull. This means that it is more akin to the vessel bending under the differential mass and buoyancy distribution rather than accounting for a permanent set in the hull due to construction (or, in the case of a sailing yacht, rig tension). This means that the applied waterline change due to hog and sag does not change as the vessel trims or heels. Below, Upright Hydrostatics with and without trim are shown with 1m of hog applied (note that during hog the ends of the vessel are immersed more deeply; for sag, the middle of the vessel is immersed more deeply):

1m hog with zero trim

1m hog with 0.5m trim by the stern

Waveform

Maxsurf Stability is capable of analysing hydrostatics and stability in arbitrary waveforms as well as for a level water plane. To specify a waveform, select the Waveform command from the Analysis menu:

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The water plane can be specified as flat, or as a sinusoidal or trochoidal waveform. If a waveform is specified, the wavelength, wave height and phase offset can be specified. The wavelength defaults to the waterline length of the hull at the DWL. If the wavelength is modified the wave height defaults to a value in metres of: Wave height [m] = 0.607 √ Wavelength [m] This is the metric equivalent of the US Naval standard wave height: Wave height [ft] = 1.1 √ Wavelength [ft] For short waves of wavelength less than 64m, the waveheight reduces linearly with wavelength given by the formula: Wave height = 0.075875 Wavelength

Once a wavelength has been set, the wave height may be modified. The phase offset governs the position of the wave crest aft of the forward end of the DWL, as a proportion of the wavelength. The phase offset varies between 0 and 1, both of which correspond to a wave crest at the forward end of the DWL.

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For example, a phase offset of 0.5, with a wavelength equal to the waterline length, will give a single wave crest at amidships. Grounding

Grounding is an additional analysis environment option for the Equilibrium or Longitudinal Strength analysis. It is possible to specify grounding on one or two points of variable length. The Equilibrium analysis will determine whether the hull is grounded or free floating and will trim the hull accordingly. Damage can be specified concurrently with grounding. If the vessel touches one or both grounding points, this will be reflected in the results: The displacement column will show the total grounding reaction force in brackets; the sum of the buoyancy and the grounding reactions equals the loadcase displacement.

The effective centre of gravity will be modified by the grounding reactions – a mass is effectively being removed from the vessel; this will bring the effective centres of gravity and the centre of buoyancy in line vertically. The value of KG, GMt and GMl are all calculated to the effective centre of gravity. Remember that KG is measured in the upright vessel reference frame (normal to the baseline); whilst GMt and GMl are the actual vertical separation of the metacentres above the centre of gravity in the trimmed reference frame normal to the sea surface.

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Note: Grounding points are considered to span the transverse extents of the hull and therefore constrain the heel to zero. The length of the grounding points is only used when considering the load distribution for Longitudinal Strength analysis and not to determine the pivot point. The vessel is considered to pivot at the centre of the grounding point. When two grounding points are entered, the first point (edit boxes on the left) must refer to the forward grounding point; the second grounding point is the aft grounding point.

Note: Fixed zero heel during grounding analysis The equilibrium analysis will only consider the longitudinal balance of moments, i.e. the vessel will not be balanced in heel and the vessel will remain upright (zero heel) even if the transverse metacentric height is less than zero. Stability Criteria

Stability criteria may be seen as the “environment of authorities” that the ship will be deployed in. For more information see Chapter 4 Stability Criteria starting at page 209. Damage

You can specify whether the model is to be analysed in intact or damaged condition using the Analysis Toolbar. Also see: Damage Case Definition on page 80

Analysis Output Maxsurf Stability will produce the following output data:  Maxsurf Stability model visualisation  Result data tables per analysis  Graphs per analysis  Report o

Report window

o

Streamed directly to a Word document

o

Report Templates

In this section:

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Chapter 3 Using Stability  Reporting  Copying  Select View from Analysis Data  Saving the Maxsurf Stability Design  Exporting Reporting

Maxsurf Stability has several options to do your reporting:  Batch Analysis text file and/or streaming to Report window  Automatically generate a report in the Report Window for each analysis run  Automatically Streaming results to Word  Manually copy and paste tables and graphs from the Results Window and Graph Window

The most efficient method depends on the number of loadcases and damage cases you have to analyse and the output you require. Form small number of loadcases and damage cases you can do a manual copy and paste of the results into a report. This then allows you to validate the results at the same time. For large numbers of cases, it is recommended to use batch analysis. Batch Analysis results saved as text files do not include graphs. Select the option to send the results to the report window if you require Graphs. Additionally, if the option to Stream the report to Word has been selected in the Edit | Preferences dialog a word document is automatically generated after a Batch Analysis. Streaming results to Word

It is possible to stream the Analysis results directly to Word. To do this:  Edit | Preferences  Select the option to Send the Report to Word

This will send the Report document to Word instead of to the Report window. After you have run an analysis a Word document is created and opened automatically. This also applies to Batch Analysis. Inserting tank plans in reports

Tags may be included in the report template (see below) to insert tank plan drawings into the report.. These are as follows: Report Templates

Maxsurf Stability offers the ability to customise reports through a Report Template. This feature is only available when sending reports to Microsoft Word. With report templates, instead of just dumping the results of each analysis into a Word document, it is possible to use template keywords to specify where in the document the analysis results go and where each element of the output (such as graph, tables, etc) is placed.

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This gives you much greater control over how the analysis results are output than with the normal Send Report to Word option and allows you to customise your own report template document. To turn on Report Templating you need to select it in the Preferences dialog box. Simply tick the box ‘Use Word Templating’. Please note that Send Report to Word must be enabled before you can enable this option. See the dialog box below as an example:

The Word Template File specified should be in .dot or .dotx/dotm (for Word 2007) format and will be used when creating any future reports. You can use one of the sample templates provided, or you can build your own template. Two Report Templates have been included to get you started: StabilityBooklet.dot This is an example of a complete Stability Booklet template – this document is the default Word Template file for new users and is recommend for users wanting to quickly create a Stability Booklet. Users can start with StabilityBootlet.dot and then use it customise their own report template. HMReportTemplate.dot This document is a good starting point for creating your own customised template. It contains an introduction to how templates are created and configured. It also includes all of the basic analysis blocks and variables to get you started.

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Both of these templates contain macros and toolbar items to make life easier when you design your own template. These allow you to easily add and remove the analysis keyword blocks.

Note: To edit a report template in Microsoft Word you will need to start Microsoft Word and then open the template directly using the File menu. Simply double-clicking on a template document opens up a new document based on the template (which is not what you want).

The location of these report templates varies depending on which operating system you are using. On Windows XP/Server 2003 the default location for the report templates is:  C:\Program Files\Maxsurf 14\Report Templates\ On Windows Vista, due to new security changes we’ve had to move this to an alternative location that every user has write access to – so you can find it at:  C:\Users\Public\Documents\Maxsurf\Maxsurf14\Report Templates\ Tips:

See: Copying Tables on page 203 for tips on how to include the table header in a copy paste to for example Excel Graph Formatting on page 237 for tips on how to format your graph prior to copying to another application. Data Format on page 255 for tips on how to specify what should be displayed and customise how to display tables (vertical or horizontal). Copying & Printing

A range of options for transferring data from Maxsurf Stability to other programs such as spreadsheets and word processors is provided through copy and paste functions. This data transfer works both ways: e.g. copying and pasting data to and from Excel spreadsheets allows you to use the full spreadsheet capabilities of Excel on your Maxsurf Stability model. Copying Hull Views

Pictures of the hull in the View windows may be copied to the Clipboard using the Copy command from the Edit menu. The image copied is as per the image displayed in the Maxsurf Stability view window. These pictures can then be pasted into other applications or the Maxsurf Stability Report window. To copy a simple bitmap image of the view at the current resolution, use Ctrl+I; additionally, a bitmap of the current image may be saved by pressing Ctrl+Shift+I Copying Tables

Tables may be copied to the clipboard. Simply select a cell, row, column, range of cells or the whole table and then choose the Copy command or Ctrl+C.

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The data copied from the table will be placed on the clipboard and can then be pasted into a spreadsheet or word processor for further work. Note: Copying data from the table with the Shift key depressed, will also copy the column headings. Printing

Each of the windows in Maxsurf Stability may be printed. Simply bring the window you wish to print to the front and choose Print from the File menu. Views of the hull in the View window may be printed to scale as in Maxsurf. Prior to printing you may wish to set up the paper size and orientation by using the Page Setup command from the File menu. Print Preview

The page to be printed is initially displayed in print preview mode. To print the page click the Print button, otherwise click the Cancel button. The printing may be forced to be black and white. Choose the Colours button and select the options required. Note that the print preview is not refreshed after these changes, but the selection will be reflected in the printout. The titles may be edited by clicking the Titles button. Graph Printing to Scale

When printing the graph, it is possible to ensure that the graph is plotted to a sensible scale so that measurements can be made directly from the graph. To do this, hold the shift key down when selecting the print command for the graph. You will be asked if you want to print the graph to scale or to fill the page:

The scale used will depend on the length units that are currently selected. If these are metric, then the graph will be plotted so that the grid lines are at one of the following intervals (If the current length units are imperial then similar intervals will be used, but they will be inches instead of cm.): 1.0cm, 2.0cm, 2.5cm, 5.0cm. Exporting a Bitmap Image

You may also export a bitmap of the rendered perspective view with the File | Export | Bitmap Image command. Select View from Analysis Data

For most analyses, each step from the analysis can be visualised when the analysis has completed. For example: the angle of downflooding can be visualised by returning to the Stability table in the results window, selecting the column at the required heel angle and select “Select View From Data” in the Display menu.

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In the View window the hull will be displayed in the selected position. This can also be done for Upright Hydrostatics and the different wave phase calculations for an Equilibrium analysis in a waveform. The Select View from Data can also be used to display the Curve of Areas graph for each intermediate analysis stage, see Graph type on page 236. Saving the Maxsurf Stability Design

Maxsurf Stability design data may be saved  Saving in a Maxsurf Stability Design File  Saving Input Files separately Saving in a Maxsurf Stability Design File

To save the design in one file, ensure that the View window is topmost and select Save from the File menu. The Maxsurf Stability data is saved in a .hmd file with the same name as the design. Saving Input Files separately

In addition to saving all the data together, the data in the individual tables such as loadcases, damage cases, compartment definition, key points etc., may also be saved separately. For more information on file properties and extensions in Maxsurf Stability, please see: File Extension Reference Table on page 356. Note Although all Maxsurf Stability model data is saved in the .hmd file automatically every time you press Save from any of the design windows, it is recommended to also save the Maxsurf Stability input files separately. This gives the option of loading common data into different design files. E.g. for comparing the characteristics of vessels which have only minor differences in hull shape and identical tank layouts and loadcases. Saving Loadcases to a File Once you have set up a loading spreadsheet, you can save it in a file on disk. This allows the same loading spreadsheet to be recalled at any time for use with the same design or with any other hull. To save the loadcase table, ensure the Loadcase window is topmost on the screen and choose Save Load Case from the File Menu. Selecting this option saves all the loads displayed in the current tab in the Loadcase window. Saving Damage Cases to a File Bring the Damage window to the front and select Save Damage Cases or Save Damage Cases As from the file menu.

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Saving Compartment Definitions to a File To save a compartment definition to a file, bring the Input window to the front and choose the compartment definition table; select Save Compartment Definition from the File menu. You will be asked to name the file and select where it is to be saved. Saving Input Window Tables To save a input window table to a file, bring the Input window to the front and choose the required input table; select Save from the File menu. You will be asked to name the file and select where it is to be saved. Saving Results to a File

Once you have performed an analysis, the data generated may be saved as a text file. This allows for further calculations to be done in a spreadsheet or for formatting to be done in Word, Excel or other programs. To save the data, ensure the Results window is topmost on the screen and choose the table containing the data you wish to save. Select Save or Save As from the File Menu. Selecting this option saves all the data currently displayed in the Results window. The Results files are saved as tab delimited text, meaning that they can be read directly into spreadsheets such as Excel with values being placed in individual spreadsheet cells. Exporting

The data export function in Maxsurf Stability is similar to Maxsurf. Some Maxsurf Stability-specific export features are described below.

Data export dialog in Maxsurf Stability.

DXF export Contains all lines displayed in the active design window as closed poly-lines. In addition, each tank, compartment and non-buoyant volume is exported on a separate layer. This export function is particularly useful to export tank arrangement drawings. Note: The layer name is the same as the compartment name, so it is important to have unique compartment names.

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For more information on data export of DXF and IGES, please see the “Output of Data” section in the Maxsurf manual. Results graphs may also be exported to a DXF file. Exporting the Model to Maxsurf Stability Version 8.0

After Maxsurf Stability version 8, a major change to the Maxsurf Stability file structure was made. Maxsurf Stability models created in versions greater than version 8.0 can be exported using the File | Export menu so that it is compatible with Maxsurf Stability version 8.0. All key points will become downflooding points in the version 8 file and any tank sounding pipe information will be lost.

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Chapter 4 Stability Criteria This chapter describes how stability criteria are used in Maxsurf Stability. Stability criteria are evaluated for Large Angle Stability, Equilibrium and Limiting KG calculations. A fixed sub-set of criteria is used for the Floodable length analysis and these criteria are accessed in their own, simplified dialog. The following sections will be discussed:  Criteria Concepts, an overview of what capabilities Maxsurf Stability offers with regards to stability criteria.

 Criteria Procedures, explanation how to work with the Maxsurf Stability criteria dialog to create your own custom set of criteria.

 Criteria Results, criteria evaluation results  Nomenclature, explanation of terms and definitions

See also:  Appendix B: Criteria file format  Appendix C: Criteria Help  Appendix D: Specific Criteria

Criteria Concepts Maxsurf Stability includes a wide range of template criteria (or: parent criteria) as well as pre-defined custom criteria such as IMO, HSC, DNV, ISO and more. Maxsurf Stability uses a single dialog to control all the stability criteria. This makes it quick and easy to set which criteria should be included for analysis and to change criteria parameters. It is also possible for users to create their own custom sets of criteria. Users may save, import and edit their criteria sets. These custom criteria files may be easily transferred via email. Criteria may be identified as intact or damage criteria (or both). This ensures that the correct criteria are evaluated and displayed during normal and batch analysis. Although all criteria are displayed in the criteria table, only criteria that are applicable are added to the report; i.e.: if the intact case is being computed, only the criteria that are selected for evaluation during an intact analysis will be evaluated and added to the report, similarly for the damage cases. Criteria results are added to the Report after a Large Angle Stability or Equilibrium analysis. However, only the applicable criteria are added to the report (although all are displayed in the Results table); i.e. after an Equilibrium analysis only those criteria that are evaluated from Equilibrium data are added, and after a Large Angle Stability analysis only GZ based criteria are added to the report. Help information relating to the use and parameters of each criterion is displayed in the lower right hand corner of the dialog.

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Criteria List Overview

Maxsurf Stability includes a wide range of criteria. These criteria are listed using in a tree control on the left-hand side of the criteria dialog. This section describes how this list of criteria can be divided up in to Parent heeling arms, Parent criteria, predefined custom criteria and user created custom criteria. This section also explains how all criteria can be divided up into two different criteria types: equilibrium and GZ curve based.

The criteria tree list

Parent Calculations This folder contains calculations that are required for certain criteria parameters, for example, the roll-back angle required for the IMO IS code Severe wind and rolling (weather) criterion. These calculations may be referenced in certain criteria.

Parent calculations in Maxsurf Stability Criteria dialog

Parent Heeling Arms In most cases a ship is subject to specific heeling moments. Those heeling moment are then used in a number of different criteria. The Maxsurf Stability criteria list contains Parent Heeling Arms that can be copied into a custom criteria folder and then cross-referenced into the stability criteria. Page 210

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The advantage of using cross-referenced Heeling Arms is that a heeling arm is now defined (and edited) in only one place. This ensures that all criteria which use a specific heeling arm use exactly the same heeling arm. Another benefit is that, since the heeling arm is defined in one place, it is only displayed once in the GZ graph and not duplicated for each criterion that uses it. Furthermore some newer heeling arm criteria are only available for cross-referenced heeling arms and a greater variety of heeling arm definitions are available through cross-referencing. Parent Criteria The Parent Criteria group contains all the parent criteria types that are available in Maxsurf Stability. Each parent criterion allows you to perform a specific calculation; these are the fundamental criteria from which criteria for specific codes are derived. Parent criteria are special in that you cannot rename, delete or add criteria to the Parent Criteria group. Also the parent criteria settings cannot be saved, they will always revert to their default values when Maxsurf Stability is restarted. This is because the parent criteria are intended for use as templates from which you can derive your own custom criteria. This is done by dragging the required parent criteria in to the “My custom criteria” group or any other group you create. To distinguish the Parent criteria from your derived criteria, they are displayed in bold text in the Criteria list. Predefined Custom Criteria A number of criteria files containing criteria for specific codes are supplied with Maxsurf Stability. These may be found in the “HMSpecificCriteria” folder. This folder can be found in the Maxsurf root directory: c:\program files\Maxsurf. Most specific criteria are locked; those that are not locked require your ship design data to be input. Also see Working with Criteria Libraries on page 218 Appendix D: Specific Criteriaon page 341. Custom Criteria You can create your own set of criteria in the tree as well. This is explained in the section on Working with Criteria on page 214.

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Types of criteria

There are two fundamental types of criteria: Equilibrium criteria Equilibrium criteria are evaluated after an Equilibrium analysis and refer only to the condition of the vessel in its equilibrium state For example: margin line immersion tests, freeboard measurements, trim angle, metacentric height, etc. This type of criterion is also used by the Floodable Length analysis. Equilibrium criteria can be recognised by the

icon.

Criteria derived from measurements of the GZ curve. These are calculated after a Large Angle Stability analysis and during a Limiting KG analysis. For example, area under GZ curve between specified limits, angle of maximum GZ, etc. These criteria are often referred to as Large Angle Stability (LAS) or GZ criteria. Note that there is some cross-over between the criteria types, notably angle of equilibrium heel. This can be measured from the GZ curve by looking for an up-crossing of the GZ=0 axis. The equilibrium heel angle is also a fundamental output of the Equilibrium analysis. The same also applies for GMt. For this reason, in some criteria sets some criteria are included twice, once in the form of an Equilibrium criterion and again as a Large Angle Stability criterion. For a criterion to be used in the search for maximum VCG in the Limiting KG analysis, it must be a LAS criterion. This is because it is only this type of criteria that is more likely to pass as VCG is reduced. A check is also made to ensure that any selected Equilibrium criteria are passed, but they cannot be included directly in the search algorithm. You will notice that different icons are used to differentiate between different types of criteria. These icons are derived from the parent criterion type. The different types of criteria and their icons are described below: Folder icon, create separate folders to store related criteria. All folders must have unique names (even if the parent folders have different names). Equilibrium criterion. These criteria are evaluated only after an equilibrium analysis has been performed. GZ criterion. These criteria make measurements from the GZ curved obtained from a Large Angle Stability analysis. GZ area criterion GZ criterion with heeling arm GZ area criterion with heeling arm GZ criterion with several heeling arms and their combinations GZ area criterion with several heeling arms and their combinations Combined GZ criterion. These criteria perform several individual tests on the GZ curve. e.g. STIX. Combined GZ heeling arm criterion. These criteria perform several individual tests on the GZ curve including a heeling arm. e.g. Weather criterion. See next: Criteria Procedures

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Chapter 4 Stability Criteria

Criteria Procedures This section describes how to work with the stability criteria dialog.  Starting the Criteria dialog  Resizing the Criteria dialog  Working with Criteria  Editing Criteria  Working with Criteria Libraries Starting the Criteria dialog

The criteria dialog allows you to select which criteria are selected for inclusion in the analysis and change their parameters. To bring up the Criteria dialog, select Criteria from the Analysis menu:

or use the Criteria button,

, in the analysis toolbar:

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The criteria dialog is shown below:

Note: The Floodable Length analysis uses its own set of criteria. The criteria command will bring up the Floodable Length Criteria dialog when the Floodable Length analysis is selected. Resizing the Criteria dialog

The dialog may be resized and a vertical and horizontal slider can be used to resize the width of the Criteria List and the height of the Criterion Details areas. Note that if, in the unlikely event that the dialog items vanish due to resizing the dialog, the dialog size can be reset by holding down the “Shift” key when you open the dialog. This behaviour is the same as all other resizing dialogs. Working with Criteria

In the Concepts section it was explained how the criteria are listed in a tree list. This section explains how to create and customise your own criteria from the Parent Heeling Arms and Criteria provided with Maxsurf Stability. Page 214

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Using the Criteria Tree List

The tree works in much the same way as the file folders in Windows Explorer: 

Click on the “+” sign to expand the folder (or double click on it).



Click on the “-” sign to collapse the group (or double click on it).



Click on an item’s name or icon to select it



Once selected, click again on the on the item’s name to edit its name

Some short-cut keys for the tree list: Tree control smart keys Alt+Keypad * Right Arrow or Alt+Keypad + Left Arrow or Alt+ Keypad Up Arrow Down Arrow Space

Function Recursively expands the current group completely Expands the current group Collapses the current group Move one item up tree Move one item down tree Include criterion for analysis

Criteria Tree Right-click Context Menu

Several options are available by right-clicking on a criterion or criterion group:

Criterion right-click menu

Include for Analysis: Toggle whether the criterion (or all criteria within the group) should be evaluated. Intact: Toggle whether the criterion (or all criteria within the group) should be evaluated for intact conditions. Damage: Toggle whether the criterion (or all criteria within the group) should be evaluated for damaged conditions. Lock: Toggle whether the criterion (or all criteria within the group) are locked. If a criterion is locked, this prevents inadvertent editing of its parameters. Locking is used for criteria belonging to specific codes where the required values are fixed.

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Add Group: Add a new criterion group. Cut: Cut the criterion (or whole criterion group) to the clipboard. This may then be pasted into another location in the tree. Copy: Copy the criterion (or whole criterion group) to the clipboard. This may then be pasted into another location in the tree. Paste: Paste the criterion (or whole criterion group) from the clipboard to the selected location Rename: Renames the criterion or group. This may also be done by selecting the label, then clicking again in the label. Delete: Deletes the criterion or all the criteria and sub-groups within the group. Defining new Custom Criteria and Groups

New custom criteria sets may be created by first creating a new criterion group and then dragging the desired criteria into the criterion group. By holding down the Ctrl button a copy of the criterion being dragged is created (unless it is a parent criterion, in which case a copy will be made regardless of whether the Ctrl key is held down or not). Alternatively use the Copy and Paste functions from the right-click context menu (see above). It is extremely important to ensure that all criteria groups have unique names. If duplicate group names exit, then loading the criteria file may cause unexpected results. As criteria (and new groups) are loaded they are inserted into the first group that is found with a name that matches the name of the group to which the criterion should belong. If there are groups with the same name, all criteria that should be in a group of that name will end up in the first one and none in the second. Moving Criteria

Criteria may be moved from one group to another by dragging them with the left-mousebutton or by using the cut and paste functions in the right-click context menu (see above). Note that if you drag a criterion from the Parent Criteria group a copy will be made and the original will not be deleted. Copying criteria

You can use the Criteria Tree Right-click Context Menu to copy and paste criteria. Alternatively, you can hold down the CTRL-key while moving the criteria you will copy the criteria. Selecting the Criteria for Analysis

Criteria may be selected for analysis by ticking the tick box to the left of the criterion. Other functions are available from a menu activated when the right button is clicked on your mouse. To select an entire group, right-click on the group and choose Include for Analysis from the menu. Editing Criteria

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Criterion details table

To edit the parameters for a specific criterion, click on the criterion’s name in the tree and the criterion’s parameters will be displayed in the table on the right. Edit the parameters as required and then select the next criterion to be edited from the tree, or click the dialog’s Close button. Please note that the criteria are updated as you change their data and that there is no “Cancel” function for this dialog. If in doubt, use the File | Save Criteria command to save a copy of your current criteria selection and data before making any changes in the Criteria dialog. The parameters that may be adjusted have a white background; those which cannot be edited, have a grey background. The values that are required for passing a criterion are in bold. Check Boxes in Criteria Properties Section of Criteria Dialog

There is some subtly different behaviour for the check boxes in the dialog depending on their context. In most cases there will be group of related options used to define a criterion parameter. For example the limits for an upper integration range or the individual criteria to be evaluated for a more complex criterion:

In both of these cases the selection is cumulative and none of the selections are mutually exclusive. However, at least one must be selected.

In other cases, where the items are mutually exclusive, the check boxes act as radio buttons and only one may be selected. This occurs, for example, with the “Value of GMt at” criterion:

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Finally a check box can be used to select whether a specific effect should be included, for example, GZ curve reduction in the wind heeling criteria:

Criterion Pass/Fail Test

There are some subtle differences between the wordings for different criteria. For example one criterion may state “Shall be greater than…”, whereas another may state “Shall not be less than…”. Maxsurf Stability allows you to make this distinction by selecting the required comparison from a combo-box in the criterion row of the details table:

Description Shall be greater than Shall not be less than Shall be less than Shall not be greater than

Symbol > ≥ < ≤

Logical test Greater than Greater than or equal to Less than Less than or equal to

Damage and Intact

Criteria may be defined as intact or damage stability criteria (or both). Intact criteria are only evaluated for the intact case and damage criteria are evaluated when a damage case has been selected (irrespective of whether there are actually any damaged compartments or tanks in the damage case). Criteria that are defined for both are always evaluated. Criteria that have the WoD option selected will only be evaluated if WoD is active and will use the WoD-adjusted GZ curve; if criteria should also be evaluated using the normal (unadjusted) GZ curve, copies of the criteria, without the WoD option selected, should be made. These options may either be set using the right-click menu or by ticking the appropriate boxes in the bottom of the dialog:

Intact and Damage and Water-on-Deck tick-boxes.

Working with Criteria Libraries

It is possible to load and save the criteria. The parent criteria, built into Maxsurf Stability are not saved, only the criteria that you create or import will be saved. Default Criteria Library File

When starting, Maxsurf Stability will try to open the default criteria library file called: “Maxsurf Stability Criteria Library.hcr” from the directory in which the Maxsurf Stability program resides. By default this is c:\program files\Maxsurf\ Maxsurf Stability Criteria Library.hcr. If this file cannot be found, you will be prompted to locate a criteria file:

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You may select an alternative file or click the Cancel button to proceed and be given the default criteria, which consists of the Parent criteria and a “My Custom Criteria” group. The default criteria library will be automatically updated every time the criteria dialog is closed. Even if you loaded an alternative file, updates will be saved in the default criteria library, either overwriting the existing one or creating a new one. Note It is good practise to save the criteria file with the project in the project folder. That way, when at a later stage you need to re-analyse the project, all criteria are still available. See Saving Criteria below. Saving Criteria

It is also possible to save the criteria into a new file. This can be useful when you are defining new custom sets of criteria that you wish to keep separate or when defining criteria sets for different vessels. Choose Save Criteria As from the File menu. This will simply export all the custom criteria (parent criteria are not saved) to the specified file. Further updates will, however, continue to be saved to the default criteria library file that was opened when Maxsurf Stability was first started, so if you want to save any further changes you will have to resave as described above. Importing Criteria and Specific Criteria Files

New criteria may be added to your criteria list by importing them – choose Import Criteria from the File menu. You will then be asked if you wish to keep the existing criteria:

If you choose “Yes” your existing criteria will be kept, if you choose “No”, all existing criteria except the parent criteria will be removed and replaced by those in the file you are opening. The default criteria library will be over-written with the new criteria so if you wish to keep any custom criteria that you may have added to your default criteria library, you must save them in a new file first. Note that when keeping your existing criteria, it is important to ensure that the group names in the file you are importing are not the same as those that already exist. If this does occur, the imported criteria will be found in the original groups, not in the new groups. A number of criteria containing criteria for specific codes are supplied with Maxsurf Stability. These may be found in the “HMSpecificCriteria” folder. You can import several criteria files in one go using Shift, or Ctrl select to select multiple files in the Open Maxsurf Stability Criteria dialog.

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Criteria File Format

The criteria are saved in a Maxsurf Stability criteria file with the extension .hcr. The file is a normal PC text file, which may be edited manually so as to generate custom criteria. The typical format of the file is given in the following file: c:\Program Files\Maxsurf\\HMCriteriaHelp\CriteriaHelp.html. Editing this file will also allow you to add your own help text or associate rich text format help files (rtf) files with your criteria.

Criteria Results After a Large Angle Stability or Equilibrium analysis, criteria are evaluated and the results displayed in the Stability Criteria table in the Results window. Criteria can also be re-evaluated without having to redo the analysis when “Close and Recalculate” is selected in the criteria dialog. This allows you to edit criteria parameters or selected criteria and re-evaluate using the existing analysis results. After calculation the relevant criteria are also added to the Report. Criteria Results Table

The tested criteria are listed one above the other. Intermediate values are displayed. Values that could not be calculated, e.g.: angle of vanishing stability, angle of equilibrium, etc., have n/a in the Actual and/or Value column. This is normally due to an insufficient range of heel angle having been used. Results may be displayed in “Verbose” or “Compact” format (see above). The format for the results table and the report are specified separately. Chose the Display | Data Format command when the Stability Criteria results are displayed:

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Stability criteria results window: compact format

Stability criteria results window: verbose format

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Report and Batch Processing

As noted earlier, only the relevant criteria results are added to the Report and/or Batch file. Criteria that are not relevant, i.e. any criteria that have a “not analysed” result, are not added to the Report (although they are displayed in the Criteria Results table). For example damage criteria during intact analysis or Equilibrium criteria during a Large Angle Stability analysis are not added to the report. Also see Reporting on page 201 Batch Analysis on page 183

Nomenclature This section gives a brief description of the various values that are determined by Maxsurf Stability in the evaluation of criteria. There are two distinct types of criteria: Equilibrium criteria Equilibrium criteria are evaluated after an Equilibrium analysis and refer only to the condition of the vessel in its equilibrium state For example: margin line immersion tests, freeboard measurements, trim angle, metacentric height, etc. This type of criterion is also used by the Floodable Length analysis. Equilibrium criteria can be recognised by the

icon.

Criteria derived from measurements of the GZ curve. These are calculated after a Large Angle Stability analysis and during a Limiting KG analysis. For example, area under GZ curve between specified limits, angle of maximum GZ, etc. These criteria are often referred to as Large Angle Stability (LAS) or GZ criteria. Note: The metacentre is always (even for Large Angle Stability criteria) computed directly from the vessel’s hydrostatic properties (i.e. water-plane inertia and immersed volume) at the specified heel angle and not from the slope of the GZ curve. This gives an accurate result that is not dependent on the heel angles and intervals tested during the analysis. Definitions of GZ curve features

Some typical GZ curves are shown below, the third graph shows the GZ curve with a heeling arm overlayed.

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Typical GZ curve

Unusual GZ curve with double peak

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GZ curve with heeling arm superimposed GZ Definitions

The table below defines how Maxsurf Stability calculates the various features of the GZ curve: Angle of vanishing stability Angle of vanishing stability with heeling arm curve Downflooding angle Equilibrium angle Equilibrium angle with heeling arm curve First peak in GZ curve

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The angle of vanishing stability is the smallest positive angle where the GZ curve crosses the GZ=0 axis with negative slope. The angle of vanishing stability with a given heeling arm is the smallest positive angle where the GZ curve crosses the heel arm curve and where the GZ-Heel Arm curve has negative slope. The downflooding angle is the smallest positive angle at which a downflooding point becomes immersed. The equilibrium angle is the angle closest to zero where the GZ curve crosses the GZ=0 axis with positive slope. The equilibrium angle with a given heeling arm is the angle closest to zero where the GZ curve crosses the heel arm curve where the GZ-Heel Arm curve has positive slope. In some cases, the GZ curve may have multiple peaks; this often occurs if the vessel has a large watertight cabin. The angle of the first peak is the lowest positive angle at which a local maximum in the GZ curve occurs.

Chapter 4 Stability Criteria

GML or GMT

GZ Curve Heeling arm curve

Maximum GZ Maximum GZ above heeling arm curve

Vertical separation of the longitudinal or transverse metacentre and centre of gravity. The location of the metacentre is computed from the water-plane inertia, not the slope of the GZ curve. Note that the centre of gravity used is the upright centre of gravity corrected by the free surface moments of partially filled tanks in their upright condition, rotated to the specified heel (and trim) angle. The curve of vessel righting arm (GZ) plotted against vessel heel angle A curve of heeling lever, which is superimposed on the GZ curve. This is typically used to assess the effects of external heeling moments, which are applied to the vessel. These include the effects of wind, passenger crowding, centripetal effects of tuning, etc. Depending on the moment that they represent, the heeling arm curves will have different shapes. The heeling arms are never allowed to be negative; if the cos function goes negative, the heeling arm is made zero. If the heeling arm has a power of cos greater than zero, the heeling arm is forced to be zero at heel angles greater than 90° and less than -90°. Positive angle at which the value of GZ is a maximum Positive angle at which the value of (GZ - heel arm) is a maximum

Glossary

The table below describes some commonly used terms:



Angle of heel measured from upright.

Deck Slope / maximum slope

The maximum slope of an initially horizontal, flat deck at the resultant vessel heel and trim. i.e. combined effect of heel and trim. Used for some wind heeling criteria, the Gust Ratio is the ratio of the magnitude of the gust wind heeling arm to the steady wind heeling arm. 1998 CODATA recommended value for standard acceleration of gravity A negative heel angle change. Often a roll back angle is measured from some equilibrium position; the resulting heel angle after the roll back has been applied is more negative than the original. Commonly used in wind and weather criteria to account for the action of waves rolling the vessel into the wind. If a criterion uses a roll back angle, it is often necessary to calculate the GZ curve for negative angles of heel.

Gust Ratio g = 9.80665ms-2 Roll back angle

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Chapter 5 Maxsurf Stability Reference This chapter contains brief descriptions of the tools available in Maxsurf Stability:  Windows  Toolbars  Menus

Windows Maxsurf Stability uses a range of graphical, tabular, graph and report windows.  View Window  Loadcase Window  Damage Window  Input Window  Results Window  Graph Window  Report Window Assembly View and Property Sheet

An assembly view has been added to Maxsurf Stability, this makes it easier to control the visibility of individual tanks and surfaces. The Properties sheet can be used to change tank properties of the tank currently selected in the Assembly or design View. View Window

The View window displays the hull, frame of reference, immersed sections of the hull and any compartments, and the centroids of gravity, buoyancy, and flotation. These positions are represented by: cb cg cf K

centre of buoyancy centre of gravity centre of flotation location of keel (K) for KN during KN analysis

You can choose which type of view is displayed by selecting from the Window menu or the View toolbar. The Zoom, Shrink, Pan and Home View commands from the View menu may be used and work in exactly the same way as in Maxsurf. If a Perspective view is shown, you may also use the Pitch, Roll and Yaw indicators to change the angle of view. Please refer to the Maxsurf manual if you are unfamiliar with these functions. You may set the visibility of the various display elements by using the Visibility command from the Display menu. Two sets of visibility flags are maintained, one is used for all analyses other than tank calibration and the other is used for when the tank calibration analysis is selected. Page 227

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If a view window is visible when an analysis is being carried out, it will display the hull shape using the correct heel trim and immersion for the current step of the analysis. After an analysis, the Select View from Data command in the Display menu may be used to move the hull to a selected position from the Results window. The view of the tanks, compartments and non-buoyant volumes can be toggled between an outline view and a view of the sections. Perspective view

In the perspective view, the model may be rendered.

The rendered view also enables tanks and compartments to be more easily visualised, especially when the hull shell is made transparent.

The rendering options are to be found in the Display menu, with further lighting options in the Render toolbar. Please refer to the Maxsurf manual for more information on the different rendering options available in perspective view.

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Note: Fastest performance will be achieved by reducing the amount of redrawing that is required from Maxsurf Stability. For this reason, it is best to turn off sections, and especially waterlines, when performing an analysis. You may then turn them on again after the analysis has completed. For fastest performance, e.g. when running in Batch mode, minimise the Maxsurf Stability window so that no redrawing occurs. Loadcase Window

In the Loadcase window a spreadsheet table of all loads and tanks is displayed.

Using the tabs on the bottom of the window allow you to quickly browse through the different loadcases. Maxsurf Stability allows you to improve the presentation of the Load Case window by adding blank, heading or sub-total lines in the table. For more information see Working with Loadcases on page 43. The columns that are displayed may be selected using the Display | Data Format dialog. Damage Window

The Damage window is used to specify which tanks and compartments are flooded in each damage case. There is always an Intact case, which cannot be edited, this is the default condition. If flooded volumes are required in the intact case they should be defined as non-buoyant volumes.

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Input Window

The Input window contains tables where the additional Maxsurf Stability design data is entered. The tables in the Input window contain the:  Compartment Definition  Sounding Pipes  Key Points  Margin Line Points  Modulus Points  Bulkhead locations

The input window contains tabs on the bottom that allow you to quickly browse through the different input tables. Compartment Definition

This table can be used to define the tanks and compartments in the Maxsurf Stability models. For more information see Modelling Compartments on page 59 in the Analysis Input section. Sounding Pipes

This table is used to define the tank sounding pipes and calibration intervals. Default values are provided but these may be edited if necessary.

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Key Points

There are several types of Key Points:  Down Flooding points  Potential Down flooding points  Embarkation points  Immersion Points

Only downflooding points are used in determining the downflooding angle, which is used in criteria evaluation. Margin Line Points

The margin line is used in a number of the criteria. Maxsurf Stability automatically calculates the position of the margin line 76mm below the deck edge when the hull is first read in. If necessary, the points on the margin line may be edited manually in the Margin Line Points window (the deck edge is automatically updated so that it is kept 76mm above the margin line). Modulus Points

This table is used to define the allowable limits for shear force and bending moment during the longitudinal strength calculations. Bulkheads

See Floodable Length Bulkheads on page 95. Results Window

The Results window contains ten tables, one for each of the different analysis types plus criteria results and key points results tables. When switching mode, the currently selected results table will change to reflect the current analysis mode. Note that results are never invalidated if analysis options are modified – it is up to the user to ensure that the results are recalculated as necessary. Setting the Data Format

It is possible to configure Maxsurf Stability so that only the results that you wish to see are displayed. To do this, choose Data Format from the Display menu.

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A dialog similar to the one above will appear. Items that are selected with a tick will be displayed in the Results window and on any printed output. Items that are not selected are still calculated during the analysis cycle, but are not displayed. You may change the display format at any time after the analysis without having to redo the calculations. The data available for display depends on the analysis. Data Layout

Most analysis data can be formatted vertically or horizontally to fit better on the screen or the printed page. For example, with Upright Hydrostatics, the data can be formatted so that each draft has a column of results, or so that each draft is on a separate row.

To change the format, select Data Format from the Display menu, and select either the horizontal or vertical layout button. Key Points Data Result Window

Key points data is calculated for Large Angle Stability, Equilibrium and Specified condition Analysis. The DF angle column is only visible when the analysis mode is set to Large Angle Stability and the Freeboard column is only displayed when the analysis mode is set to Equilibrium or Specified condition. Page 232

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Stability Criteria Result Window

If stability criteria are turned on in the analysis menu, they will be evaluated during Large Angle Stability, Limiting KG and Equilibrium analyses. The results of the criteria evaluation are presented in this table after Large Angle Stability and Equilibrium analyses. Criteria results are not displayed in this table after a Limiting KG analysis. The results may be displayed in compact format:

Alternatively, the results can be displayed in verbose format, where all the intermediate calculations are shown, by selecting the desired format in the Display | Data format dialog.

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Compartments Result Window

It is possible to view the flooded volume and centre of damaged compartments and nonbuoyant volumes. This is currently enabled for the following analyse: Upright Hydrostatics; Large Angle Stability; Equilibrium and Specified Condition analyses and Tank calibration. Where applicable, you can chose the condition to be displayed with the pull-down menus in the Results toolbar (or the Display|Select View from Data menu command -- though this is less convenient). For instance you can use this to see the different lost buoyancy at each draft of an Upright Hydrostatics analysis or at each heel angle for a Large Angle Stability analysis. The lost buoyancy of damaged tanks and compartments and non-buoyant volumes is given (intact tanks and compartments show “n/a”). For linked tanks and compartments the result for each component is also given.

New “Compartments” table in Results window

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Water on Deck volumes

In the case of Large Angle Stability analysis with water on deck, additional columns will be shown which display the additional volume of water on deck in each WoD compartment (as selected in the current Damage case). Graph Window

The Graph window displays graphs, which show the results of the current analysis. Maxsurf Stability will automatically display the graph that displays the result of the current analysis when you select Graph from the Windows menu or press the toolbar button. Alternatively you can select a specific graph using the Windows | Graphs menu item. Only the graphs that are applicable to the current analysis can be displayed. Graphs can be copied using the Edit | Copy command. And may also be exported to DXF from the File | Export menu Depending on the analysis mode, different graphs are available. Upright Hydrostatics Analysis:  Hydrostatics  Curves of Form  Curve of areas – different graph for each draft tested (selected using Display|Select view from data)

Large angle stability Analysis  Righting Lever (GZ)  Curve of areas – different graph for each heel angle tested (selected using Display|Select view from data)

 Max steady heel angle  Large angle stability (hydrostatic data other than GZ)  Curves of Form  Dynamic stability (GZ area)

Equilibrium Analysis:  Curve of areas

Specified condition Analysis:  Curve of areas

KN Values Analysis:  Cross curves (KN)

Limiting KG Analysis:  Limiting KG

Floodable length Analysis:  Floodable length

Longitudinal strength Analysis:  Longitudinal strength  Curve of areas

Tank Calibration  One graph for each tank

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For many graphs you can select what is plotted and other options with the Display | Data Format dialog. Graph type

Maxsurf Stability can graph many types of data depending on the type of analysis being performed. These graphs include Upright Hydrostatics, Curves of Form, Curve of Areas, Righting Lever (GZ curve), Longitudinal Strength, Floodable Length and Tank Capacities. These can all be displayed via the Graphs item in the Windows menu. Tip: You can use the Select View from Analysis Data option (page 204) to see the Curve of Areas for each heel angle and/or intermediate stage during the analysis. Interpolating Graph Data

To display an interpolated value from one of the curves, use the mouse to click anywhere on the curve. The data in the lower left corner of the window will change to display the curve name and co-ordinates of the mouse on the curve. Click anywhere on the dashed line and drag it with the mouse; as you move the cursor the interpolated values will be displayed.

Note: In case multiple curves are plotted in the same graph you can switch between the curves by clicking on them. Maxsurf Stability will ignore the exact position you click on the curve to allow reading all related interpolated values along the black dashed line. GZ Graph

The GZ value, Area and corresponding heel angle can be measured by using the slider; the slider data is displayed at the bottom of the Graph window. The area is integrated from zero heel angle to the location of the graph slider.

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Note: Because the horizontal axis scale is always in degrees, the area is always given in units of length.degrees and cannot be displayed in units of length.radians.

Note The lower integration limit is always zero (irrespective of the equilibrium angle). Thus if you require the area between two limits, you must subtract the area at the lower limit from the area at the higher limit. Curve fitting for GZ graph

A curve fit will be performed if all the heel angle intervals are less than or equal to 10˚. If this is the case, a parametric cubic spline is used to fit a smooth curve through the calculated GZ data at the specified heel angles. This ensures that the fitted line goes exactly through the calculated GZ points. If you wish to prevent this curve fitting, add a heel angle interval of greater than 10˚ as the final step. This can sometimes be useful if you expect a discontinuity in the GZ curve. Graph data

The graphed data can be obtained by double clicking on the graph. Since the graph data contains more data points than most tables in the results window, this double click can be extremely helpful to export the analysis data to for example Excel fro further processing. Especially in the case of the sectional area curve, where there is no tabular data available. Also see: Copying Tables on page 203. Graph Formatting

When you are in the Graph window you can use the View | Colours and lines dialog to change the colours of the curves in the graph as well as the background. The View | Font command allows you to change the text size and font size.

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Copying Graphs

You can copy the contents of the Graph window using the Copy command or Ctrl+C. Note that the picture is placed in the clipboard as a meta-file which can be resized in Word or Excel. Note When the graph is pasted in Microsoft Word®, the graph can be edited by right clicking on the graph and selecting “edit picture”. Graph grid, annotations and labels

The right-click pop-up menu in the Graph view now allows graph labels and annotations to be turned off:

Visibility of graph labels and annotations can be toggled

A Graph options dialog has been added, this allows some control over the number of gridlines displayed (Right-click | Graph options):

Gridline density can be controlled

Furthermore, “Show Legend” has become a single toggle menu item, rather than two separate menu items.

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Report Window

Note It is recommended that you use the option to report directly to Microsoft Word unless you have a very good reason not to. Maxsurf Stability contains a Report window. This window is used to create a progressive summary of the analyses that have been carried out. This report can be edited via Cut, Copy and Paste; printed, saved to and recalled from a disk file. Report Window Page Setup

When you are in the Report window, the File | Page setup command allows you to customise the page orientation and size you wish to use for reporting. This is important because, inserted tables will be automatically formatted to fit the current page set up. However, once the tables have been placed into the report, their formatting will not be changed by changes to the print set up. Hence it is often most convenient to select the desired report page set up before any analyses have been made. You can for example choose the landscape Page Setup prior to running an analysis to make the tables fit better. Maxsurf Stability will split most results tables so they fit the specified page set up. However, both Loadcase and Criteria results tables will not be split. Editing a Report

The Report window has it’s own toolbar permanently attached to the view, as well as a ruler showing you tab stops, indentation and margin widths. Underneath all of this you have your actual editing area. As the built-in report window only has basic editing and formatting functionality, it is recommended that the report window be used only to accumulate the results. Once all the results have been gathered in the report window, these should be saved and opened in a word processor such as Microsoft Word or Open Office for formatting:  set the results tables up as you want them to appear in the report (the report uses the same column widths, fonts etc.); do the same for the graph widow;

 choose an appropriate paper size for the report (the tables will be split to fit this paper size, so choosing a wide paper size will prevent all but the widest tables from being split);

 copy and paste the Maxsurf Stability report into Microsoft word. Use the Format | Autoformat function in Word (with the default settings) to set the correct styles for the different levels of heading in the document, this will facilitate generating a table of contents and also allows you to re-format the various styles (or import a custom set of styles using the style organiser in Word).

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The information below is provided for reference, but it is strongly recommended not to use any of the formatting commands in the Report window. The toolbar has a number of buttons that allow you to change either the current settings, or the section of text that is currently highlighted. The toolbar contains the following items: Font combo box Font Size combo box Bold Italic Underline Colour Left Justify Centre Justify Right Justify Bullet

Use this to change the current font Use this to change the current font size Use this to toggle the Bold style Use this to toggle the Italic style Use this to toggle the Underline style Use this to set Text Colour Use this to set Left Justification Use this to set Centre Justification Use this to set Right Justification Use this to toggle Bullet Points

The Ruler comes in two formats, in metric and in inches - the format you have displayed on your screen depends on the current Dimension Units you have (use Units in the Display menu to change this). The format shown below is metric.

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The Ruler allows you to set left, right, centre, and decimal tab stops. The tab stops are very useful for creating columns and tables. A paragraph can have as many as 20 tab positions. The ‘left’ tab stop indicates where the text following the tab character will start. To create a left tab stop, click the left mouse button at the specified location on the ruler. The left tab stop is indicated on the ruler by an arrow with a tail toward the right. The ‘right’ tab stop aligns the text at the current tab stop such that the text ends at the tab marker. To create a right tab stop, click the right mouse button at the specified location on the ruler. The right tab stop is indicated on the ruler by an arrow with a tail toward the left. The ‘centre’ tab stop centres the text at the current tab position. To create a centre tab stop, hold the shift key and click the left mouse button at the specified location on the ruler. The centre tab stop is indicated on the ruler by a straight arrow. The ‘decimal’ tab stop aligns the text at the decimal point. To create a decimal tab stop, hold the shift key and click the right mouse button at the specified location on the ruler. The decimal tab stop is indicated on the ruler by a dot under a straight arrow. To move a tab position using the mouse, simply click the left mouse button on the tab symbol on the ruler. While the mouse button is depressed, drag the tab to the desired location and release the mouse button. To clear a tab position, simply click on the desired tab marker and drag it off the ruler. Normally, a tab command is applicable to every line of the current paragraph. However, if you highlight a block of text before initiating a tab command, the tab command is then applicable to all the lines in the highlighted block of text. Keyboard Support for Reports

In addition to menu support, there are also several useful keystrokes that are available while editing the report. These are listed below for convenience: Ctrl+B Toggle Bold on/off Ctrl+U Toggle Underline on/off Ctrl+PageUp Ctrl+PageDown

Position at the top of the report Position at the bottom of the report

Ctrl+Enter

Insert a page break

Opening and Saving the Report

The report can be saved to a file or read in from a file using the Save and Open Menu commands with the report window highlighted. This is useful if you wish to append an analysis to a report that had been calculated at some time in the past. (Load in the old report, perform the analyses; the new results will be appended to the end of the report which may then be resaved).

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Pasting images into the report

Sometimes, it is desirable to insert schematic images of the vessel into the report. This is very easily done, by copying an image from one of the design views and then pasting it into the report at the desired location. The image copied is as per the image displayed in the Maxsurf Stability view window. Ensure that the colors selected will be easily visible in the white background of the report view. Depending on which Microsoft operating system you are using (notably Win98), the image may not maintain its aspect ratio and may be pasted into the report as a square. To overcome this problem, paste the image into Microsoft Word first, then copy it from Word back into the Maxsurf Stability report window.

Toolbars Maxsurf Stability has a number of icons arranged in toolbars to speed up access to some commonly used functions. You can hold your mouse over an icon to reveal a pop-up tip of what the icon does.

File Toolbar

The File toolbar contains icons that execute the following commands: New – Open – Save – Cut – Copy – Paste – Print Edit Toolbar

The Edit toolbar contains icons that execute the following commands: Add Row - Delete Row | Sort Loadcase Rows – Move Loadcase/Tank Row up – Move Loadcase/Tank Row Down View Toolbar

The View toolbar contains icons that execute the following commands: Zoom – Shrink – Pan – Home View – Rotate – Assembly window.

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The Rotate command is only available in the Perspective window. The Assembly window is not available in Maxsurf Stability. Analysis Toolbar

The Analysis toolbar contains icons for selecting the current analysis, loadcase and damage case: Analysis Type – Current Loadcase – Current Damage Case

The Analysis toolbar also contains icons that execute the following commands: Criteria (dialog) | Start Analysis – Pause Analysis – Resume Analysis | Update Tank Values in Loadcase The “Update Tank Values in Loadcase” is exactly the same as the menu command for “Recalculate Tanks and Compartments on page 254. Window Toolbar

Allows quick switching between commonly used windows: Perspective – Plan – Profile – Body Plan | Loadcase – Damage Case | Compartment – Downflooding – Margin Line – Modulus – Bulkheads | Results for Current Analysis – Criteria Results – Key Point Results | Graph – Report Design Grid Toolbar

The Design Grid toolbar contains icons that show or hide various items in the graphical views Frame of Reference (always on) | Toggle Design Grid Visibility Design Grid | Design Grid Labels | Design Grid Tickmarks Visibility Toolbar

The Visibility toolbar contains icons that show or hide various items in the graphical views: Sections – Datum Waterline – Waterlines | Key Points – Margin Line | Loadcase mass items | Tanks – Damaged Tanks – Compartments – Damaged Compart. – Linked Negative Compartment. – NBV – Tank Names – Tank Fluid Level – Tank Sections – Tank Outlines | Probabilistic Damage Zones * NBV = Non Buoyant Volume

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Edge VIsibility Toolbar

The Visibility toolbar contains icons that show or hide various items in the graphical views: Hull Surface Edges – Internal Surface Edges – Feature Edges – Bonded Edges Render Toolbar

Render – Render transparent – Toggle custom light 1 – Toggle custom light 2 – Toggle custom light 3 – Toggle custom light 4 – Customise light settings

Report Toolbar

Spool results to report View (extended) Toolbar

Set Home View – Colour – Font – Preferences – Properties Design Grid Toolbar

Display Frame of Reference (always on) – Display Design Grid – Show Grid – Show Labels – Show Ticks Extra Buttons Toolbar

Add surface areas to loadcase – Preferences | Heel – Trim – Draft – Displacement – Displacement – Specified Condition – Permiability – Fluid simulation – Densities – Waveform – Grounding – Batch Analysis Data Format – Units – Coefficients – Set to DWL – Set View from Data –Visibility Dialog – Show Single Section

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This toolbar provides a number of buttons for commonly used commands in case you should wish to customise your toolbars.

Menus The following section describes all of the menu commands available in the Maxsurf Stability program.  File Menu  Edit Menu  View Menu  Case Menu  Analysis Menu  Display Menu  Data Menu  Window Menu  Help Menu File Menu

The File menu contains commands for opening and saving files and printing. New

Creates a new table for whichever input table is frontmost, e.g: when the Loadcase Condition is the frontmost window, the New command will create a new loading condition. When the Compartment Definition table is frontmost, New creates a new compartment definition. Open

When no design is open, selecting the Open command will show a dialog box with a list of available Maxsurf designs. Select the design you wish to open, click the Open button. The requested design will be read in and its hull shape calculated for use in Maxsurf Stability. If a design is already open, the Open command will open whichever file corresponds to the frontmost input window. Close

The Close command will delete the data in the frontmost window. Maxsurf Stability will ask whether you wish to save any changes. Selecting Close when one of the design view windows is frontmost will close the current Maxsurf design. Save

Selecting Save will save the contents of the frontmost window to a file on the disk. Save As

Selecting Save As performs the same function as save but allows you to specify a new filename preventing the original file from being overwritten.

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Import

Allows import of file types other than Maxsurf design files nuShallo Allows direct import of a nuShallo pan file. GHS Allows direct import of a GHS geometry file. A full GHS model file may be imported directly into Maxsurf Stability for analysis. Because the GHS file does not contain a full, interconneceted, three-dimensional model of the hull, the geometry is locked: the tank geometry is locked and tanks cannot be added to the model. The full model including critical points, tanks and sounding pipes are read from the GHS file. The following limitations currently apply, but will be removed in subsequent versions:  Maxsurf Stability supports only a single buoyant hull part. The buoyant hull part with the most sections is loaded from the GHS file.

 Linked negative tanks are not supported in Maxsurf Stability. Any container parts with elements with negative effectiveness will be read in as tanks. All other cotainers are read in as tanks.

 Sail parts are ignored

Import DXF Background Enables you to import a DXF file into Maxsurf Stability to use as construction lines. The DXF file will be displayed in the design views. Import Image Background Enables you to import an image file (jpg, gif, bmp or png) file into the background of any of the Maxsurf Stability design views. Export

Selecting Export enables you to export a Maxsurf Stability file as a variety of different file formats such as: DXF or IGES DXF exports sections as closed poly-lines. In addition, each tank, compartment and non-buoyant volume is exported on a separate layer (the layer name being the same as the compartment name, so it is important to have unique compartment names). IGES exports the NURB surface data. See the Maxsurf manual for more information. GHS If you have a Hydrolink license, you may export the Maxsurf Stability model to a GHS geometry file. The hull, tanks and compartments and key points are all exported. To enable the export command, chose Edit | Activate GHS export.

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Chapter 5 Hydromax Reference  Maxsurf Stability supports only a single buoyant hull part with one byouant component. The buoyant hull is exported as a single part with a single buoyant component (Non-buoyant volumes are included in this part as components with negative effectiveness). It is possible that this might cause problems for some models where the section through the hull at a certain location contains more than one closed contour. In subsequent versions of Maxsurf Stability we will add the capability to divide the main buoyant hull into different components.

Maxsurf Stability v8.0 file Also allows users to export Maxsurf Stability files that are compatible with earlier versions of Maxsurf Stability. Export Bitmap Allows you to export the rendered image as a bitmap file at the specified resolution. This command is only available when the Perspective window is frontmost with rendering turned on. Fredyn Maxsurf Stability is able to export data suitable for input into Fredyn, exporting Maxsurf Stability calibration results, hull form and compartment definitions into Fredyn input files. To export use the File|Export|Fredyn… command. The Export will generate 3 files, all with the name you specify in the “Fredyn Export XML” dialog. The following files will be generated .xml: Containing compartment definition .out: Tank calibration results and compartment definitions .txt: Mesh file representing the current hull shape. Before doing the Fredyn export ensure you have specified the desired trim and heel ranges, and performed a tank calibration, as this information is required for the export. Fredyn mesh group definition When exporting from Maxsurf Stability to Fredyn you will be asked to name the .xml file and also the location to which it should be saved. After assigning the .xml file name, the following dialog will appear:

“Fredyn group definition” dialog

This dialog is where the user will specify the values for the variables used to generate the mesh file that defines the geometry of the hull. The most important part of the procedure is setting up the groups required in the mesh file. The groups are defined by selecting the surfaces to be measured and defining a boundary box that defines the limiting extents of the group. Contours will be formed through the selected surfaces and then trimmed back to the bounding box.

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In the group definition dialog, any number of groups may be added and for each group. For more information on each of the fields in the table click on the Help button on the right hand side of the dialog. Allows you to export the rendered image as a bitmap file at the specified Import Main Criteria

Imports criteria from the selected criteria files. Current criteria may be kept or discarded. Save Main Criteria As

Exports the current criteria set to the specified file. It is good practice to save the criteria library with each project in a project folder. Note that a branch of the criteria tree may be saved in its own file by right-clicking on the branch folder in the Criteria dialog tree. The whole library may be saved by right clicking on the root “Criteria” branch; this is not normally necessary as this is done after any major changes to the criteria definition. Import Prob Damage Criteria

As for main criteria but applies to the probabilistic damage criteria. Save Prob Damage Criteria As

As for main criteria but applies to the probabilistic damage criteria. Rest Prob Damage Criteria to defaults

Results the probabilistic damage criteria to their default values. Load Densities

Loads density table data previously saved from Maxsurf Stability – can be useful for synchronising the densities on several computers. Save Densities As

Saves the Fluid densities table data, see Density of Fluids on page 195. Page Setup

The Page Setup dialog allows you to change page size and orientation for printing. Print

The Print command allows you to print the contents of the frontmost window on the screen. Exit

Exit will close Maxsurf Stability and all the data windows. If you have any data or results, which have not been saved to disk, Maxsurf Stability will ask you if you wish to save them before quitting. Edit Menu

The Edit menu contains commands for working with tables. Undo

Undo may be used with desk accessories, but cannot be used on Maxsurf Stability drawing windows or data windows.

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Cut

Cut may be used in the Report window but cannot be used on Maxsurf Stability drawing or data windows. Copy

The Copy command allows you to copy data from any of the windows, including the design view, input tables, results tables and graph window. Paste

Choose the Paste command to Paste data into the Loadcase window or other input tables, or the Report window. Paste cannot be used in the View, Graph or Results windows. Select All

Selects the entire Report. Fill Down

Copies text in a table down a column like a spreadsheet. Table

Performs operations on Maxsurf Stability’s Report window. Insert New Table Create a new table in the Report. Insert Row Insert a new row into the current table in the Report. Split Cell Split the currently selected cell into two separate cells in a table in the Report. Merge Cells Merge the selected cells in a table into a single cell in the Report. Delete Cells Delete current cell, column or row or a range of cells, columns or rows in the Report. Row Positioning Set Justification for the current table row or an entire table in the Report. Cell Border Set Cell Border Width for a single cell or range of cells in the Report. Cell Shading Set Cell Shading Percentage for a single cell or a range of cells in the Report. Show Grid Toggle table grid lines in the Report. Add

The Add command is used to add an entry to the input tables (Load, tank, margin line point etc.). Delete

The Delete command will delete rows from the input tables. If no rows are selected, the last row in the window will be deleted, otherwise all selected rows will be deleted.

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Sort Items

Sorts the selected rows in the Loadcase window

Move Items Up

Moves the selected rows up (if possible) in the Loadcase and Compartment definition tables. Move Items Down

Moves the selected rows down (if possible) in the Loadcase and Compartment definition tables. Add Surface Areas

This command automatically adds the surface areas and centres of gravity of all hull surfaces into the current loading condition. This is useful for estimating the initial weight of hull plating. Activate / Deactivate GHS Export

This command activates the GHS Import command in the File menu if a Hydrolink License is available. It can also be used to release the Hydrolink license – a restart of Maxsurf Stability will be required for this to take effect. Preferences

The Maxsurf Stability preferences dialog allows you to set your analysis tolerances (or: error values) and select the option to stream the report to a Microsoft Word document. Also see: Tolerances on page 190 Streaming results to Word on page 201. View Menu

The View menu contains commands for controlling the views in the graphics windows. Zoom

The Zoom function allows you to examine the contents of the design view windows in detail by enlarging the selected area to fill the screen. Shrink

Choosing Shrink will reduce the size of the displayed image in the design view windows by a factor of two. Pan

Choosing Pan allows you to move the image around within the View window. Home View

Choosing Home View will set the image back to its Home View size.

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Rotate

Activates the Rotate command, which is a virtual trackball which lets you freely rotate a design in the Perspective view window. Set Home View

Choosing Set Home View allows you to set the Home View in the View window. To set the Home View, use Zoom, Shrink, and Pan to arrange the view, then select Set Home View from the View menu. Colours and lines

The Colours and lines function allows you to set the colour and thickness of the lines, labels, and graphs. Remember to always be careful when using colour. It is very easy to get carried away with bright colours and end up with a garish display that is uncomfortable to work with. In general it is best to use a neutral background such as mid grey or dull blue and use lighter or darker shades of a colour rather than fully saturated hues. From the scrollable list, select the item whose colour you wish to change. The item’s current colour will be displayed on the left of the dialog. To change the colour click in the box and select a new colour from the palette. To Change the thickness select the thickness from the drop down list. When Loadcase window is frontmost, Colours for the loadcase items can be set. See Loadcase Colour Formatting on page 49. Font

Font command allows you to set the size and style of text.

The text style chosen will affect the display and printing of all text in the Report, Loadcase, Graph, Curve of Areas, and Results windows. Toolbar

Allows you to turn the Toolbars on and off. Status Bar

Allows you to turn the Status Bar on and off at the bottom of the screen.

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Assembly

Show or hide the assembly tree view. Properties

Displays the properties sheet, which may be used to view parameters of selected objects (such as tanks).

Full Screen

Maximises screen usage. Case Menu

Commands associated with the Loadcases and Damage cases Edit Loadcase

Edit the properties of the current Loadcase (name and whether it is a loadcase or Loadgroup). Loadcases are created, opened and closed through the file menu. See Working with Loadcases on page 43. Add Damage case

Add another damage case Delete Damage case

Delete the selected damage cases Edit Damage case

Edit the properties of the selected damage case Extent of Damage

Automatically finds the breached tanks and compartments due to a cuboid extent of damage (or in the case of Probabilisitic damage, the zone or sub-zone). Create cases from Zone Damage

Automatically creates damage cases based on the zones that have been defined for Probabilistic damage analysis. (This is only required if you want to manually recreate some or all of the Proabilistic damage analysis conditions; when running Probabilistic damage analysis, temporary damage conditionas are created automatically.) Max. number of Loadcases

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Analysis Menu

The Analysis menu can be used to change the current analysis mode. It also contains commands to set the input data and analysis settings and environment options required for the current analysis. Note: It is good practice when preparing to run analysis to work down the Analysis menu starting at the top and checking all of the settings and environment options. Heel

Selecting Heel allows you to specify the three ranges of heel angles that you wish Maxsurf Stability to step through. Separate ranges are used for Large Angle Stability, KN and Limiting KG analyses. Trim

Allows the specification of the trimming mode to be used for the analysis. This can be fixed trim; free-to-trim to loadcase; free-to-trim specifying initial trim value and free-totrim specifying LCG position. Draft

The range of drafts used for the analysis of upright hydrostatics can be set using this command. KG for the upright hydrostatics is also specified in this dialog. Displacement

The range of displacements used for the analysis of KN values, Limiting KG and Floodable Length can be set using this command. The vertical centre of gravity to be used for KN and Floodable Length analyses is specified here. Permeability

The range of permeabilities used for the Floodable Length analysis are set using this command. Calibration Options

Specify whether compartments and non-buoyant volumes should also be calibrated. MARPOL Options

Select MARPOL Regulation and specify which tanks should be incuded in the MARPOL oil outflow analysis. Specified Condition

Allows you to specify Heel, Trim, CG, Displacement and Draft for the Specified Condition analysis. Fluids

Allows you to specify whether to use Corrected VCG method or Simulate Fluid Movement method when treating the fluid contained in slack tanks. See Fluids Analysis Methods on page 193. Density

This command allows you to set the density of fluids used in the analysis. See Density on page 195.

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Waveform

The Waveform command allows you to perform analysis for a flat waterplane or sinusoidal or trochoidal waveforms. Criteria

The criteria menu item will bring up the criteria dialog. This allows you to specify which criteria will be checked during the analysis. See Criteria on page 209. When the floodable length analysis is selected, the criteria command will bring up a Floodable Length Criteria dialog with criteria that only apply to floodable length analysis. Grounding

Specifies grounding on one or two points of variable length for use with the Equilibrium and Longitudinal Strength analyses. Update Loadcase

Checks for changed tanks and makes sure that any tanks and compartments that have not been formed are correctly calculated. It then updates the loadcase with the correct capacities and free surface moments for the tanks. Also recalculates totals and subsubtotals after a row sorting or moving command. Also see: Tank Loads on page 51 Recalculate Tanks and Compartments

Forces all tanks and compartments to be re-formed from their initial definition. This command also updates the loadcase. If any of the tank boundaries are made up from boundary surfaces, it is better to use “Recalculate Hull Sections” after re-opening the Maxsurf model to make sure the latest internal structure surfaces are being used as well. Recalculate Hull Sections

Deletes all existing hull, tank and compartment sections and recalculates them from the hull surface data and compartment definition. This is particularly useful if the underlying Maxsurf model has been modified, if you wish to recalculate at a different precision, or if you wish to modify whether skin thickness or trimming options are applied. Note: To be able to update the Maxsurf Stability model to changes made in Maxsurf see Updating the Maxsurf Stability Model on page 30 for a stepby-step procedure you can follow. Snap Margin Line to Hull

Project all of the margin line points horizontally onto the hull surface, ensuring that the margin line follows the hull shape precisely. Also see: Margin Line Points on page 95.

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Set Analysis Type

Choose the analysis type you wish to use from the sub-menu. Start Analysis

Selecting Start Analysis causes Maxsurf Stability to start performing the specified analysis. The analysis may be halted at any time by choosing Stop Analysis from this menu, also. Resume Analysis

If you have halted analysis by choosing Stop Analysis, Resume Analysis may be used to restart the calculation from the point where it was interrupted. Stop Analysis

This command halts the analysis at the current iteration. Note that the analysis may not have been completed and in the case of large angle stability, equilibrium condition and KN values, any data displayed for the final iteration may be incorrect. Start Batch Analysis

Maxsurf Stability will run the selected analyses for all combinations of load and damage cases using the batch processing command. Results are written to a tab delimited text file as specified by the user at the start of the analysis. Spool to Report

Send the results of the analysis to the report upon completion. This should be turned on before commencing the analysis to ensure that results are added to the report when the analysis is completed. Display Menu

The Display menu contains commands for controlling the data, which are displayed in the graphics and other windows. Data Format

Data Format allows you to choose which data are tabulated and graphed (Upright Hydrostatics, Stability, Equilibrium and Specified Condition). A dialog box allows you to choose from a range of stability variables. See Setting the Data Format on page 231.

Hydrostatic results Data format dialog

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Used to select display options for Criteria results:

Criteria table Data format dialog

Used to select which columns are displayed in the Loadcase window:

Loadcase Data format dialog

When the Max. Safe heeling angle angles graph is shown as a result of a Large Angle Stability analysis the Data Format dialog may be used to customise the graph layout:

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Max safe heeling angle Data format dialog

May be used to customise the Floodable length graph:

Floodable length Data format dialog Set Vessel to DWL

Rotates the vessel back to upright and to DWL after an analysis has been completed (or Select View from Data used). This is required for automatic update of the Loadcase (note that if you do not rotate back to the DWL, the Loadcase will not update while editing – only when start another analysis). This is to ensure that tank data in the Loadacase are for the vessel in the upright condition, not for tanks with the vessel at the final heel and trim of the last analysis. Select View from Data

This function may be used to synchronise the display in the Design View window with one of the sets of data in Results window. The view may be set from any of the results from Upright Hydrostatics, Large Angle Stability or Equilibrium analyses. Simply highlight the column or row that corresponds to the condition you wish to view and select “Select View From Data”; the Design View will change to match the condition in the selected row or column in the Results window. Visibility

The visibility of tanks, compartments, labels, hull contours, and other items in the design view may be set by using this dialog. Prob damage zones

Toggle the visibility of the probabilistic damage zones.

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Individual Loadcase masses

Toggle the visibility of the individual mass items in the current loadcase. Background

Controls whether the background DXF construction lines and the background images are displayed or not. The background may be loaded from an existing DXF file using the Import function in the File menu. Tools for positioning and scaling the background image are also here. The commands in the submenu are only available when a background image or DXF has been imported. See the Maxsurf manual for more details Hide DXF Hides the DXF background. Show DXF Shows the DXF background. Delete DXF background Deletes the DXF background. Hide Image Hides the background image in the current view window. Show Image Shows the image in the current view window. Set Image Zero Point Sets the image zero point. This command is not available for images in the perspective window. Set Image Reference Point Sets the image reference point.. Delete Image Deletes the background image in the current view window. Design Grid

The grid submenu allows you to hide the grid or show the grid with or without station grid labels. The grid can only be displayed when the vessel is in upright position on its design waterline. The option to display the grid will be greyed out when the ship is currently displayed in, for example, a trimmed state at the end of an equilibrium analysis. Switching analysis type puts the boat back into upright position on its design waterline. Show Single Hull Section in Body Plan

Selecting the Show Single Hull Section item from the Display menu will change the display in the Body Plan window to show only one section through the hull, as well as a control box, similar to the one in Maxsurf, in the top right corner of the window. The section being displayed can be chosen by clicking on the section indicators at the top of the control box. Alternatively, the section chosen can be changed by pressing the left or right cursor keys on your keyboard. This allows you to rapidly step through the hull sections from bow to stern. Also see: Show Single Hull Section on page 35

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Render

When the Perspective window is the current view for the model the Render option may be toggled on and off to render the surfaces. Render Transparent

When the Perspective window is the current view for the model the Render Transparent option may be toggled on and off. Render Transparent makes the hull surfaces of the model semi transparent so that the rendered tanks and compartments within the model may be viewed. Animate

This command is available for any analysis that steps through several steps. For example, when a waveform has been specified and an equilibrium analysis is selected or after a Large Angle Stability analysis over a heeling range. Selecting Animate will animate the stability sequence in the design View window, through the range of heel angles specified. You may set the initial viewing position in the Perspective View window using the Pitch, Roll and Yaw indicators. When Maxsurf Stability has finished calculating the frames the sequence may be replayed by moving the mouse from side to side. Clicking the mouse button will terminate the animation. If animation is chosen after an Equilibrium Analysis has been performed in waves, the animation will automatically cycle through the full range of wave phases, giving a simple visual simulation of the motion of the hull through the wave. Hold the shift key down while selecting the command to save the animation. Data Menu Units

The units used may be specified using the Units command. In addition to the length and mass units classes, units for speed (used in wind heeling and heeling due to high-speed turn etc. criteria) and the angular units to be used for areas under GZ curves, may also be set. The angular units for measuring heel and trim angles are always degrees. See Setting Units on page 43 for more information. Coefficients

Allows you to customise how you wish to calculate the coefficients as well as the display format for the LCB and LCF. See Customising Coefficients on page 42 for more information. Design Grid

Access to the Design Grid is intended for information only. You are not expected to change the Design Grid in Maxsurf Stability. Frame of Reference

Access to the Frame of Reference is intended for information only. You are not expected to change the Frame of Reference in Maxsurf Stability.

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If the position(s) of the Baseline and/or Perpendiculars need to be changed from those defined in the Maxsurf model, they may be changed using the Frame of Reference command. It is highly recommended that the correct frame of reference be set in Maxsurf prior to loading the design into Maxsurf Stability. This will ensure that a consistent frame of reference is used in all the programs. See: Setting the Frame of Reference on page 18. Windage Surfaces

Lets you specify the surfaces that define the windage and underwater profiles of the vessel. Draft Marks

Lets you specify custom draft marks at any position on the vessel. Window Menu

For the items in this menu, each represents a Maxsurf Stability window. Selecting the item brings the appropriate window to the front. Cascade

Displays all the Windows behind the active Windows. Tile Horizontal

Layout all visible windows across the screen. Tile Vertical

Layout all visible windows down the screen. Arrange Icons

Rearranges the icons of any iconised window so that they are collected together at the bottom of the Maxsurf program window. View Direction

Select the desired view direction from the sub-menu. The selected design window will then be brought to the front. Loadcase

Brings the Loadcase window to the front. The Loadcase window allows you to enter a series of component weights, together with their longitudinal and vertical distances from the zero point. These inputs are used to calculate the total Displacement and Centre of Gravity for Stability, KN and Equilibrium analysis. Input

Choose from the Input item to bring the desired Input window to the front and display the Compartment Definition, Key Points, Margin Line Points or Modulus table. Results

Choose from the Results item to bring the desired Results window to the front and display the desired table. Graph

Brings the selected Graph window to the front. The Graph window displays a number of different graphs, depending on which analysis mode is currently active.

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Help Menu

Provides access to Maxsurf Stability Help. Maxsurf Stability Help

Invokes Maxsurf Stability Help. Maxsurf Stability Automation Reference

Invokes the Automation Reference help system. Online Support

Provides access to a wide range of support resources available on the internet. Check for Updates

Provides access to our website with the most recent version listed. About Maxsurf Stability

Displays information about the current version of Maxsurf Stability you are using.

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Appendix A

Appendix A: Calculation of Form Parameters This Appendix explains how the calculation of form parameters (CB, CP, AM, etc.) is achieved in Maxsurf Stability, and investigates why differences with other hydrostatics packages may occur.

Definition and calculation of form parameters Below is a summary of the definitions of basic vessel particulars and form parameters used in Maxsurf Stability. Measurement Reference Frames

Results in Maxsurf Stability are given from the vessel’s zero point. However, because Maxsurf Stability treats trim exactly (the hull is rotated not sheared when trim occurs), there are two frames of reference: Ship or upright frame of reference The “ship” or “upright” reference frame is that of the upright vessel with zero-trim. Here the baseline is horizontal and the perpendiculars are vertical. “Longitudinal” measurements are made parallel to the baseline and “vertical” measurements are perpendicular to the baseline. World or trimmed frame of reference The “world” or “trimmed” reference frame is that of the trimmed vessel. Here the baseline is no longer horizontal and neither are the perpendiculars vertical. “Longitudinal” measurements are made parallel to the horizontal, static waterline and “vertical” measurements are perpendicular to the waterline

Rotated reference frame (red) and measurements in the two reference frames: Measurements in the upright vessel reference frame (green) and trimmed reference frame (blue)

When the vessel is upright (zero trim and zero heel) these axis systems are parallel. However if the vessel is trimmed or heeled or rotated in both directions simultaneously, these axis systems are no longer parallel.

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Appendix A

Ship-Fixed and Earth-Fixed(world) axis systems

The majority of measurements are given in the “ship” frame of reference. These include longitudinal centres of gravity, floatation and buoyancy (LCG, LCF, LCB); and measurements from the keel such as KB and KG. Measurements such as BM, GM, that are explicitly vertical, are measured in the “world” frame of reference, i.e. GM is the true vertical separation of the metacentre and the centre of gravity with the vessel inclined and are always measured normal to the water surface. Thus the metacentre is always vertically (in the earth-fixed axis system) above the centre of buoyancy by a distance BM = I / vol where I is the second moment of area of the waterplane. It is for this reason that, in general, KM is not equal to KB+BM (BM is in a different axis system to KB and KM, and only if the vessel is upright are the axis systems parallel and hence the equation holds). Similarly, in generally for the vessel to be in equilibrium, LCG is not equal to LCB – if both LCB and LCG are measured in the ship-axis system (of course if they are measured in the earthfixed axis system then they are the same. This is because if the vessel is trimmed and if the VCG and VCB are not the same, then there will be a sin(trim angle) term introduced. The same is true of TCB and TCG if the vessel is heeled.

Page 263

Appendix A Nomenclature

Amax Ams A AWP BOA BWL B b GM

KB KG LOA LCB LCF LCG LWL LBP L T0 T t 

Maximum immersed cross-sectional area to waterline under investigation Immersed cross-sectional area to waterline under investigation amidships Immersed cross-section area: Amax or Ams as selected by user Area of waterplane at the waterline under investigation Overall beam of whole vessel (above and below waterline) Maximum waterline beam at design waterline Maximum beam of waterline under investigation Waterline beam of station under investigation Metacentric height: vertical distance from centre of gravity to metacentre, measured in the trimmed reference frame Distance from keel (baseline) to centre of buoyancy, measured normal to the baseline. Distance from keel (baseline) to centre of gravity, measured normal to the baseline. Length overall Longitudinal Centre of Buoyancy, measured in upright reference frame, parallel to baseline. Longitudinal Centre of Floatation, measured in upright reference frame, parallel to baseline. Longitudinal Centre of Gravity, measured in upright reference frame, parallel to baseline. Length of design waterline Length between perpendiculars length of waterline under investigation Draft from some arbitrary baseline (normally the lowest point on the design) Maximum immersed depth (draft) of hull Draft (immersed depth) of station under investigation Immersed volume of displacement at waterline under investigation

Coefficient parameters

There are several options for calculating hullform coefficients. These can be modified in the Data | Coefficients dialog shown below:

Page 264

Appendix A

Length

The datum/design waterline or DWL is a waterline near which the fully loaded design is intended to float under normal circumstances. The forward perpendicular is normally defined as the intersection of the DWL with the bow. The after perpendicular is normally defined as the position of the rudder post, or possibly the transom. Several lengths may be defined: the LBP is the length between perpendiculars, this may be different from the length of the DWL (LWL) and in general, will also be different from the LOA (overall length). In some cases, particularly for resistance prediction purposes, it may be more appropriate to define an effective length of the underwater body, features such as bulbous bows and overhangs can make the LBP, LWL and LOA quite different. In addition, for calculations at drafts other than the DWL, it may be appropriate to use the actual waterline length at that draft (L).

Some of the more common lengths that may be used to characterise a vessel.

In Maxsurf Stability you may choose between the length between perpendiculars and the waterline length for the calculation of Block, Prismatic and Waterplane Area Coefficients. Select Coefficients from the Display menu:

Page 265

Appendix A

Beam

It is normal to use the maximum waterline beam for calculation of coefficients, and this may be of the DWL or the waterline under consideration. However, there may be times when it is appropriate to use the maximum immersed beam (e.g. submarine, vessel with tumble-home or blisters). For the calculation of section area coefficients it is normal practice to use the beam and draft of the section in question.

Vessel with tumble-home

Catamarans and other multihull vessels pose another difficulty. In some cases the overall beam is of importance, in others, the beam of the individual hulls may be required. Maxsurf Stability uses the total waterline beam of immersed portions of the section for calculation of block coefficient and other form parameters. For the case of a monohull this will be the normal waterline beam. For catamarans this will be twice the demihull beam (remember that the total displaced volume is used and hence the block coefficient is the same as that of a single demihull). For the section shown below, the beam used would be the sum of B1, B2 and B3.

Multihull beams

You may choose which beam should be used from the following list:

In the reported hydrostatics, you can select various beams: Page 266

Appendix A

Calculated beams

The values “Beam extents” are those that measure the beam across the maximum port and starboard extents of the vessel. For a catamaran this would be from the outside of the port demihull to the outside of the starboard demihull. For a monhull, this would simply be the distance from the port side to the starboard side. The other beam values are calculated by summing the breadth of waterline crossings as described above. For a monhull without tunnels, this will be the same as the extents value, but for a multihull, it will be less than the extents value. Maxsurf Stability uses these values for computing coefficients. Draft

The draft is normally specified from a nominal datum. Normally this datum is the lowest part of the upright hull. However, for vessels with raked keel lines or yachts, the datum may be elsewhere. In Maxsurf Stability drafts are defined from the datum line. However, there are also occasions when the immersed depth of the section is a more relevant measure of draft, this is often the case when form parameters are calculated. Maxsurf Stability uses the depths that stations extend below the waterline for calculation of form coefficients. Both depths are measured in upright position. You may select which depth should be used for the calculation of form parameters, including the option of measuring the draft to the baseline – this gives the option of ignoring appendages such as fin keels when determining the draft to be used to calculate the form parameter (if the baseline is defined to the bottom of the canoe body for example). It should be noted that the section area will, however, include the appendages.:

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Appendix A Draft measurements

Draft measurement at heel angle When the vessel is heeled, the draft is measured through the intersection of the upright waterline and the centreline, perpendicular to the heeled waterline (see figure below). Essentially the draft is measured along the heeled and trimmed perpendiculars on the centreline. It is for this reason that as the heel approaches 90degrees, the draft becomes very large.

Draft measured along the inclined perpendicular lines

Immersed depth and Draft measurements The images below show the difference between the draft measurements (which are made in the inclined centreline plane of the vessel) and the immersed depth measurements (which are made normal to the free-surface).

Difference between “Immersed depth” and “Draft” measurements

Midship and Max Area Sections

It is current usual practice to define the midship section as midway between the perpendiculars, however for some vessels it is defined as the midpoint of the DWL. For vessels with no parallel mid-body, the section with greatest cross-sectional area may also be of particular interest. In Maxsurf Stability, the position midway between the perpendiculars is defined as midships.

Page 268

Appendix A

When computing form coefficients, such as CP and CM, you may select which section area should be used: Maxsurf Stability uses the station with the maximum immersed cross-sectional area at the waterline under consideration.

Block Coefficient

Principles of Naval Architecture defines the block coefficient as: “the ratio of the volume of displacement of the moulded form up to any waterline to the volume of a rectangular prism with length, breadth and depth equal to the length, breadth and mean draft of the ship at that waterline.” However, the actual definitions of the length, beam and draft used vary between authorities. Length may be LBP, LWL or some effective length. The beam may be at amidships or the maximum moulded beam of the waterline; or may be defined according to another standard – this may be important for hulls with significant tumble-home or blisters below the waterline. Maxsurf Stability uses the length beam and draft as selected in the Coefficients dialog to compute the block coefficient. The beam used is that obtained by summing the immersed waterline crossings of the specified section.

CB 

 L  B T

Section Area Coefficient

Principles of Naval Architecture defines the midship coefficient as: “The ratio of the immersed area of the midship station to that of a rectangle of breadth equal to moulded breadth and depth equal to moulded draft at amidships.” It should be noted that, for sections that have significant tumble-home or blisters below the waterline, the midship section coefficient can be greater than unity. In Maxsurf Stability midships is midway between the perpendiculars. The section area coefficient used by Maxsurf Stability, is calculated at either the station with maximum cross-sectional area or the midship section area (as defined in the Coefficients dialog). The beam and immersed depth of the selected section is used unless the draft to baseline option has been selected in which case this draft is used.

Options for Section area coefficient

CM 

A bt

Prismatic Coefficient

Principles of Naval Architecture defines the prismatic coefficient as:

Page 269

Appendix A

“The ratio between the volume of displacement and a prism whose length equals the length of the ship and whose cross-section equals the midship section area.” Again the definition of midship section and vessel length depend on the standard being used. Maxsurf Stability uses the selected length and the selected immersed cross-section area Amax or Ams.

CP 

 L A

Waterplane Area Coefficient

Principles of Naval Architecture defines the waterplane area coefficient as: “The ratio between the area of the waterplane and the area of a circumscribing rectangle.” Maxsurf Stability uses the length and beam as selected.

CWP 

AWP LB

LCG and LCB

Maxsurf Stability allows you to fully customise how you want to display the LCB and LCF values. See Customising Coefficients on page 42 for more information. The LCG and LCB are calculated in the “ship” or “upright” frame of reference; see Measurement Reference Frames on page 262. When the vessel is free-to-trim, the LCG and LCB will be at the same longitudinal position in the global coordinate system, but not in the frame of reference. Therefore a difference between the LCG and the LCB value will occur when the vessel is trimmed. This is explained in the figure below:

Effect of vertical separation of CG and CB on LCG and LCB measured in the Ship reference frame

Page 270

Appendix A

Note: LCG and LCB are calculated in the vessels’ frame of reference and therefore will have different longitudinal positions when the vessel is trimmed then for when it is upright. This is the same for differences in TCG and TCB values due to heeling. Trim angle

The trim angle as defined by:

 Ta  T f    L pp  

  tan 1 

where:  is the trim angle; Ta , Tf are the aft and forward drafts at the corresponding perpendiculars and LPP is the length between perpendiculars. Maximum deck inclination

The inclination angle is a combination of heel and trim angle. Maxsurf Stability calculates the steepest slope of the deck when the ship is trimmed and/or heeled. Deck camber and initial deck slope are not taken into account. For example:

The Max deck inclination is the maximum slope of the deck when combining the trim and heel angle of the vessel, assuming the deck inclination is zero when the vessel is in upright position.

Immersion

The weight required to sink the model one unit-length below its current waterline. The unitlength can be either in cm or inch depending on your unit settings. MTc or MTi

The required moment to make the vessel trim one unit-length. That can be either cm or inch depending on your unit settings.

Page 271

Appendix A RM at 1 deg

The righting Moment at 1 degree heel angle, calculated by

RM  Displ *GMt * sin(1)

Potential for errors in hydrostatic calculations There are a number of potential sources of error when calculating the hydrostatic properties of immersed shapes. These mainly occur from the integration method used, and occur in both hand calculations, and most automatic calculations carried out by computers. Both methods use numerical integration techniques, which are normally either based on Simpson’s rule or the Trapezium rule. As with all numerical integration schemes, the accuracy increases as the step size is reduced, hence computer calculations offer an enormous advantage compared with hand calculations, due to the increased speed and accuracy with which these calculations may be carried out. With hand calculations, it is normal to use perhaps 21 sections and perhaps 3-5 significant figures; with computer calculations, it is quite feasible to use 200 sections or more with 10s of significant figures. These effects are noted from comparing the results of different hydrostatics packages on the same hullform. In general, differences for basic parameters such as displacement etc. are under 0.5% (note that, in general, agreement of hand calculations to within 2% is considered good). Differences in derived form parameters may show considerable variation. However, this is primarily due to differences in the definitions used – see discussion above. The 0.5% error discrepancy noted above, may be attributed to a number of causes:  Convergence limits when balancing a hull to a specified displacement or centre of gravity.  Different number of integration stations used, and their distribution. Where there are large changes in shape, such as near the bow and stern, the stations should be more closely spaced. This can be of particular importance if the waterline intersects the stem profile between two sections.

 Differences in the hull definition, and number of interpolation points used to define each section. If the surface is exported as DXF poly-lines then the precision used and the number of straight-line sections used to make up the poly-line are important.

 The integration method used: trapezium, Simpson, or higher order methods. Integration of wetted surface area

At first glance, it may seem that wetted surface area may be calculated by simply integrating the station girth along the length of the hull, in a similar way that one might integrate the station cross-sectional area along the length of the hull to obtain the volume. However, this is not the case, and the wetted surface area can only be accurately found by summing elemental areas over the complete surface. Further, the error due to integrating girths along the vessel length cannot be removed simply by increasing the number of integration stations. The only accurate numerical method is to sum the areas of individual triangles interpolated on the parametric surface. The differences are easily shown by considering the surface area of half a sphere. This is given analytically by: A  2R 2 , where R is the radius of the circle. It may be shown that the area obtained by integrating the girth of the sphere along its length is given by:

A' 

 2R2 2

, note that this is with an infinite number of integration steps, and hence the

2R 2  4 /   1.27 , or integration of section girths underestimates by error factor of 0.5 2 R 2 approximately 27%. Page 272

Appendix A

However, for normal ship hulls the differences will be much less, due to the greatly reduced longitudinal curvature. Surface areas calculated by the ‘Calculate Areas’ dialog in Maxsurf are the most accurate, since they are derived from the actual parametric definition of the surface. Those calculated by Maxsurf Stability and most other hydrodynamics packages, which use a number of vertical stations to define the hull, will be subject to the error described above.

Page 273

Appendix B

Appendix B: Criteria file format The criteria are saved in a Maxsurf Stability criteria file with the extension .hcr. The file is a normal PC text file, which may be edited manually so as to generate custom criteria. The typical format of the file is given below: Please refer to the file C:\Program Files\Maxsurf\HMCriteriaHelp\CriteriaHelp.html for a full list of all the parameters for all the different criteria types. Maxsurf Stability Criteria File [units] LengthUnits = m MassUnits = tonne SpeedUnits = kts AngleUnits = deg GZAreaGMAngleUnits = deg [end] [criterionGroup] GroupName = Specific Criteria ParentGroupName = root [end] [criterionGroup] GroupName = My Custom Criteria ParentGroupName = root [end] [criterionGroup] GroupName = STIX input data ParentGroupName = Specific Criteria [end] [criterion] Type RuleName CritName CritInfo CritInfoFile Locked GroupName TestIntact TestDamage Test Compare UseLoHeel UseEquilibrium UseHiHeel UseFirstPeak UseMaxGZ UseFirstDF UseVanishingStab LoHeel HiHeel RequiredValue [end]

Page 274

= = = = = = = = = = = = = = = = = = = = =

CTStdAreaUnderGZBetweenLimits STIX input data GZ area to the lesser of downflooding or… Area under GZ curve between specified heel… HMCriteriaHelp\StixHelp.rtf true STIX input data true false false GreaterThan false true false false false true true 0.0 30.0 0.000

Appendix B

[criterion] Type RuleName CritName CritInfo CritInfoFile Locked GroupName TestIntact TestDamage Test Compare RequiredValue [end]

= = = = = = = = = = = =

CTStdAngleOfVanishingStab STIX input data Angle of vanishing stability Calculates the angle of vanishing stability… HMCriteriaHelp\StixHelp.rtf true STIX input data true false false GreaterThan 0.0

The file must have “Maxsurf Stability Criteria File” in the first row. The first section of the file is the units section and this specifies the units that are to be used in the file. There are two angular units: AngleUnits Specifies the units for angular measurements, e.g. range of stability GZAreaGMAngleUnits Specifies the angle units used for area under GZ graph and for GM. The criteria then appear after the units section and as many criteria as required may be included. The common parameters for all criteria are as follows: Type Describes the type of criterion RuleName Text which specifies the rule to which the criterion belongs CritName Text which specifies the criterion’s name CritInfo Verbose description of the criterion Locked Whether the criterion may be edited in Maxsurf Stability or not. If Locked is set to true, it is not possible to edit the criterion’s parameters in Maxsurf Stability The other parameters that may be set depend on the criterion type.

Page 275

Appendix F

Appendix C: Criteria Help In this Appendix all individual Parent Criteria are explained in detail. This information can also be found in the lower right of the Criteria Dialog in the Criteria Help section. In this section:  Parent Calculations  Minimum GM Calculators  Parent Heeling Arms  Parent Heeling Moments  Parent Stability Criteria

For all general help on criteria or working with the criteria dialog, see Chapter 4 Stability Criteria on page 209.

Parent Calculations Special calculations are provided for some criteria parameters. This allows for complex calculations to be cross referenced into criteria. Currently this has only been implemented for the IMO roll-back angle calculation used in the IMO code on Intact Stability, severe wind and rolling (weather) criterion; and the IMO required GM for vessels carrying grain in bulk. If there are any other calculations that you would like implemented, please contact us through www.bentley.com/serviceticketmanager with details of the required calculations. The parent calculations are listed above the parent heeling arms:

Parent calculations in Maxsurf Stability Criteria dialog

As with other criteria and heeling arms, you should make a copy of the parent calculation by dragging it to your custom criteria folder. Selecting a calculation in a criterion

Using a calculation in a criterion is very similar to using a heel arm:  Define your custom calculation by copying it from the parent list.  In the criterion select the required calculation from the pull down list:

Angle calculators

These calculators produce an angular measurement and may be referenced by the following criteria: Criteria that currently support roll-back angle calculations

Heeling arm criteria (xRef) Combined Page 276

Ratio of areas type 2

XRefHeelRatioOfAreas2

Combined criteria (ratio of areas

XRefHeelGenericWindHeeling

Appendix B

heeling arm criteria (xRef) Heeling arm criteria (stand alone) Heeling arm, combined criteria (stand alone) Heeling arm, combined criteria (stand alone)

type 2) Ratio of areas type 2 - general wind heeling arm

CritHeelRatioOfAreas2

Combined criteria (ratio of areas type 2) - general wind heeling arm

CritHeelGenericWindHeeling

Combined criteria (ratio of areas type 2) - wind heeling arm

CritHeelWindHeeling

IMO roll-back angle calculator

The IMO roll back angle calculator calculates the roll back angle as per the severe wind and rolling (weather) criterion as defined in the IMO Code on Intact Stability. The input parameters may be specified by the user or calculated by Maxsurf Stability for the vessel in the upright condition for the current loadcase. The block coefficient is calculated with the current user settings for length and beam (not necessarily the waterline beam which another parameter required for the calculation). The method used for the k-factor can be one of three options: “Round bilge: k = 1.0”, “Sharp bilge: k = 0.7” or “Tabulated value for k” – these are auto completed so you only need to type the first letter. This calculation follows the function defined in the Intact Stability codes A.749(18) and MSC.267(85).

Input parameters for: IMO roll-back angle calculation

GM calculators

These calculators produce a GM measurement and may be referenced by the following criteria: Criteria that currently support roll-back angle calculations

GZ curve criteria

Value of GMt at (calc)

CTStdValueOfGMAt

Minimum GM calculator – Grain

The required GM for vessels carrying grain, as defined in IMO Resolution MSC.23(59), is calculated as follows:

GM 



L  B  Vd 0.25B  0.645 B  Vd



0.0875  SF  

Where (using consistent units): L is the combined length of all full compartments Page 277

Appendix F

B is the moulded breadth of the vessel SF is the stowage factor Vd is the calculated average void depth Δ is the vessel displacement

Input parameters for: Grain heeling min. required GM Minimum GM calculator – Wind pressure

The GM required to withstand wind pressure is calculated as follows: 2  L  k 0     A(h  H ) cos n (0 )   k1   GM    sin(0 )

Where (using consistent units): L is the waterline length of the vessel (if the criterion required LPP or LOA then enter the value directly rather than having it calculated by Maxsurf Stability. Δ is the vessel displacement  0 is a critical heel angle which may be a fixed angle or a fraction of the deck-edge or marginline immersion angle A is the windage area which may be specified as a total area or as an area additional to the area of the hull above the waterline; h is height of the centroid of A above the zero point. H is the height of the assumed centre of lateral resistance of the vessel. k0 and k1 are constants, for example: For CFR 46, 170.170: ocean service: k0 = 0.005 Ton/ft2 and k1 = 14200 ft4/Ton k0 = 0.055 t/m2 and k1 = 1309 m4/t For CFR 46, 170.170: service on partially protected water: k0 = 0.0033 Ton/ft2 and k1 = 14200 ft4/Ton k0 = 0.036 t/m2 and k1 = 1309 m4/t For CFR 46, 170.170: service on protected water: k0 = 0.0025 Ton/ft2 and k1 = 14200 ft4/Ton k0 = 0.028 t/m2 and k1 = 1309 m4/t

Page 278

Appendix B

Input parameters for: Wind pressure min. required GM Minimum GM calculator – Constant

The required GM is calculated as follows:

GM 

a cos n (0 )  sin m (0 )

Where (using consistent units): a is a constant arm or moment (depending on whether the vessel displacement is used)  0 is a critical heel angle which may be a fixed angle or a fraction of the deck-edge or marginline immersion angle m, n are the exponents for sine and cosine. An example of where this calculation should be used is in CFR 46, 171.050:

GM 

Nb Nb with a  and m, n = 1.0 K tan(0 ) K

Where N is the number of passengers; b is their average transverse location and K is the number of passengers per unit mass.

Input parameters for: Constant min. required GM Minimum GM calculator – Constant with freeboard

The required GM is calculated as follows:

cos n (0 ) a B GM      f  f a  sin m (0 ) Where (using consistent units): Page 279

Appendix F

a is a constant arm or moment (depending on whether the vessel displacement is used) B is the vessel beam f is the minimum freeboard for the upright (zero heel) condition to the deck-edge or marginline. fa is the additional freeboard allowance calculated as follows (additionally the freeboard allowance may be limited to a maximum specified value):

fa  k  h 

l  2b  b0    b1  L  B 

Where (using consistent units): L is the waterline length of the vessel (if the criterion required LPP or LOA then enter the value directly rather than having it calculated by Maxsurf Stability. B is the same as that used in the expression for GM k is a dimensionless constant h is a height, typically the height of the watertight trunk l is a length, typically the length of the watertight trunk b is a breadth, typically the breadth of the watertight trunk b0 is a constant with the same units as b b1 is a dimensionless constant If desired, a heel adjustment may be included:  0 is a critical heel angle which may be a fixed angle or a fraction of the deck-edge or marginline immersion angle m, n are the exponents for sine and cosine.

Parent Heeling Arms As with the criteria, there is a list of parent heeling arms, from which custom heeling arms may be derived:

Available heeling arms and moments

To learn how to cross reference these heeling arms into criteria, please see Heeling arm criteria (xRef) on page 310. Heeling Arm Definition

This section describes how to define heeling arms and is valid for both the parent heeling arms that can be cross referenced into the heeling arm criteria, and for the Old heeling arm criteria where the heeling arm is specified for each criterion separately. Page 280

Appendix B

There are several heeling arms that are used for the criteria. They are defined below.  General heeling arm  General heeling arm with gust  General cos+sin heeling arm  User Defined heeling arm  Passenger crowding heeling arm  Wind heeling arm  Velocity Profile Wind heeling arm  Lifting heeling arm  Towing heeling arm  Forces heeling arm  Trawling heeling arm  Grain heeling arm  Areas and leavers  Important note: heeling arm criteria dependent on displacement

Note: When you are working with the parent heeling arms, make sure you copy them into a custom heeling arms folder before editing them. Same as for the Parent criteria, the Parent heeling arms will be reset to their default values each time you start up Maxsurf Stability. General heeling arm

The general form of the heeling arm is given below:

H ( )  A cos n ( ) where:

 is the heel angle, A is the magnitude of the heeling arm, cos n describes the shape of the curve. Typically n=1 is used for passenger crowding and vessel turning since the horizontal lever for the passenger transverse location reduces with the cosine of the heel angle. For wind n=2 is often used for heeling because both the projected area as well as the lever decrease with the cosine of the heel angle. However, some criteria, such as IMO Severe wind and rolling (weather criterion) have a heeling arm of constant magnitude, in this case n=0 should be used. Make sure you read Important note: heeling arm criteria dependent on displacement on page 290. General heeling arm with gust

Some criteria require a Gust Ratio, this is the ratio of the magnitude of the wind heeling arm during a gust to the magnitude of the wind heeling arm under steady wind.

GustRatio 

H gust H steady

Both the steady and the gust heel arm have the same shape.

H steady ( )  A cos n ( ) H gust ( )  A  GustRatio  cos n ( )

Page 281

Appendix F

where:

 is the heel angle, A is the magnitude of the heeling arm, cos n describes the shape of the curve. It should be noted, that in this case, the definition of gust ratio is the ratio of the heeling arms. Some criteria specify the ratio of the wind speeds; if it is assumed that the wind pressure is proportional to the square of the wind seed, the ratio of the heel arms will be the square of the ratio of the wind speeds. General cos+sin heeling arm

Some criteria, notably lifting of weights, require a heeling arm with both a sine and cosine component:



H ( )  k A cos n ( )  B sin m ( )



It should be noted that provided the indices are both unity, the same heeling arm form may be used for computing towing heeling arms of the form:

H ( )  k  A cos(   )  B sin(   )

in this case a constant angle (in the case of towing, the angle of the tow above the horizontal) is included. It may be shown that this is equivalent to:

H ( )  k C cos( )  D sin( )

where:

C

R2 B tan   2 2 2 2 1  tan (   ) , D  C tan(   ) , R  A  B and A

Make sure you read Important note: heeling arm criteria dependent on displacement on page 290. User Defined heeling arm

A user-defined heeling arm may be used in the criteria. With the heeling arm, the user can specify the number of points and the shape of the heeling arm curve. This heeling arm can then be cross-referenced into any of the heeling arm criteria. First, the number of points is specified and then for each point the angle and magnitude of the curve can be specified. These should be comma delimited for example for a heeling arm magnitude of 1.2 meters at 45 degrees angle of heel. (To aid input of the data, if only one value is supplied it is taken as the heel angle – and the magnitude is left unchanged, and if a value preceded by a comma is given, this is taken as the magnitude – and the heel angle is left unchanged.) A single coefficient may be adjusted and this is used as a multiplication factor (whist the shape of the curve remains unchanged).

Page 282

Appendix B

Passenger crowding heeling arm

The magnitude of the heel arm is given by:

H pc ( ) 

n pas MD 

cos n ( )

where:

n pas is the number of passengers M is the average mass of a single passenger D is the average distance of passengers from the vessel centreline  is the vessel mass (same units as M ) The heeling arm parameters are specified as follows: Option number of passengers: nPass

Description Number of passengers

Units none

passenger mass: M distance from centreline: D cosine power: n

Average mass of one passenger Average distance of the passengers from the centreline Cosine power for curve - defines shape

mass length none

Wind heeling arm

In the case of the wind pressure based formulation, the wind heeling arm is given by:

H w ( )  a

PAh  H  n cos ( ) g

where: a is a constant, theoretically unity A is the windage area at height h  is the vessel mass P is the wind pressure H is the vertical centre of hydrodynamic resistance to the wind force In the case of the wind velocity based formulation, the wind heeling arm is given by:

Page 283

Appendix F

H w ( )  a

v 2 Ah  H  n cos ( ) g

where: a is now effectively an average drag coefficient for the windage area multiplied by the air density and has units of density v is the wind speed. And the other parameters are described as above. Option constant: a

Description Constant which may be used to modify the magnitude of the heel arm, normally unity for pressure based formulation or 0.5 ρair CD for the velocity formulation; where ρair is the density of air and CD is an average drag coefficient for the windage area

wind model

Pressure or Velocity (type “P” or “V”)

wind pressure or velocity

Actual velocity of pressure - depends on wind model

area centroid height: h

Height of user defined total or additional windage area User may specify either a total windage area Or, an area to be added to the windage area computed by Maxsurf Stability based on the hull sections There are four options for specifying H (all options are calculated with the vessel upright at the loadcase displacement and LCG): User specified H is taken as half the mean draft. H is taken as the vertical centre of underwater lateral projected area.

total area: A additional area: A

height of lateral resistance: H

H = mean draft / 2 H = vert. centre of projected lat. u’water area H = waterline cosine power: n

H is taken as the waterline Cosine power for curve - defines shape

Units none for pressure based formulation; mass/length3 for velocity based formulation

mass/(time2 length) or length/ time length length2 length2

length

length length

length none

Velocity profile wind heeling arm

A new criterion wind heeling arm has been added that allows the definition of a vertical velocity to be specified. This heeling arm is always velocity-based (not pressure-based); furthermore only the model-defined windage profile is used (there is no option for additional area).

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Appendix B

Wind heeling arm with velocity profile option

The velocity profile is defined by a series of horizontal strips parallel and above the waterline. Each strip has a factors which is applied to the base velocity. This is done so that the same velocity profile can easily be maintained for different base wind velocities. To apply a uniform velocity profile (constant velocity at all heights) then simply specify

Uniform velocity profile

For a variable velocity profile simply specify the number of heights and the factor for each height range: When entering the data for the velcity profile enter: "height , factor". Heights must be in descending order. A height can he changed by typing "height"; a factor can be changed by typing ", factor"

Variable velocity profile

When a variable velocity profile is selected for display, the different height zones are displayed.

Wind profile showing height zones defined in the selected variable wind velocity heeling arm

The wind heeling moment is calculated by dividing the windage profile in to the defined height zones and applying the velocity profile. This is done for all the windage groups whose contributions are then summed to give the total wind heeling moment. This is divided by the vessel displacement to obtain the total wind heeling arm. Thus the wind heeling arm, arm wind , is given by:

arm wind 

  a. cos n ( ) 2 v. f height   Ftotal group. Agroup.(hgroup  H )   g. heights groups 





where: Page 285

Appendix F

a is a constant (typically half the density of air); cos n ( ) defines the shape of the heeling arm (typically this would be 0.0 if the calculation of the actual windage profile at each heel angle option has been selected); g. is the weight-force of the vessel;

 ... accounts for the summation over all the height intervals specified for the velocity

heights

profile, with a base velocity of v and a factor at each height f height ;

 ... accounts for the summation over all the defined windage groups;

groups

Ftotal group is the total factor for the windage group defined as Ftotal  Fdrag .1.0  Fshield .Fuser Agroup is the area of the windage group

hgroup is the vertical height of the center of area of the windage group H is the height to be used for the assumed center of lateral resistance of the underwater part of the hull. Turning heeling arm

The magnitude of the heel arm is derived from the moment created by the centripetal force acting on the vessel during a high-speed turn and the vertical separation of the centres of gravity and hydrodynamic lateral resistance to the turn. The heeling arm is obtained by dividing the heeling moment by the vessel weight. The heeling arm is thus given by:

H t ( )  a

v2 h cos n ( ) Rg

where (in consistent units): a is a constant, theoretically unity v is the vessel velocity R is the radius of the turn h is the vertical separation of the centres of gravity and lateral resistance The heeling arm parameters are specified as follows: Option constant: a vessel speed: v turn radius: R turn radius, R, as percentage of LWL Vertical lever: h

h = KG h = KG - mean draft / 2 h = KG - vert. centre of projected lat. u’water area cosine power: n

Page 286

Description Constant which may be used to modify the magnitude of the heel arm, normally unity Vessel speed in turn Turn radius may be specified directly Or, as some criteria require, as percentage of LWL There are four options for specifying h (all options are calculated with the vessel upright at the loadcase displacement and LCG): User specified h is taken as KG - position of G above baseline in upright condition h is taken as KG less half the mean draft. h is taken as the vertical separation of the centres of gravity and underwater lateral projected area. Cosine power for curve - defines shape

Units none length/time length % length

length length length

none

Appendix B Lifting heeling arm

This is used to simulate the effect of lifting a weight from its stowage position. (The weight is lifted from a stowage position onboard the vessel by a crane on the vessel; i.e. the vessel displacement remains constant, but there is an effective change of its centre of gravity.) The magnitude of the heel arm is given by:

H lw ( ) 

M h cos( )  v sin( ) 

where: M is the mass of the weight being lifted h is horizontal separation of the centre of gravity of the weight in its stowage position and the suspension position (upper tip of lifting boom) v is vertical separation of the centre of gravity of the weight in its stowage position and the suspension position (upper tip of lifting boom)  is the vessel mass (same units as M )

Just before lifting the weight off the vessel’s deck

The heeling arm parameters are specified as follows: Option Mass being lifted: M vertical separation of suspension from stowage position: v

horizontal separation of suspension from stowage position: h

Description Mass of weight being lifted Vertical separation of suspension point from weight’s original stowage position on the vessel. This value is positive if the suspension position (upper tip of lifting boom) is above the original stowage position. Horizontal separation of suspension point (upper tip of lifting boom) from weight’s original stowage position on the vessel This value is positive if the horizontal shift of the weight should produce a positive heeling moment.

Units mass length

length

Towing heeling arm

The magnitude of the heel arm is given by:

H tow ( ) 



T v cos n (   )  h sin(   ) g



where: T is the tension in the towline or vessel thrust, expressed as a force. h is horizontal offset of the tow attachment position from the vessel centreline Page 287

Appendix F

v is vertical separation tow attachment position from the vessel’s vertical centre of thrust  is the vessel mass n is the power index for the cosine term which may be used to change the shape of the heeling arm curve  is the (constant) angle of the towline above the horizontal. It is assumed that the towline is sufficiently long that this angle remains constant and does not vary as the vessel is heeled. The heeling arm parameters are specified as follows: Option tension or thrust: T vertical separation of propeller centre and tow attachment: v horizontal offset of tow attachment: h

angle of tow above horizontal: tau cosine power: n

Description Tension in towline or vessel thrust Vertical separation tow attachment position from the vessel’s vertical centre of thrust. This value is positive if the towline is above the thrust centre. Horizontal offset of the tow attachment position from the vessel centreline. This value is positive if the offset is in the direction of the tow. Angle of tow above the horizontal

Units force length

Cosine power for curve - defines shape

none

length

angle

Forces heeling arm

This heeling arm can be used to model up to two forces acting on the vessel forces, such as those applied due fire-fighting or manoeuvring using thrusters. The magnitude of the heel arm is given by:

H forces ( ) 



1 A1 h1  H cos n1 ( )  A2 h 2  H cos n2 ( ) g



where: A1 and A2 are two forces acting on the vessel, expressed as a force, not a mass. h1 and h2 are the vertical heights (from the zero point) at which these forces act.

n1 and n2 define the shapes of the heeling arms created by the two forces. H is the assumed vertical position of the vessel’s centre of lateral resistance (or the centre of rotation from which the forces are applied)  is the vessel mass g is acceleration due to gravity Trawling heeling arm

This heeling arm can be used model the effects of trawl net snagging as defined in Annex G of the Australian NSCV requirements:

H trawling ( ) 

m y cos n ( ) m

where: m is a mass parameter determined from the breaking load of the trawl gear and the downwards angle of the trawl net. y is the transverse distance of the line of action of the trawl wire from the vessel centreline n defines the shape of the heeling arm.  is the vessel mass

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Appendix B Grain heeling arm

This heeling arm can be used model the effects of bulk grain shift as defined in IMO Resolution MSC.23(59): The heeling arm is defined by a straight line through two points A, B. It is mirrored about the heel=0 axis and is not allowed to go below zero. Point A = (0 deg heel, λ0) Point B = ( 1 deg heel, α λ0)

i.e the heeling arm magnitude is reduced by a factor α at a heel angle of 1 . The equation of the line is given below:

 (1   )  H grain ( )  0 1  abs  1  

The heeling arm magnitude at zero heel, λ0, is given by:

0 

volHM StowFact  

Where: volHM is the assumed volumetric heeling moment due to transverse grain shift in units of Length3.Length; StowFact is the stowage factor in units of Length3/Mass; and  is the vessel mass Areas and levers

Some criteria require the evaluation of above and below water lateral projected areas and their vertical centroids. The user may also specify additional areas and vertical centroids or the total areas and vertical centroids. In all cases the vertical centroids are given in the Maxsurf/Maxsurf Stability co-ordinate system; i.e.: from the model’s vertical datum, positive upwards. The lateral projected area and its centroid of area are calculated for the upright vessel (zero heel) at the draft and trim defined in the loadcase or trim dialog. The area is calculated from the hydrostatic sections used by Maxsurf Stability; thus, increasing the number of sections will increase the accuracy of the area calculation; further, only “Hull” surfaces are included in the calculation - “Structure” surfaces are ignored. The vertical position of the keel, K, is assumed to be at the baseline (as set up in the Frame of Reference dialog), even if the baseline does not correspond to the physical bottom of the vessel.

Page 289

Appendix F Important note: heeling arm criteria dependent on displacement

Some heeling arm criteria are dependent on the displacement of the vessel for the calculation of the Heeling Arm. For example, the value “A” in:

H ( )  A cos n ( ) ,is manually calculated from:

A

M , where 

M = heeling moment Δ = displacement. For these types of heeling arms you should use the various heeling moment curves that are available – see below:

Heeling moment curves

Parent Heeling Moments

Heeling moments work the same way as the Minimum GM Calculations in that they can be cross referenced into criteria. The advantage of using heeling moments is that they provide a constant heeling moment (varying heeling arm) as the vessel displacement changes (due to different loadcases or during a limiting KG analysis). These are in addition to the existing specific heeling arm curves for passenger crowding, wind heeling etc., which take account of the vessel displacement as required. The following heeling moments are available in the Maxsurf Stability criteria dialog:  General heeling moment  General cos+sin heeling moment  General heeling moment with gust  User Defined Heeling Moment General heeling moment

The general form of the heeling moment is given below. It allows you to specify a constant heeling moment as opposed to a constant heeling arm:

H ( )  where:

A cos n ( ) 

 is the heel angle, A is the magnitude of the heeling moment (mass.length) and  the vessel displacement A (mass); thus is the magnitude of the heeling arm (length).  cos n describes the shape of the curve.

Page 290

Appendix B

Typically n=1 is used for passenger crowding and vessel turning since the horizontal lever for the passenger transverse location reduces with the cosine of the heel angle. For wind n=2 is often used for heeling because both the projected area as well as the lever decrease with the cosine of the heel angle. However, some criteria, such as IMO Severe wind and rolling (weather criterion) have a heeling arm of constant magnitude, in this case n=0 should be used. General cos+sin heeling moment

Some criteria, notably lifting of weights, require a heeling moment with both a sine and cosine component:

H ( ) 



k A cos n ( )  B sin m ( ) 



where:

 is the heel angle, A and B the magnitudes of the cosine and sine components of the heeling moment A and B are the magnitude of the (mass.length) and  the vessel displacement (mass); thus   heeling arm (length). It should be noted that provided the n and m indices are both unity, the same heeling moment form may be used for computing towing heeling moments of the form:

H ( ) 

k  A cos(   )  B sin(   ) 

in this case a constant angle (in the case of towing, the angle of the tow above the horizontal) is included. It may be shown that this is equivalent to:

H ( ) 

k C cos( )  D sin( ) 

where:

C

R2 B 1  tan 2 (   ) , D  C tan(   ) , R 2  A2  B 2 and tan   A

General heeling moment with gust

Some criteria require a Gust Ratio, this is the ratio of the magnitude of the wind heeling arm during a gust to the magnitude of the wind heeling arm under steady wind.

GustRatio 

H gust H steady

The general form of the heeling moment is given below. It allows you to specify a constant heeling moment as opposed to a constant heeling arm. Both the steady and the gust heel moment have the same shape.

A cos n ( )  A H gust ( )   GustRatio cos n ( ) 

H steady ( ) 

where:

 is the heel angle, Page 291

Appendix F

A is the magnitude of the heeling moment (mass.length) and  the vessel displacement A is the magnitude of the heeling arm (length). (mass); thus  n cos describes the shape of the curve. It should be noted, that in this case, the definition of gust ratio is the ratio of the heeling arms. Some criteria specify the ratio of the wind speeds; if it is assumed that the wind pressure is proportional to the square of the wind seed, the ratio of the heel arms will be the square of the ratio of the wind speeds. User Defined Heeling Moment

With the User Defined Heeling Moment, the user can specify the number of points and the shape of the heeling moment curve. Defining User Defined Heeling Moments works in much the same as for User Defined heeling arm. This heeling moment can then be linked into a Heeling arm criteria (xRef) for evaluation.

Parent Stability Criteria The parent criteria are divided up into different categories depending on their basic types. Criteria at Equilibrium

These criteria are calculated after an equilibrium analysis and relate to the equilibrium position of the vessel after the analysis. The equilibrium criteria are only displayed in the report if you run an equilibrium analysis. Maximum value of Heel, Trim or Slope at Equilibrium

This criterion may be used to check the value of maximum Heel, Pitch or Maximum Slope (compared with an originally horizontal and flat deck). Option The angle of

Shall be less than / Shall not be greater than

Description Choose from the following (case insensitive auto-completion is used): Heel Pitch MaxSlope Permissible value

Units deg

deg

Minimum Freeboard at Equilibrium

Checks whether the minimum freeboard is greater than a minimum required value. This could be used to check margin line or downflooding point immersion. Option The value of

Shall be greater than / Shall not be less than Page 292

Description Choose from the following (case insensitive auto-completion is used): Marginline DeckEdge DownfloodingPoints PotentialDfloodingPoints EmbarkationPoints ImmersionPoints Permissible value

Units length

length

Appendix B Maximum Freeboard at Equilibrium

Check that the maximum freeboard is less than a maximum required value. This could be used to check that an embarkation point is sufficiently close to the waterline. Option The value of

Shall be greater than / Shall not be less than

Description Choose from the following (case insensitive auto-completion is used): Marginline DeckEdge DownfloodingPoints PotentialDfloodingPoints EmbarkationPoints ImmersionPoints Permissible value

Units length

length

To check that the freeboard lies within a specified range, use a combination of both forms of the minimum/maximum freeboard criteria. Value of GMT or GML at Equilibrium

This criterion is used to check that the GM (transverse or longitudinal) exceeds a specified minimum value. Option The value of

Shall be greater than / Shall not be less than

Description Choose from the following (case insensitive auto-completion is used): GMtransverse GMlongitudinal) Permissible value

Units length

length

GZ Curve Criteria (non-heeling arm)

These criteria, calculated from the GZ curve, are calculated from the Large Angle Stability analysis in Maxsurf Stability. Value of GMt at

Finds the value of GMt at either a specified heel angle or the equilibrium angle. The criterion is passed if the value of GMt is greater then the required value. GMt is computed from waterplane inertia and immersed volume (not the slope of the GZ curve as this is inaccurate if the heel angle resolution is insufficient). In addition to a fixed required value, you may also select a calculation to provide the required minimum GM. Option specified heel angle angle of equilibrium Select calculation from list Shall be greater than / Shall not be less than

Description Value of GMt at either User specified heel angle See Nomenclature Chose a calculation for the minimum required GM from a copy of one of the Parent calculations Permissible value

Units deg deg length

length

Page 293

Appendix F Value of GZ at

Finds the value of GZ at either a specified heel angle, first peak in GZ curve, angle of maximum GZ or the downflooding angle. The criterion is passed if the value of GZ is greater then the required value. Option specified heel angle angle of first GZ peak angle of maximum GZ first downflooding angle Shall be greater than / Shall not be less than

Description Value of GZ at either User specified heel angle See Nomenclature See Nomenclature See Nomenclature

Units

Permissible value

length

deg deg deg deg

Value of Maximum GZ

Finds the maximum value of GZ within a specified heel angle range. The criterion is passed if the value of GZ is greater than the required value. If you want to check the value of GZ at a certain angle you can set both specified angles as the required angle. If any of the calculated angles for the upper limit are less than the lower limit, they will be ignored when selecting the lowest. If all the upper limit values are less than the lower limit, then the criterion will fail. This functionality is to allow criteria such as “The maximum GZ at 30deg or greater”. Note: Upper limit and analysis heel angle range It is required that the range of heel angles specified for the Large Angle Stability analysis is equal, or exceeds, the upper range heel angle specified in the criterion. Option in the range from the greater of specified heel angle angle of equilibrium to the lesser of specified heel angle

angle of first GZ peak angle of maximum GZ first downflooding angle Shall be greater than / Shall not be less than

Page 294

Description Value of maximum GZ Lower limit for heel angle range, the greater of the following: User specified heel angle See Nomenclature Upper limit for heel angle range, the lesser of the following: User specified heel angle; this should normally be specified and be less than or equal to the upper limit of the range of heel angles used for the Large Angle Stability analysis. See Nomenclature See Nomenclature See Nomenclature

Units

Permissible value

length

deg

deg

deg deg deg

Appendix B

Value of Maximum GZ Value of GZ at Specified Angle or Maximum GZ below Specified Angle

If the angle at which maximum GZ occurs is greater than a specified value, the value of GZ at the specified angle is calculated. Otherwise the value of maximum GZ is calculated. The required GZ value depends on the angle at which the maximum occurs, see graph below. Option heel angle at which required GZ is constant

Description If the angle of maximum GZ is greater than or equal to this value, the required value of GZ is constant and is taken at this specified angle. Otherwise the required value of maximum GZ varies as a hyperbolic function with the angle of maximum GZ. This is  0 .

Units Deg

required value of GZ at this angle is

Required value of GZ at the heel angle specified above. This is GZ  0  .

Length

limited by first GZ peak angle

Angle at which GZ is measured may be limited to the location of the first peak in the GZ curve. Angle at which GZ is measured may be limited to first downflooding angle. Permissible value.

deg

limited by first downflooding angle Shall be greater than / Shall not be less than

deg length

If GZ   0 then GZ  0  must be greater than the specified, constant value. max

Page 295

Appendix F

If GZ   0 then GZ max must be greater than max

0  GZ

GZ  0 

max

where:  0 is the specified angle at which the required GZ value becomes a constant

GZ

is the heel angle at which the maximum GZ of value occurs max

GZ  0  is the GZ value at  0 and GZ max is the maximum value of GZ.

Variation of required GZ with angle of maximum GZ

The angle at which the GZ was measured is listed in the results. Value of RM at Specified Angle or Maximum RM Below Specified Angle

As above (Value of GZ at specified angle or maximum GZ below specified angle) except the righting moment rather than the righting lever is specified, measured and compared. The righting moment RM is given by:

RM  gGZ

where: is the vessel volume of displacement  is the density of the liquid the vessel is floating in  is acceleration due to gravity = 9.80665m/s2 g GZ is the righting lever. Ratio of GZ Values at Phi1 and Phi2

Calculates the ratio of the GZ values at two specified heel angles. The criterion is passed if the ratio is less then the required value.

Ratio 

GZ 1  GZ  2 

Option Phi1, first heel angle, the lesser of specified heel angle angle of first GZ peak Page 296

Description Ratio of GZ values at phi1 and phi2 First heel angle, the lesser of the following: User specified heel angle See Nomenclature

Units

deg deg

Appendix B

Option angle of maximum GZ first downflooding angle Phi2, second heel angle, the lesser of specified heel angle angle of first GZ peak angle of maximum GZ first downflooding angle Shall be less than / Shall not be greater than

Description See Nomenclature See Nomenclature

Units deg deg

Second heel angle, the lesser of the following: User specified heel angle See Nomenclature See Nomenclature See Nomenclature

deg deg deg deg

Permissible value

%

Ratio of GZ values at phi1 and phi2 Angle of Maximum GZ

Finds the angle at which the value of GZ is a maximum positive value, heel angle can be limited by first peak in GZ curve and/or first downflooding angle. The criterion is passed if the angle is greater then the required value. Option limited by first GZ peak angle limited by first downflooding angle Shall be greater than / Shall not be less than

Description Angle of maximum GZ The angle of maximum GZ shall not be greater than the angle at which the first GZ peak occurs The angle of maximum GZ shall not be greater than the angle at which the first downflooding occurs Permissible value

Units deg

deg

deg

Page 297

Appendix F Angle of Equilibrium

Finds the angle of equilibrium from the intersection of the GZ curve with the GZ=0 axis. The criterion is passed if the equilibrium angle is less then the required value. Option Shall be less than / Shall not be greater than

Description Angle of equilibrium Permissible value

Units deg

Ratio of equilibrium heel angle to the lesser of

The equilibrium angle and the lesser of the selected angles are compared. If the ratio is less than the required value, then the criterion is passed. Using a ratio gives more flexibility, e.g.: it is possible to check that the equilibrium angle does not exceed half (or any other fraction) the downflooding angle. The user may choose the type of Key point to define the downflooding angle (downflooding point, potential downflooding point, embarkation point, immersion point). If the equilibrium angle is negative, the user is advised that the vessel should be heeled in the opposite direction and the criterion is failed. Option spec. heel angle angle of margin line immersion angle of deck edge immersion first flooding angle of the angle of first GZ peak angle of max. GZ angle of vanishing stability Shall be less than / Shall not be greater than

Description Ratio of equilibrium angle to the lesser of: Specified heel angle Angle of first immersion of the margin line

Units

Angle of first immersion of the deck edge

deg

Smallest immersion angle of the specified type of Key Point Angle of first local peak in GZ curve Angle at which maximum GZ occurs Angle of vanishing stability

deg

Permissible value

%

deg deg

deg deg deg

Equilibrium heel angle satisfies either

This criterion is nothing more than two “Ratio of equilibrium heel angle to the lesser of” criteria. The actual criterion is passed if either of the individual criteria is passed. This type of criterion is used to formulate criteria such as: The maximum allowable angle of equilibrium is 15 degrees in the damage condition, but this can be allowed to increase to 17 degrees if the deck edge is not immersed. Angle of Downflooding

Finds the angle of first downflooding. The criterion is passed if the downflooding angle is greater then the required value. Option Shall be greater than / Shall not be less than

Page 298

Description Angle of downflooding Permissible value

Units deg

Appendix B Angle of immersion

Finds the first/minimum angle at which the selected key-point type immerses. The criterion is passed if the smallest angle at which the selected item immerses is greater then the required value. Option first flooding angle of the (key-point type)

Description Downflooding points Potential downflooding points Immersion points Embarkation points Permissible value

Auto-complete is used Shall be greater than / Shall not be less than

Units

deg

Angle of Margin Line Immersion

Finds the first/minimum angle at which the margin line immerses. The criterion is passed if the smallest angle at which the margin line immerses is greater then the required value. Option Shall be greater than / Shall not be less than

Description Angle of margin line immersion Permissible value

Units deg

Angle of Deck Edge Immersion

Finds the first/minimum angle at which the deck edge immerses. The criterion is passed if the smallest angle at which the deck edge immerses is greater then the required value. Option Shall be greater than / Shall not be less than

Description Angle of deck edge immersion Permissible value

Units deg

Angle of Vanishing Stability

Finds the angle of vanishing stability from the intersection of the GZ curve with the GZ=0 axis. The criterion is passed if the angle of vanishing stability is greater then the required value. Option Shall be less than / Shall not be greater than

Description Angle of vanishing stability Permissible value

Units deg

Range of Positive Stability

The angular range for which the GZ curve is positive is computed. The criterion is passed if the computed range is greater then the required value. Option from the greater of specified heel angle angle of equilibrium to the lesser of

Description Range of positive stability Lower limit User specified heel angle See Nomenclature Upper limit of the range

Units

deg deg

Page 299

Appendix F

Option first downflooding angle angle of vanishing stability Shall be greater than / Shall not be less than

Description See Nomenclature

Units deg

See Nomenclature

deg

Permissible value

deg

GZ Area between Limits type 1 - standard

The area below the GZ curve and above the GZ=0 axis is integrated between the selected limits and compared with a minimum required value. The criterion is passed if the area under the graph is greater than the required value. Option from the greater of specified heel angle angle of equilibrium to the lesser of specified heel angle spec. angle above equilibrium angle of first GZ peak angle of maximum GZ first downflooding angle immersion angle of Marginline or DeckEdge angle of vanishing stability Shall be greater than / Shall not be less than

Page 300

Description GZ area between limits type 1 - standard Lower limit for integration, from greatest angle of User specified heel angle See Nomenclature Upper limit of integration, from lesser angle of User specified heel angle User specified heel angle above the equilibrium heel angle See Nomenclature See Nomenclature See Nomenclature

Units

See Nomenclature

deg

See Nomenclature

deg

Permissible value

length.angle

deg deg

deg deg deg deg deg

Appendix B

GZ area between limits type 1 - standard GZ area between limits type 2- HSC monohull type

The area under the GZ curve is integrated between the specified limits. However the required minimum area depends on the upper integration limit. The required area is defined below and is based on the area required for IMO MSC.36(63) §2.3.3.2 and IMO A.749(18) §4.5.6.2.1. The criterion is passed if the computed area under the graph is greater then the required value. The required area is defined as follows: If  max   2 : required area = A2 ; If  max  1 : required area = A1 ; If 1   max Where:

 A  A2  2  max  A2   1      2 : required area =  2 1 ;

 max is the upper integration limit; A1 is the area under the GZ curve required at the specified lower heel angle 1 ; and A2 is the area under the GZ curve required at the specified higher heel angle  2 . For example, if the lower angle was 15 and the required area at this angle was 0.07m.rad and the upper angle was 30 and the required area at this angle was 0.055m.rad, then the required area would be given by:

 0.07  0.055  A  0.55   30   max   30  15  or simplifying:

A  0.55  0.001 30   max 

Page 301

Appendix F

Variation of required area with upper integration limit

Option

from the greater of specified heel angle angle of equilibrium to the lesser of specified heel angle spec. angle above equilibrium angle of first GZ peak angle of maximum GZ first downflooding angle angle of vanishing stability lower heel angle

required GZ area at lower heel angle higher heel angle required GZ area at higher heel angle Shall be greater than / Shall not be less than

Page 302

Description GZ area between limits type 2- HSC monohull type Lower limit for integration, from greatest angle of User specified heel angle See Nomenclature Upper limit of integration, from smallest angle of User specified heel angle User specified heel angle above the equilibrium heel angle See Nomenclature See Nomenclature See Nomenclature

Units

See Nomenclature

deg

Minimum angle that requires a GZ area greater than... Until this angle the required GZ area is constant Value of GZ area that is required until the lower heel angle Angle from which the required GZ area remains constant onwards Value of GZ area that is required from the higher heel angle onwards Permissible value

deg

deg deg

deg deg deg deg deg

length.angle deg length.angle length.angle

Appendix B

GZ area between limits type 2 - HSC monohull type GZ area between limits type 3 - HSC multihull type

The area under the GZ curve is integrated between the specified limits. However the required

 The required area is defined below 1 1 /(  max ). minimum area depends on the upper integrationAlimit and is based on the area required for IMO MSC.36 (63) Annex 7 §1.1. The criterion is passed if the computed area under the graph is greater than the required value. required area = A1 1 /  max  ; Where:

 max is the upper integration limit; A1 is the area under the GZ curve required at the specified heel angle 1 . For example, if the specified angle ( 1 ) was 30 and the required area at this angle ( A1 ) was 0.055m.rad, then the required area would be given by:

A  0.05530 / max 

Page 303

Appendix F

Variation of required area with upper integration limit

Option

from the greater of specified heel angle angle of equilibrium to the lesser of specified heel angle spec. angle above equilibrium angle of first GZ peak angle of maximum GZ first downflooding angle angle of vanishing stability higher heel angle required GZ area at higher heel angle Shall be greater than / Shall not be less than

Page 304

Description GZ area between limits type 3 - HSC multihull type Lower limit for integration, from greatest angle of User specified heel angle See Nomenclature Upper limit of integration, from lesser angle of User specified heel angle User specified heel angle above the equilibrium heel angle See Nomenclature See Nomenclature See Nomenclature

Units

See Nomenclature

deg

Heel angle at which required GZ area is specified Value of GZ area that is required until the higher heel angle Permissible value

deg

deg deg

deg deg deg deg deg

length.angle length.angle

Appendix B

GZ area between limits type 3 - HSC multihull type Ratio of GZ area between limits

This criterion calculates the ratio of the two areas between the GZ curve and the GZ=0 axis. 2

Area 1 Ratio = = absArea 2

 GZ  d

1

 4  abs  GZ  d     3 

, where “abs” means the absolute value of.

Option

Description Ratio of GZ area between limits

Units

Area 1 from the greater of

Area 1 lower integration limit, 1

specified heel angle angle of equilibrium Area 1 to the lesser of

User specified heel angle See Nomenclature Area 1 upper integration limit,  2

deg deg deg

specified heel angle angle of first GZ peak angle of maximum GZ first downflooding angle angle of vanishing stability Area 2 from the lesser of

User specified heel angle See Nomenclature See Nomenclature See Nomenclature See Nomenclature

deg deg deg deg deg

specified heel angle angle of first GZ peak angle of maximum GZ first downflooding angle angle of vanishing stability

User specified heel angle See Nomenclature See Nomenclature See Nomenclature See Nomenclature

Area 2 lower integration limit, 3 deg deg deg deg deg Page 305

Appendix F

Option Area 2 to

Description

specified heel angle Shall be greater than / Shall not be less than

User specified heel angle Permissible value

Units

Area 1 upper integration limit, 4 deg %

This criterion is designed to be calculated on the positive side of the GZ curve only; GZ areas below the GZ=0 axis on the negative heel angle side of the GZ curve are not considered positive. Typically, Area 1 would be from equilibrium to vanishing stability and Area 2 would be from vanishing stability to 180 deg, see graph below. In the example below, the lower and upper integration limits for Area 1 are equilibrium and vanishing stability, respectively and the limits for Area 2 are vanishing stability and 180 deg.

Ratio of GZ area between limits – Example 1

In the following example the upper limit for Area 1 has been set to the downflooding angle. The limits for Area 2 remain unchanged.

Page 306

Appendix B

Ratio of GZ area between limits – Example 2

In the final example, the lower integration range for Area 2 has been reduced to the downflooding angle. Note that Area 2 is now A1 – A2.

Ratio of GZ area between limits – Example 3 Ratio of positive to negative GZ area between limits

This criterion calculates the ratio of GZ area above the GZ=0 axis to that below the axis in the given heel angle range. Option

Description

Units Page 307

Appendix F

Option

in the heel angle range from to Shall be greater than / Shall not be less than

Ratio =

Description Ratio of positive to negative GZ area between limits User specified lower limit heel angle User specified upper limit heel angle Permissible value

Units

deg deg %

Area 1 , absArea 2

where “abs” means the absolute value of. And the areas are defined as follows: If both heel angle limits are ≥ zero: Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0. Area 1 is positive, Area 2 is negative.

Ratio of positive to negative GZ area between limits. Positive heel: lower limit = 0deg, upper limit = 180deg.

If both heel angle limits are < zero: Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0. Area 1 is positive, Area 2 is negative.

Page 308

Appendix B

Ratio of positive to negative GZ area between limits. Negative heel: lower limit = -180deg, upper limit = 0deg.

If the lower heel angle limit < zero, and the upper heel angle limit > zero (the upper limit is assumed to be greater than the lower limit): Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0 for heel angles ≥ 0 plus the area between the GZ curve and GZ=0 axis, where the value of GZ < 0 for heel angles < 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0 for heel angles ≥ 0 plus the area between the GZ curve and GZ=0 axis, where the value of GZ > 0 for heel angles < 0. Area 1 is positive, Area 2 is negative.

Ratio of positive to negative GZ area between limits. Positive and negative heel: lower limit = -180deg, upper limit = 180deg.

Page 309

Appendix F Subdivision Index s-factor - MSC 19(58)

Probabilistic damage s-factor according to MSC 19(58) Option Lower angle of range : the greater of

specified heel angle angle of equilibrium Upper angle of range: lesser of

specified heel angle spec. angle above equilibrium angle of first GZ peak angle of maximum GZ first downflooding angle immersion angle of Marginline or DeckEdge angle of vanishing stability Max. GZ limit Range limit

Description The greater of the selected angles is be to specify the lower limit of the range of positive stability and the range in which the maximum value of GZ should be found. User specified heel angle See Nomenclature The lowest of the selected angles is be to specify the upper limit of the range of positive stability and the range in which the maximum value of GZ should be found. See Nomenclature See Nomenclature

Units

See Nomenclature See Nomenclature See Nomenclature See Nomenclature

deg deg deg deg

See Nomenclature Upper limit of allowable maximum GZ value when computing s Upper limit of allowable range of positive stability when computing s

deg length

deg deg

deg deg

deg

S = C sqrt( 0.5 GZmax . range) Both the values of maximum GZ and range of positive stability can be clipped. Heeling arm criteria (xRef)

The cross-reference heeling arm criteria are set up to allow you to define heeling arms or heeling moments in a central location and then cross-reference or link them into the criteria. The criteria themselves work much the same as the Heeling arm criteria (page 311), except for the fact that you don’t have to specify the heeling arm for each criterion separately, but can simply select which heeling arm you wish to apply. After you have defined your heeling arms, these can be cross-referenced into new heeling arm criteria:

Page 310

Appendix B

The heeling arms are cross-referenced simply by selecting the desired heeling arm from the pull-down list:

For information on defining heeling arms or moments, see Minimum GM calculator - Grain on page 277. Heeling arm criteria

The preferred method is to use the xRef heeling arm criteria rather than the stand alone heeling arm criteria. This is because a wider range of heeling arm formulations is available and for some criteria, they only exist in xRef form. The heeling arm criteria available in the Maxsurf Stability Criteria dialog are listed below. Also available are:  Multiple heeling arm criteria; these are where the same criterion is applied to up to three heeling arms and/or combinations of these heeling arms

 Heeling Arm, combined criteria; these are where several criteria are applied to the same heeling arm Value of GMT at equilibrium - general heeling arm

Calculates the transverse metacentric height (GMT) at the intersection of the GZ and heel arm curves. The criterion is passed if the GMT value is greater then the required value. GMT is computed from the waterplane inertia and the displaced volume at the equilibrium heel angle. Ratio of GMT and heeling arm

Calculates the following ratio and the criterion is passed if the ratio exceeds the specified value. Page 311

Appendix F

GM sin( )  HA( ) Where the heel angle, , is the lesser of: a user-specified heel angle; angle of margin line immersion; angle of deck edge immersion; or first flooding angle of the specified key point type. In addition, this angle may also be multiplied by a user-specified factor. The specified cross-referenced heel arm is then evaluated at this heel angle to give: HA( ) . Finally, The transverse GM is taken at a user-specified heel angle or angle of equilibrium (without heel arm).

Ratio of GMt and heel arm criterion Value of GZ at equilibrium - general heeling arm

Calculates the value of the GZ curve at the equilibrium intersection of the GZ and heel arm curves. The criterion is passed if the GZ value is greater then the required value.

Value of GZ at equilibrium - general heeling arm Value of maximum GZ above heeling arm

Finds the maximum value of (GZ - heel arm) at or above a specified heel angle. The first downflooding angle may be selected as an upper limit. The criterion is passed if the value of (GZ - heel arm) is greater then the required value. Page 312

Appendix B

Value of maximum GZ above heeling arm

The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”. Maximum ratio of GZ to heeling arm

This criterion calculates the maximum ratio of GZ : Heeling arm (for the same heel angle) within the range of heel angles specified. The value of GZ at this heel angle must be greater than zero. If the heeling arm is zero or negative in the range, then the point with maximum positive GZ (where the heeling arm  0.0) will be selected. The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”. Examples:

Page 313

Appendix F

Upper limit is 50% of angle of margin line immersion (43 / 2 = 21.5). In the range 0 to 21.5, the maximum ratio of GZ:heel arm occurs at 21.5. At this heel angle the value of GZ is 0.553m and the heel arm 0.930m giving a ratio of 59%.

In this case a constant heeling arm is used, thus the maximum ratio occurs at the angle of maximum GZ (62.4). At this heel angle the value of GZ is 1.122m and the heel arm 0.5m giving a ratio of 224%.

Page 314

Appendix B

Finally, the downflooding angle is 94.3, at this heel angle the heel arm is zero (thus the ratio infinite). Hence the criterion is passed. The angle and value of GZ is given for the location where it is a maximum (in the region where the heel arm is zero; the exact value will depend slightly on the heel angles tested in the Large Angle Stability analysis.)

The same is true if an unusual user-defined heeling arm is used. In this case the heeling arm is zero between 50 and 70. Hence the maximum ratio reported is infinity and occurs at the angle where GZ is maximum in this heel angle range.

Page 315

Appendix F Minimum ratio of GZ to heeling arm

This criterion calculates the minimum ratio of GZ : Heeling arm (for the same heel angle) within the range of heel angles specified. And checks that this ratio is greater than a specified value. This criterion can be used to check that the GZ is at least as great as the heeling arm over the specified range. If a heeling arm with zero amplitude is used, the same criterion may be used to check that the GZ is positive over the specified range. The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”. Ratio of GZ values at phi1 and phi2 - general heeling arm

Used to check the ratio of GZ values at two points on the GZ curve. The heel arm is used to define the equilibrium angle and the heel angle where (GZ - heel arm) is maximum. The criterion is passed if the ratio is less than the required value.

GZ 1  Ratio = GZ  2  Angle of maximum GZ above heeling arm

Calculates the heel angle at which the difference between the GZ curve and the heeling arm is greatest (GZ - Heel Arm is maximum, positive). The criterion is passed if the angle is greater then the required value.

Angle of maximum GZ above heeling arm - general heeling arm Angle of equilibrium - general heeling arm

Calculates the angle of equilibrium with the specified heeling arm. The equilibrium angle is the smallest positive angle where the GZ and heeling arm curves intersect and the GZ curve has positive slope. The criterion is passed if the equilibrium angle is less then the required value.

Page 316

Appendix B

Angle of equilibrium - general heeling arm Angle of equilibrium ratio - general heeling arm

Calculates the ratio of the angle of equilibrium (with the specified heeling arm) to another, selectable angle. The angle of equilibrium is computed as described in §Angle of equilibrium general heeling arm. Ratio =

 equilibrium  specified

The other angle used to compute the ratio may be one of the following: Required angle for ratio calculation Auto complete text Marginline immersion angle MarginlineImmersionAngle Deck edge immersion angle DeckEdgeImmersionAngle Angle of first GZ peak DownfloodingAngle Angle of maximum GZ MaximumGZAngle First downflooding angle FirstGZPeakAngle Angle of vanishing stability with heel arm VanishingStabilityWithHeelArmAngle

Angle of vanishing stability - general heeling arm

Calculates the location of the first intersection of the GZ curve and heel arm curve where the slope of the GZ curve is negative. The criterion is passed if the angle is greater then the required value. This criterion should not be confused with the range of positive stability.

Page 317

Appendix F

Angle of vanishing stability - general heeling arm Range of positive stability - general heeling arm

Computes the range of positive stability with the heeling arm. [Range of stability] = [Angle of vanishing stability] – [Angle of equilibrium] The criterion is passed if the value of range of stability is greater then the required value.

Range of positive stability - general heeling arm

Page 318

Appendix B Freeboard at equilibrium - general heeling arm

Calculates the angle of equilibrium with a general heeling arm applied. The equilibrium angle is the smallest positive angle where the GZ and heeling arm curves intersect and the GZ curve has positive slope. The freeboard of the specified type of key-point or key-line at this angle of equilibrium is then found. The criterion is passed if the equilibrium angle is less then the required value. GZ area between limits type 1 - general heeling arm

Computes the area below the GZ curve and above the heel arm curve between the specified heel angles. The criterion is passed if the area is greater than the required value. 2

GZ ( )  heel arm( )d Area =  1

GZ area between limits type 1 - general heeling arm GZ area between limits type 2 - general heeling arm

The area between the GZ curve and heel arm and the area under the GZ curve is computed (Area 1). The required value is based on a constant plus a proportion of the area under the GZ curve (Area 2). The criterion is passed if the ratio is greater than the required value. 2

Area 1 =

 GZ ( )  heel arm( )d ; 1

4

Area 2 =

 GZ ( )d ; 3

Area 1  constant  kArea 2

Page 319

Appendix F

GZ area between limits type 2 - general heeling arm Ratio of areas type 1 - general heeling arm

The ratio of the area between the GZ curve and heel arm and the area under the GZ curve is computed. This criterion is based on the area ratio required by various Navies’ turning and passenger crowding criteria. Type 1 stands for which areas are being integrated to calculate the ratio (see graph). The criterion is passed if the ratio is greater than the required value. 2

Area 1 =

 GZ ( )  heel arm( )d ; 1

4

GZ ( )d Area 2 =  ; 3

Area 1 Ratio = Area 2

Page 320

Appendix B

Ratio of areas type 1 - general heeling arm Ratio of areas type 2 - general heeling arm

This criterion is used to simulate the effects of wind heeling whilst the vessel is rolling in waves. Because of the many different ways in which this criterion is used it has several options for defining the way in which the areas are calculated. If a gust ratio of greater than 1.0 is used, the vessel is assumed to roll to windward (under the action of waves with the steady wind pressure acting on it, then roll to leeward under a gust. Hence the rollback angle is taken from the equilibrium angle with the steady wind heeling arm, but the integration for Area 1 is taken from the equilibrium with the gust wind heeling arm. The roll back may be specified as either a fixed angular roll back from the angle of equilibrium with the steady wind heel arm or can be rolled back to the vessel equilibrium angle ignoring the wind heeling arms (i.e.: where the GZ curve crosses the GZ=0 axis with positive slope). Note The Large Angle Stability analysis heel angle range should include a sufficient negative range to allow for the rollback angle. For more information see: §Heel. 2

GZ ( )  gust heel arm( )d Area 1 =  1

Area 2 =

2

 gust heel arm( )  GZ ( )d 1

Area 1 Ratio = Area 2 Page 321

Appendix F

Ratio of areas type 2 - general heeling arm Ratio of areas type 3 - general heeling arm

The ratio of the area under the GZ curve to the area under the heel arm curve is computed. This criterion is based on the area ratio required by BS6349-6:1989. The criterion is passed if the ratio is greater than the required value. Areas under the GZ=0 axis are counted as negative. Area GZ =

2



GZ ( )d ;

1

Area HA =

2



heel arm( )d ;

1

Ratio =

Page 322

Area GZ Area HA

Appendix B

Ratio of areas type 3 - general heeling arm

Multiple heeling arm criteria

These criteria are used to check the effects of combinations of up to three heeling arms and their combinations, for example passenger crowding, turning, wind. The combined heeling arms are computed by adding the values of the individual heeling arms at each heel angle. Ratio of GZ values at phi1 and phi2 - multiple heeling arms

Checks the ratio of GZ values as per §Ratio of GZ values at phi1 and phi2 - general heeling arm with the specified heeling arms.

Page 323

Appendix F

Ratio of GZ values at phi1 and phi2 - multiple heeling arms Angle of equilibrium - multiple heeling arms

Checks the equilibrium heel angle as per §Angle of equilibrium - general heeling arm with the specified heeling arms.

Angle of equilibrium - multiple heeling arms GZ area between limits type 1 - multiple heeling arms

Checks the area under the heel angle as per §Freeboard at equilibrium - general heeling arm Page 324

Appendix B

Calculates the angle of equilibrium with a general heeling arm applied. The equilibrium angle is the smallest positive angle where the GZ and heeling arm curves intersect and the GZ curve has positive slope. The freeboard of the specified type of key-point or key-line at this angle of equilibrium is then found. The criterion is passed if the equilibrium angle is less then the required value. GZ area between limits type 1 - general heeling arm with the specified heeling arms.

GZ area between limits type 1 - multiple heeling arms GZ area between limits type 2 - multiple heeling arms

Checks the area under the heel angle as per §GZ area between limits type 2 - general heeling arm with the specified heeling arms. 2

GZ ( )  heel arm( )d Area 1 =  ; 1

4

GZ ( )d Area 2 =  ; 3

Area 1  constant  kArea 2

Page 325

Appendix F

GZ area between limits type 2 - general heeling arm Ratio of areas type 1 - multiple heeling arms

Checks the area under the heel angle as per §Ratio of areas type 1 - general heeling arm with the specified heeling arms.

Page 326

Appendix B

Ratio of areas type 1 - multiple heeling arms Subdivision Index s-factor - MSC_216(82)

The Subdivision Index s-factor (probablity of survival) as described in IMO MSC.216(82) is computed. Several extra options are presented to the user.

Page 327

Appendix F

Option

Description Subdivision Index s-factor – MSC.216(82)

Vessel type : Passenger, Cargo, User

The type of vessel being analysed. This is used to determine default parameters and which s-factors should be computed.

Which s-factors should be applied ?

s-Final s-Intermediate s-Moment

Lower angle of range: greater of

The largest of the seleted angles is used to define the beginning of the range. It is recommended that the vessel be heeled so that the equilibrium angle is positive, but if it is heeled in the other direction, the range can be specified to start at zero (or some other angle).

Specified heel angle

Page 328

Units

deg

Angle of equilibrium

See Nomenclature

deg

Upper angle of range: lesser of

The lowest of the selected angles can be used to specify the upper limit of the range of positive stability. The beginning of the range of positive stability is taken as the first positive equilibrium angles

first downflooding angle

See Nomenclature

deg

angle of vanishing stability

See Nomenclature

deg

Immersion angle of Marginline or DeckEdge

See Nomenclature

deg

s-Final

Parameters for computing the s-Final factor

Max. GZ limit

Upper limit of allowable maximum GZ value when computing s-Final

length

Range limit

Upper limit of allowable range of positive stability when computing sFinal

deg

K-factor min. heel

Theta_min used to determine K

deg

K-factor max. heel

Theta_max used to determine K

deg

s-Intermediate

Parameters for computing the sIntermediate factor

Max. GZ limit

Upper limit of allowable maximum GZ value when computing s-Intermediate

length

Range limit

Upper limit of allowable range of positive stability when computing s-

deg

Appendix B

Intermediate Max. allowable equilibrium heel angle

Maximum allowable equilibrium heel angle after damage. If the equilibrium heel angle exceeds this value then sIntermediate is zero.

deg

s-Moment

Parameters for computing the sMoment factor

intact displacement at subdivision draft

Displacement of the intact vessel at the subdivision draft

mass

GZ reduction

Reduction to be applied to maximum GZ

length

Passenger heel moment

Link to passenger heeling moment

mass.length

Wind heel moment

Link to wind heeling moment

mass.length

Select survival craft heel moment

Link to heeling moment that defines the effect of launching survival craft

mass.length

Angle of equilibrium must be less than immersion angle of ...

There are two rows where you can check that the equilibrium angle is less than the immersion angle of different key points (for example PotentialDownfloodingPoints and DeckEdge). This is to check compliance with MSC.216(82) Regulation 7-2 5.2 and 5.3

deg

Shall be greater than / Shall not be less than

Permissible minimum value for sfactor

Vessel type: If Passenger is selected, then s-Intermediate and s-Moment factors are computed. For the s-Final factor, the minimum and maximum heel angles are set to 7 and 15 deg. respectively. The criterion result is then the minimum value of s-Intermediate and (s-Final * s-Moment). If Cargo is selected, then only the s-Final factor is computed and in this case, the minimum and maximum heel angles are set to 25 and 30 deg. respectively. If User is selected, then all three s-factors are computed as for the Passenger ship, and any values for the s-Final factor minimum and maximum heel angles may be specified. s-Final = K. {GZmax / limitGZmax . Range / limitRange}1/4 where: K = 1 if equilibrium heel = Theta_max K = {(Theta_max – equilibrium heel) / (Theta_max – Theta_min)}1/2 s-Intermediate = {GZmax / limitGZmax . Range / limitRange}1/4 if equilibrium heel > Max. allowable equilibrium heel angle then s-Intermediate = 0 s-Moment = (GZmax – GZ reduction) . Displacement / Mheel where: Mheel is the maximum of the three selected heeling moments. The result is the minimum of s-Intermediate and (s-Final * s-Moment). Page 329

Appendix F

All s-factors are in the range 0