Bulk Carrier

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I S S I O N The mission of the American Bureau of Shipping is to serve the public interest as well as the needs of our clients by promoting the security of life, property and the natural environment primarily through the development and verification of standards for the design, construction and operational maintenance of marinerelated facilities.

quality & environmental P O L I C Y It is the policy of the American Bureau of Shipping to be responsive to the individual and collective needs of our clients as well as those of the public at large, to provide quality services in support of our mission, and to provide our services consistent with international standards developed to avoid, reduce or control pollution to the environment. All of our client commitments, supporting actions, and services delivered must be recognized as expressions of Quality. We pledge to monitor our performance as an on-going activity and to strive for continuous improvement. We commit to operate consistent with applicable environmental legislation and regulations and to provide a framework for establishing and reviewing environmental objectives and targets.

Executive Summary Bulk carrier safety initiatives have received a new sense of urgency, accompanied with a greater sense of liability in the marine industry. The relationship of bulk carrier age to total loss of a vessel cannot be ignored, but other operational considerations also play an important role in maintaining the structural integrity. Statistically, for conventional bulk carriers, those vessels with more than 20 years of operation have a greater total loss probability, in addition to a greater loss of life probability. Capesize (more than 80k dwt) and handysize (10 to 40k dwt) vessels account for the majority of losses at sea. This is a concern as 51 percent of the handysize fleet is 20 years old or greater. There are many operational considerations contributing to the loss of a vessel that must be addressed for the next generation of bulk carriers. ABS SafeHull is the starting point for an ABS approved design. Application of the principles found in ABS SafeHull provide the cornerstone to a structurally sound vessel. Additionally, the ABS SafeShip program follows a vessel from inception through its service life. This information management system allows owners the best method for maintaining their vessels. For further design verification, several analytical tools exist to address unique considerations for the larger bulk carrier designs. Design alternatives to the conventional single sided vessels have been proven in the market to bring added strength, including the double hull or double side skin design. Bulk carriers with double sides are more durable ships – bringing added benefits for safety and operations. ABS is a classification society of choice for bulk carriers. With practical experience and unmatched technical capability, ABS offers shipowners and shipbuilders of these vessels the most comprehensive classification services available.

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Table of Contents INTRODUCTION .....................................................................................................................3 ABS’ STRONG POSITION .......................................................................................................4 MARKET SHARE ..............................................................................................................................................4 RECENT ACTIVITY - DOUBLE SIDE SKIN BULK CARRIERS ...................................................................................4 BULK CARRIER LOSSES.........................................................................................................5 OPERATIONAL CONSIDERATIONS ........................................................................................8 HOLD SIDE FRAME PROBLEMS .........................................................................................................................8 Fatigue ..........................................................................................................................................................8 Corrosion ......................................................................................................................................................9 Damage.......................................................................................................................................................10 GREEN WATER .............................................................................................................................................11 SPONTANEOUS COMBUSTION .........................................................................................................................11 IMPROVING BULK CARRIER SAFETY..................................................................................12 APPLICATION OF ABS SAFESHIP ....................................................................................................................12 APPLICATION OF ABS SAFEHULL ...................................................................................................................12 Bulk Carrier Designs ..................................................................................................................................13 Side Frames ................................................................................................................................................13 Cross Deck Structures .................................................................................................................................14 Corrugated Transverse Bulkheads...............................................................................................................14 TAIL SHAFT BEARING PERFORMANCE .............................................................................................................15 PERMANENT ACCESS FOR SURVEY ..................................................................................................................15 DESIGN ALTERNATIVES ......................................................................................................16 DOUBLE SIDE SKIN BULK CARRIERS ...............................................................................................................16 PARAMETRIC STUDY: DOUBLE SIDE SKIN BULK CARRIERS.................................................................................17 Longitudinal Framing .................................................................................................................................18 Transverse Framing ....................................................................................................................................18 Double Side Space.......................................................................................................................................18 Ship Configurations ....................................................................................................................................18 Operating Costs ..........................................................................................................................................20 HYCON BULK CARRIERS ................................................................................................................................21 APPENDIX 1 DOUBLE SIDE SKIN BULK CARRIERS TO ABS CLASS.........................................................................................22 APPENDIX 2 WEIGHING THE OPTIONS ..............................................................................................................................24

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Introduction In selecting the most appropriate classification society for a new construction project, the client should consider the following: ABS’ strong position in bulk carrier classification comes from years of experience, backed by advanced technical programs that address the needs of the industry, including shipowners and shipbuilders. ABS stands out as a technology leader committed to continual research and the development of appropriate Rules and Regulations governing the design parameters and vessel life. ABS surveyors’ experience is further enhanced by a commitment to technology and the analytical programs offered by the engineering department. By responding to clients’ needs through a worldwide network of offices, clients receive the necessary attention to ensure project success. ABS has programs already in place and personnel with the needed experience to aid in the design and construction of the next generation of bulk carriers. ABS currently has projects for both the latest Dunkerque-max bulk carriers and double side skin (DSS) bulk carriers. ABS has the technology and practical experience necessary to meet the design challenges posed by these vessels.

Classification with ABS Includes: • The most authoritative and appropriate Rules for the classification of bulk carriers. • Design review to verify the design complies with the ABS Rule requirements. • Surveys during construction to assure compliance with classification requirements, as given in the Rules and on the ABS approved plans, and attendance on board during official sea trials. • Governmental authorizations to issue certificates and/or conduct surveys pertaining to the Load Line, MARPOL, SOLAS, tonnage conventions, and ISM Code. • Acceptance by the ABS Classification Committee and award of the appropriate notation. • Performance of periodic surveys to assure that the vessel is maintained to class standards.

The Benefits of Classing with ABS Include: • • • • • • •

Knowledge that the vessel is appropriate for the intended service. Backing of years of relevant knowledge and experience. Single source for all technical needs. Indication of due diligence of owner/operator. Compliance with governmental requirements. Indication of performance of proper maintenance. Assurance of protection of capital investment.

Based on extensive and varied experience, ABS provides comprehensive classification services fulfilling client needs for any bulk carrier project, whether single or double sided.

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ABS’ Strong Position Market Share At the beginning of 2002, the ABS bulk carrier fleet had 13 percent market share of existing vessels and 17 percent of vessels on order.1 ABS is well-equipped with proven experience and the technical tools necessary to meet today’s market demand and provide for future project success. The ABS fleet at year-end 2001, contained 737 bulk carriers, aggregating 22.8m gt. Recent contracts include the construction of new DSS bulk carriers of 51,000 dwt in China. By year-end 2001, ABS had a total of 65 bulk carriers aggregating 2.3m gt on its orderbook from owners worldwide. Experienced operators recognize ABS’ technical excellence and choose ABS for their classification needs. Currently there are over 5,800 vessels in the dry bulk carrier fleet. Of these vessels, some 119 (2 percent) are DSS bulk carriers.2

Recent Activity - Double Side Skin Bulk Carriers ABS partnered with two different owners on the construction of DSS bulk carriers in 1996. Top Glory and Hong Kong Ming Wah Shipping Company partnered with Oshima Shipyard in Japan for their handymax bulk carriers. DSS bulk carriers are also being built to ABS Class in China and Taiwan. In January 1997, Oshima Shipyard in Japan delivered the 48,000 dwt Pacific Scorpio to Hong Kong Ming Wah Shipping Company. This vessel was the last in the series of six vessels. The Scorpio marked a double milestone for the bulk shipping industry: completion of the first significant order by a major shipowner for double sided bulk carriers, and also a first for the SafeHullbuilt bulk carriers. The order was originally placed with the conviction that such a vessel would provide simplified maintenance and operation, increased efficiency in loading and unloading, and enhanced structural safety. Additionally, these vessels are expected to pay back the increased steel and construction costs in less than half their service life. These vessels represent a step forward in longevity and safety and represent cumulative benefits for their owners.

____________________________ 1 Source: LLP Seaway, gt based 2 Source: LLP Seaway, Jan 2002

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Bulk Carrier Losses Tragic losses from bulk carrier casualties led many in the marine industry, including ABS, to investigate what design modifications could be made to promote bulk carrier safety and deter further losses. Bulk carriers are built to transport various dry cargoes. The most common are grain, iron ore and coal. In the 1960s there were various problems associated with the transportation of grain that were addressed after a series of accidents involving these types of vessels. Requirements for the safe carriage of iron ore and other high-density cargoes were enhanced in 1997 with the introduction of structural survivability criteria and continue to be under scrutiny today. Primary barriers to resist flooding of a single skin side (SSS) bulk carrier vessel include: • Hatch covers and foredeck fittings • Side shell plating with attached supporting side frames Once the foremost hold floods, a ship will likely suffer a total loss and by some estimates, the number one cargo hold flooding accounts for about 40 percent of casualties for bulk carriers. Three areas of the hull structure have been identified as main areas of concern from past casualties. These are the: • Hold frames and brackets • Corrugated bulkhead • Cross deck structure Over the time period 1982 to 2001, hull damage leading to sinking of conventional bulk carriers accounts for some 72 reported losses. During the same time period, there was one recorded DSS bulk carrier lost. Cracked or damaged side shell is the leading cause of bulk carrier losses. This data has been substantiated by a study conducted for the International Maritime Organization (IMO) and submitted to the Maritime Safety Committee (MSC) by the United Kingdom in March 2002. This study confirmed that for any size bulk carrier, side shell damage dominates recorded losses. By comparison, there are much fewer losses attributable to hatch cover failure.

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These charts depict that side shell failures are the most likely reason for loss and are more likely to occur to the panamax and capesize bulk carriers that are more than 20 years old.

This chart illustrates the area of the initiating event for a recorded incident leading to total loss. Side shell damage can have a dramatic and sometimes unseen effect on the structural soundness of a bulk carrier.

This chart gives the probability for each type of initiating event, across the various vessel types. Here it depicts that the larger bulk carriers, capesize and panamax, have a higher likelihood of loss. 6 • Bulk Carrier Solutions: Safer and Stronger Vessels

Age is a contributing factor in the loss of bulk carriers. Statistically, bulk carriers 20 years and older exhibit a greater chance of total loss than their younger counterparts. Intercargo notes that the actual number of ships and lives lost has fluctuated each year, while the average age profile of lost bulk carriers has remained at around 20 years.3

Many operational factors contribute to the structural soundness of a vessel. These issues must be addressed to ensure that safe operation is maintained and casualties are reduced.

____________________________ 3 Bulk Carrier Casualty Report, 2001 and the Previous Ten Years (1992-2001), Intercargo

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Operational Considerations For the safe operation of a bulk carrier there are many facets that must be identified and considered. The majority of structural problems associated with bulk carriers arise with the side shell. Other issues to address include the effects of green water on deck.

Hold Side Frame Problems For conventional bulk carriers, the cargo hold side frames and brackets can be considered the weakest link in the structure of the vessel. These elements are subject to fatigue, corrosion, and mechanical damage during loading and unloading. The International Association of Classification Societies (IACS) first responded to these problems in 1993 when it introduced the Enhanced Survey Program (ESP), in an attempt to identify and correct degradation through corrosion, fatigue, and hard wear and tear. Casualty studies in the mid-1990s also focused on the foremost cargo hold.

Fatigue Bulk carriers are susceptible to many modes of cyclic forces that combine with other forces acting upon the vessel’s structure. Over time these cyclic stresses, can seriously weaken the vessel’s structural capacity. Three areas on a bulk carrier that are especially prone to fatigue are the hold side frames, the side longitudinals in the upper and lower wing tanks, and the toes of the hatch coaming termination brackets. Cyclic wave pressure acts upon the side frames of the vessel in a constant cycle of loading and unloading forces. For bulk carriers carrying high density cargo, such as iron ore, the side frames do not have an internal pressure to counteract the external forces and the side shell is forced inward by the unbalanced forces. This can result in a weakening of the side frame. Conversely, internal pressures created by lower density cargo impose loads in the opposite direction when a wave trough is encountered. This occurs when the cargo fills the cargo holds and pushes out on the side frame structure. This pressure can also fluctuate and react with the motions of the vessel. Additional fatigue loads on the side frames arise from hull girder shear forces. Bulk carriers with cargo loaded in an alternate hold pattern experience high levels of still water shear forces as the weight of the holds loaded with the cargo are pushing down and the buoyant forces are pushing up the empty holds. These upward and downward acting still water forces combine with the shear forces that fluctuate with the wave motions to impose fluctuating stresses on the side frames.

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Similarly, the longitudinal framing of the upper and lower wing tanks is subjected to fluctuating stresses due to the external wave action as well as the internal pressure from the ballast tanks. These longitudinals are also subjected to the fluctuating longitudinal hull girder stresses imposed by the passing wave along the length of the vessel. The toes of the hatch coaming termination brackets are subjected to the fluctuating longitudinal hull girder stresses as well as the torsional wave induced stresses imposed by waves encountered at oblique wave headings.

Corrosion Certain products, including coal, phosphates and raw sulfur, transported by bulk carriers can rapidly corrode the hold side frames and promote fractures. For a capesize bulk carrier carrying coal and iron ore it has been recorded that a hull web frame, with an original thickness of 10 mm can corrode to only 3 to 5 mm along the bottom portion of the hold in a short period. Additionally, the hold frame does not corrode evenly along the vertical length of the frame.

POSITION

AREA OF PITTING CORROSION

WEB THICKNESS

Upper

Few

10 mm

Upper

>50 percent

7 – 9 mm

Middle

>100 percent

5 – 8 mm

Bottom

100 percent

3 – 5 mm

*due to carriage of coal and iron ore The corrosive nature of coal is due to its sulfur content. This occurs as condensation in the cargo hold of the vessel reacts with coal to produce a diluted solution of sulfuric acid, which over time corrodes supporting structures and frames. Corrosion increases the structure’s susceptibility to fatigue and buckling, and lessens the structural integrity of the vessel, as the web thickness is not sufficient to support the heavy cargo being transported. As a result, the frame can detach from the side shell.

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Damage Side shell problems are prevalent in all sizes of bulk carriers, although there is a higher occurrence for the larger panamax and capesize bulk carriers.

For high-density cargoes the speed of loading may cause damage to the ship’s structure. Any time the vessel is loaded in an asymmetrical manner, in relation to the central axis, the ship will twist. This will create other stresses within the hull structure. These stresses can have a damaging effect on the hull, even in still water conditions. It is known that the dense nature of iron ore, about 3 tons per cubic meter, generates large stresses on a ship’s structure. Loading this cargo must be carefully controlled to not exceed allowable stresses. The risk associated with improper cargo loading can be greatly magnified once the vessel encounters the dynamic forces due to wave action. Additionally, careless maneuvering of equipment used by terminals can cause accidental damage to bulk carriers transporting grains, ore and coal. Loading and unloading practices have a very real effect upon the vessel’s operational life span that can ultimately lead to damage or loss of the side shell plating. The practice of dislodging cargo from side shell frames with jackhammers, removing ore with multi-ton claws, or loading minerals at high rates without considering the physical effect on the ship are common occurrences. Certain types of bulk cargoes require bulldozers to move cargo during unloading, with inevitable damage to frames, bulkheads and plating. Additionally, the concentrated weight distribution of Photo credit: International Dry Bulk Terminals Contact Group (DBTG) lower profile cargoes require special attention. Scrap metal, for example, must be handled carefully to prevent damage to the bottom plating of the hold. Steel coils, if not properly secured, with their large weight concentration may shift during voyage and damage the hull.

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These ocurences may cause unseen damage that is manifested over the operational life of the vessel. This can include structural cracks and detached side shell frames. This damage to the vessel hull only accentuates the fatigue and corrosion affects. Side shell deficiencies account for the majority of the bulk carrier losses. The loss of the side shell plating may result in the total loss of the vessel.

Green Water The flooding of spaces below the main deck due to hatch cover or securing device failure, or failure of other deck fittings, has been linked to green water loads. Failures have been attributed both to direct impact loads of an impinging wave, and to impact by loose gear, deck equipment or fittings that have broken away from their foundations and then been carried by green water. Design options to provide increased reserve buoyancy above the main deck and added bow protection against green sea loads are currently being analyzed to reduce the occurrence and effects of green water on deck. Based on the formal investigation report on the loss of the Derbyshire, new model tests and extreme value predictions for severe wave conditions have been carried out and are being used to reassess strength requirements for hatch covers and foredeck fittings. Preliminary assessment of these model test results indicate that current IACS unified strength requirements for hatch covers are adequate for ships in the intact condition, but that further assessment and refinement may be in order to account for greater forward green water loads if the foremost cargo hold or forepeak spaces were to flood. Work is also proceeding within IACS to evaluate the capacity of foredeck fittings and equipment attachments at the deck to resist the lateral loads of boarding green seas.

Spontaneous Combustion Additional problems arise in the transportation of coal, which may emit combustible methane gas. Spontaneous combustion may also occur in certain types of coal that are self-heating. Even with the transportation of fishmeal there is a need for special consideration as it too can spontaneously combust.

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Improving Bulk Carrier Safety ABS programs to improve bulk carrier safety not only monitor the vessel through its entire life cycle, but also identify the loads that act upon the vessel and the verify the design against corrosion and fatigue. Additionally, ABS has programs available to evaluate the other aspects of vessel operation. Intercargo also reports that recent rules seem to be having a positive effect.4 Changes that will allow for permanent survey access are a further effort to improve the safe operation of bulk carriers.

Application of ABS SafeShip The ABS SafeShip program starts in the design office with the application of the proven power of ABS SafeHull, recognized as the most rational, dynamically based system available for evaluating the design of a bulk carrier. As the vessel takes shape in the shipyard, construction conforms to the superior requirements of the ABS SafeHull Construction Monitoring Program. On delivery, a structural database is created utilizing ABS SafeNet Hull Maintenance. Specified as-built drawings are entered into the ABS SafeNet Vessel Drawings system, providing life-cycle storage and easy updating of this crucial information. In service, the unique technical and commercial capabilities of the ABS SafeNet Hull Maintenance, Maintenance & Repair, and Survey Status modules are used to manage the structural and mechanical condition of the vessel. Significant cost savings flow from improved performance, less down time, greater operating efficiencies and reduced exposure to risk. Free enrollment in the ABS SafeShip program is open to all new and existing vessels designed to meet ABS SafeHull criteria.

Application of ABS SafeHull ABS SafeHull is ideal for identifying the loads and failure modes that need to be considered for a bulk carrier. The ABS SafeHull System was conceived as a complete technical resource comprising criteria based on design and structural evaluation, as well as a comprehensive suite of software applications programs, technical support services, and related technical documentation and guidance. The SafeHull criteria has been developed, based on extensive research and analysis, with a view to improving the performance of problematic structural areas in bulk carrier designs. Other critical areas, such as the supporting structures in the upper wing tanks and forebody structures, have also been addressed in the criteria. ____________________________ 4 Bulk Carrier Casualty Report, 2001 and the Previous Ten Years (1992-2001), Intercargo 12 • Bulk Carrier Solutions: Safer and Stronger Vessels

SafeHull Design Cycle This system is divided into two parts. During the design process, or Phase A, the general arrangement passes through a refining process beginning with an automated generation of the Hull Configuration. Next, calculations determining the dynamic loads assess the reaction of the designed vessel against specific criteria. This is followed by a determination of the structural components, compliance with strength criteria and fatigue assessment. Evaluation of the design is the next step in the process. Commonly referred to as Phase B, this stage generates a Finite Element Model (FEM) that again runs through a calculation of dynamic loads. Following 3-D Global Finite Element Analysis, the design runs through an assessment of Failure Modes to confirm its structural integrity. This process verifies a design with a lifetime performance able to withstand all relevant failure modes. For bulk carriers, torsional strength of the hull is of concern due to large hatch openings. Attention is also given to the effects of loading two adjacent holds – known as block loading, as well as the strength of ballast holds. These conditions are explicitly covered in the load cases for structural analysis.

Bulk Carrier Designs Typical bulk carrier designs represent a compromise between operational demands and structural requirements. Consequently, the margins of safety of different structural components are not uniform. Of main concern are the lack of structural redundancy and inadequate support in the transverse direction. In addition, the rigid double bottom structure and large upper wing tanks are much stiffer than the side frames and cross deck structure.

Side Frames Side frames are one of the weakest links in a bulk carrier structure. These vertical frames on the side shell connect two highly rigid structures, the double bottom/lower wing tank and upper wing tank. Side frames in dry cargo holds experience maximum stresses when alternate holds are loaded with high-density cargo and the ship is fully loaded. The low cargo profile causes side frames in these holds to experience greater flexure due to the large external pressures that are not counteracted by internal cargo pressures. The flexing is further magnified by the rotation of the rigid lower wing tank caused by the large downward force of the high-density cargo acting on

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the double bottom. All these effects contribute to reducing the fatigue life of the connecting brackets of the side frames, sometimes causing their detachment from the side shell.

Cross Deck Structures In the past, minimal attention was paid to the strength of cross deck structures, because they were not considered significant to the strength of the hull girder. Because of frequent occurrences of buckling in these areas, more attention is now directed to the design of cross deck structures. Three kinds of buckling problems can occur in these structures. First, in the case of block loading (a load condition in which two adjacent holds are loaded with heavy cargo), large transverse bending (sagging) can occur in the transverse bulkhead, causing high compressive forces and stresses in the cross deck structures. The static and dynamic external pressures further magnify the compressive stress. A second buckling problem occurs in oblique wave conditions, where wave-induced torsion creates shearing forces in the longitudinal direction of the cross deck, which can result in shear buckling of the cross deck plating. Thirdly, lateral bending in the cross deck from shearing forces can result in buckling of the hatch corners. The buckling problems become more pronounced in wide bulk carriers with large cargo holds, since wave-induced torsion is a function of the breadth of the ship.

Corrugated Transverse Bulkheads Corrugated transverse bulkheads, especially those in dry cargo holds, are also considered critical in a bulk carrier structure. Prior to 1997, the SOLAS Convention assumed that watertight transverse bulkheads were able to prevent progressive flooding if the hold was accidentally flooded. Nominal hydrostatic loads, which do not necessarily represent the actual dynamic loads in a damaged condition, were applied. The 1997 amendments to SOLAS recognized that the collapse of corrugated bulkheads after side structure failure, and subsequent progressive flooding, might be one of the primary causes for bulk carrier losses. This weakness was identified by ABS in 1994 during the development of SafeHull criteria for bulk carriers, when evaluating the effects of loads in a simulated flooded condition, with estimated equilibrium waterline and static and dynamic loads (including sloshing) of sea water in the flooded hold. IACS Unified Requirements now address this known weakness. The strength formulation for corrugated bulkheads was developed based on the results of a series of 3-D finite element analyses of corrugated bulkheads. The vertical bending moment acting on the transverse bulkhead is a function of torsional rigidity of the upper and lower stools, the stiffness of the double bottom structures, and the loading in the hold. The ultimate strength of corrugated bulkheads is examined to prevent catastrophic failure in the event of accidental hold flooding. The criteria also address in an explicit manner other critical areas, such as: • fore-end strengthening against slamming: • transverse webs in the upper and lower wing tanks, in way of the ballast hold; • double bottom structures for alternate hold loading conditions; • transition zones between the fore peak and Number 1 cargo hold; and • operational wear and tear, primarily of inner bottom plate and side frame connections. 14 • Bulk Carrier Solutions: Safer and Stronger Vessels

Tail Shaft Bearing Performance For the larger bulk carriers driven by high-powered diesel engines there is the potential for tail shaft bearing problems if careful attention is not paid to the propulsion shafting alignment during the design and construction of the vessel. The issue is of particular importance in the design of bulk carriers where the extremely high bhp of the engine results in very stiff, large diameter shafting. The ABS SHAFT software can be used to analyze shaft alignment and evaluate tail shaft bearing condition using deflection data derived from the finite element modeling of the hull structure. ABS SHAFT takes into account hull flexibility as well as permitting the evaluation of the condition of the tail shaft bearing. This program is intended for the design/evaluation stage of the vessel’s life, but it can also be used to trouble-shoot existing installations.

Permanent Access for Survey SOLAS Regulation has been drafted requiring ballast tanks and cargo holds of bulk carriers greater than 20,000 gt, constructed on or after 1 January 2005 to be provided with a permanent means of access to enable, throughout the life of a ship, overall and close-up inspections and thickness measurements of the ship’s structures to be carried out by the flag Administration and ship’s personnel. The means of access are to be described in a Ship Structure Access Manual approved by the Administration, an updated copy of which is to be kept on board. Of particular importance are the following means of permanent access: • Vertical access to a minimum of 25 percent of the total number of hold frames port and starboard equally distributed throughout the hold including at each end in way of transverse bulkheads, with no less that three means of vertical access fitted port and starboard. • Three means of access fitted at both ends of sides of the cross deck and in the vicinity of the centerline. Each access is to be accessible from the cargo hold or directly from the main deck. Alternatively, if the height of the overhead structure of the cross deck is less than 16m, a movable means of access (e.g., hydraulic arms with a stable base or wire lift platform) may be accepted. • One longitudinal, continuous access is to be provided for the full length of each top side and bottom hopper tank, if 6m in height, fitted adjacent to side shell with vertical access ladders to the main deck access. Portable ladders may be used for Source: IACS document, IMO DE 45, March 2002 such tanks with a height less than 6m. Bulk Carrier Solutions: Safer and Stronger Vessels • 15

Design Alternatives Tragic losses from bulk carrier casualties led many in the marine industry, including ABS, to investigate what design modifications could be made to reduce the risk of further losses. Double side skin bulk carriers, and modifications thereon, are being built to counteract some of the problems associated with single side bulk carriers.

Double Side Skin Bulk Carriers The double hull principle is not new to the marine industry. Tankers are being built with a double hull to reduce the risk of oil spills after collisions and grounding. For bulk carriers, the motivation is to protect the primary structural members against cargo-related corrosion and mechanical damage, as well as providing a barrier against extensive flooding due to low-impact side shell damage. To date there has not been a reported loss of a purpose built DSS bulk carrier with a size greater than 20k dwt. One DSS vessel of 20k dwt was lost at sea after 23 years of operation. On average, a DSS bulk carrier is scrapped after 27 years of service. DSS bulk carriers have improved structural integrity by: • Eliminating exposed, damage-prone transverse framing and their end attachment • Protecting against cargo-related corrosion and mechanical damage • Allowing better quality surface preparation and coating application – both initially and carrying out repairs • Creating much stiffer side structures effectively eliminating the flexing or fatiguing of side frame structures in conventional designs With the addition of a double side, improvements are made to the operation of bulk carriers. The time required for cargo discharge is decreased. For coal, on average, this translates to 10 percent higher daily discharge rate when compared to ships with conventional hold configuration.

Side Shell Side Frames

16 • Bulk Carrier Solutions: Safer and Stronger Vessels

Double Hull

Because of the smooth hold sides, the damage per ton of cargo discharged can be six times lower than the average in conventional bulk carriers. DSS smooth holds also save time and costs in hold cleaning and protect the cargo against external temperature variations.

Significant savings and economic advantages can be realized through an increase in structural strength. The DSS design not only eliminates exposed damageprone side frames, but also reduces the risk of hold flooding and possible sinking; especially for smaller size bulk carriers with fewer compartments. On the other hand, if the double side space were used as a ballast tank it would require closer attention. The construction cost differential for a DSS bulk carrier is nominal, and higher resale values may be realized. Additionally, the operational advantages translate into economic advantages as the speed of cargo discharge has been improved, time and cost is saved in hold cleaning, and less down time is required for repairs.

Parametric Study: Double Side Skin Bulk Carriers In 1999 ABS conducted a study to determine the structural design and operating costs of DSS bulk carrier designs. The study focused on the: • Selection of the most suitable width of the DSS structure • Identification of the type of DSS framing system • Determination of the newly formed side space (ballast vs. void) • Scantlings/steel weight of DSS vs. SSS comparison based on SafeHull requirements • Construction cost of DSS • Estimation of annual operating cost In determining the ideal width of the double side space, ABS used current IMO regulations on access openings – 600x600 (horizontal) and 600x800 (vertical). The space should provide sufficient width for safe access and inspection. The ABS Rules and SOLAS mandate that 1000mm be the minimum width; however, the ABS study increased the width to 1400 mm for capesize and handymax, and 1200 mm for panamax to provide adequate space for inspection and maintenance, as well as provide the space needed for adequately sized structural frame members. Additionally, the type of double hull framing could be either longitudinal or transverse. In either case, the horizontal stringers and vertical webs in the double side space are required for strength and safe access.

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Longitudinal Framing Longitudinal framing in bulk carriers poses additional design concerns that result in increased fatigue. In the longitudinal framing in the double side space system, the horizontal stringer has no impact on longitudinal framing scantlings. The web framing in the double side space could be every third or sixth frame spacing, and fatigue would be a factor in wider frame spacing. In a longitudinal framing system, side pressure is transmitted to the vertical web or the transverse bulkhead. Additionally side pressure loads can cause high shear forces in the webs. Careful consideration needs to be made for this high shear force.

Transverse Framing Transverse framing is preferred for a variety of reasons. One advantage is that the web frame location is flexible. Additionally, greater buckling strength is found in the side shell plating as it is subject to large vertical direction compressive loads. The web frames support the local scantling requirement, and the side pressure loads go directly to the upper and lower hopper tanks – eliminating the high shear problem encountered by the longitudinal system. The ABS study considers a transverse framing system.

Double Side Space For the DSS bulk carrier there is an additional consideration of the space created by the design. If it is used as ballast space it will require high quality internal coating. There is an added cost for maintenance, and the double side spaces cannot replace the designated ballast cargo, owing to volume and strength considersations. However, if it is left as a void space there is no need for a high quality internal coating. The ABS study considers it as a void space.

Ship Configurations The ABS study compares DSS and SSS for three typical sizes of bulk carriers: capesize, panamax and handymax. These ships were selected to establish a baseline reference in each of these respective size ranges against which DSS bulk carriers of identical deadweight, cubic capacity and speed would be compared with SSS bulk carriers.

Typical Ship Size of Single Side Bulk Carriers SHIP TYPE

SIZE (DWT)

L.B.P. (M)

BREADTH (M)

DEPTH (M)

DESIGN DRAFT (M)

Capesize

150,000

264.00

45.00

23.20

16.90

Panamax

60,000

212.00

32.24

17.80

12.40

Handymax

45,000

180.00

32.00

15.80

10.50

To provide the DSS ships with a cubic capacity equal to that of the single side equivalent, the depth of the DSS ships were increased to compensate for the loss of cargo capacity due to the double sides. The depths of the capesize, panamax and handymax double sided ships were increased by 0.6m, 0.7m and 1.11, respectively. The length and breadth remained the same.

18 • Bulk Carrier Solutions: Safer and Stronger Vessels

Although larger vessels are now the norm in bulk carrier new construction, the steel weight increase and economic findings can be used as indicators in understanding the difference between single sided and double sided bulk carriers.

Comparing a typical SSS and DSS capesize vessel, there is a weight increase in the cargo block of 419 tons for the DSS bulk carrier. This can be broken down into the various sections in the table below. REGION

DSS WEIGHT TONS

SSS WEIGHT TONS

DIFFERENCE TONS

Longitudinal Members

8,834

8,585

249

Web Frames

1,831

1,640

191

590

634

-44

W. T. BHD

1,416

1,452

-36

D. T. BHD

588

550

38

Hatch Coamings

170

170

0

Cross Deck

360

360

0

Bilge Keel

10

10

0

Phase B Increase

283

262

21

14,082

13,663

419

Trans. Hold Frames

TOTAL *For a capesize vessel of 150,000 dwt

Bulk Carrier Solutions: Safer and Stronger Vessels • 19

By adding the steel necessary beyond the cargo block region, the total structural weight difference of a typical DSS capesize bulk carrier would be 484 tons. TOTAL STRUCTURAL WEIGHT OF EACH SHIP (TONS)

DIFFERENCE (TONS)

Double Hull

Single Side

Cargo Block Weight

14,082

13,663

+ 419

Total Weight

17,377

16,893

+ 484

*For a capesize vessel of 150,000 dwt

The addition of this steel also adds to the construction costs.

DIFFERENCE (tons)

CONSTRUCTION COST DIFFERENCE

SSS capesize

TOTAL STEEL WEIGHT 16,893

DSS capesize

17,377

484

$484,000

*Note: the construction cost is based on $1000 per ton steel (average between Japan and Korea)

Operating Costs In the study, it was determined that the operating cost difference is small. Although there will be some revenue loss due to port draft restrictions requiring the carriage of less cargo.

ANNUAL COST DIFFERENTIAL CONVENTIONAL VS. DSS DESIGN Capesize

Panamax

Handymax

$10,000

$13,200

$11,800

Canal Tolls

$1,300

$8,600

$11,500

Fuel Cost

$6,700

$4,700

$5,100

(9)

(13)

(11)

days at sea

(297)

(264)

(301)

days at port

(35)

(72)

(48)

Cargo Hold Maintenance

-$22,300

-$10,400

-$5,600

Cargo Hold Cleaning

-$22,500

-$18,000

-$12,000

H & M Insurance Cost

$11,400

$8,900

$5,800

$5,700

$3,700

$4,900

-$9,700

$10,700

$21,500

Port Charges

# of total voyages

P & I Insurance Cost TOTAL ANNUAL COST DIFFERENTIAL (-) Cost savings for DSS design in 1997 USD

20 • Bulk Carrier Solutions: Safer and Stronger Vessels

The operating cost savings for a capesize DSS bulk carrier adds up to a total of $194,000 (USD) over a 20-year period. Capesize Cost Differential Initial Cost Differential

= $484,000

Operating Difference

= -$194,000

(-$9,700 per year for 20 years) Total Cost Differential

= $290,000

COST DIFFERENTIAL Net Present Value (@ 6 %)

= $373,000

*Note: 1997 USD value

Overall, a DSS bulk carrier offers added structural strength and operational advantages over the conventional SSS bulk carrier, which may eventually translate into economic benefits. The “offhire” risk of DSS bulk carriers is reduced with better maintenance and efficient operation, resulting in better availability. Repair and maintenance costs can be reduced due to the smooth-side inner hull and protected structural members located in the double side compartment spaces. Owners of DSS bulk carriers can also expect a better resale value for vessels that have had the appropriate repairs and fewer damages.

Hycon Bulk Carriers Hybrid Configuration (Hycon) Bulk Carriers are being built with double sides in the fore and aftermost holds in a shipyard in Japan. The concept of the Hycon Bulk Carrier evolved with the increased structural integrity demands from IACS in 1999 that addressed flooding of holds of SSS construction. The weight of the extra steel used for the inner skin in the fore and afts holds is offset as no extra steel is needed for the deck. Additionally, protection has been added where the wave action is the most severe. The structural safety of the hybrid design brings structural stiffness by reducing flexing and fatigue from wave loads at the fore end of the side structure. This double side also reduces the risk of hold flooding should the side structure fail.

Bulk Carrier Solutions: Safer and Stronger Vessels • 21

Appendix 1 Double Side Skin Bulk Carriers to ABS Class ABS Classification Activity – sample of DSS Bulk Carriers built 1995 to 2002.

Oshima Shipyard - Japan Pacific Acadian, Pacific Dolphin, Pacific Emerald, Pacific Mercury, Pacific Primate, Pacific Scorpio 48,400 dwt Owner - Hong Kong Ming Wah Built: 1995 to 1997 to SafeHull standards

Pacific Dolphin

CSBC Shipyard - Taiwan China Steel Trader, China Steel Investor 154,600 dwt Owner - China Steel Express Built: 1997 to SafeHull standards

China Steel Trader

Oshima Shipyard - Japan Top Sugar, Top Pioneer, Top Progress, Top Explore, Top Reliance 29,600 dwt Owner - Top Glory Built: 1998 to 1999 to SafeHull standards

Top Progress

22 • Bulk Carrier Solutions: Safer and Stronger Vessels

Oshima Shipyard - Japan Top Leader, Top Knight, Top Beauty, Top Vigour 73,600 dwt Owner - Top Glory Built: 1999 to SafeHull standards

Top Leader

New Century (formerly Jing Jiang) Shipyard - China Clipper Galaxy 51,000 dwt Owner - Galaxy Shipping Built: 2002 to SafeHull standards

Bulk Carrier Solutions: Safer and Stronger Vessels • 23

Appendix 2 Weighing the Options There are pros and cons to be considered for an informed decision to be made regarding DSS and SSS bulk carriers.

DSS Bulk Carriers

SSS Bulk Carriers

Pros: • Safer in structure • Flexible in operation

Pros: • Commercially competitive

Cons: • Loss of grain capacity (for handymax vessels)

Cons: • Vulnerable to side structure failure • Effect of regulations yet to be evaluated

Pros: • High corrosion resistance, only when double hull is left void

Pros: • Easy blasting, re-coating and renewing of side structure if necessary

Cons: • Extensive corrosion is envisioned if the hull space were used for ballast

Cons: • Hold frames are exposed to cargoes with high corrosion rates

Pros: • Improved resistance against low energy collision resulting in holds flooding

Pros: • Hold structure and hull girder are strengthened against one hold flooding, and easily maintained

Perception

Corrosion

Flooding resulting from damage to side structure

Mechanical Damage

Cons: • If side shell integrity were breached, one hold flooding may lead to a progressive flooding and loss of the ship Pros: • Hold side structure is protected from possible mechanical damage

Pros: • Hold frames are easily accessible for repairs

Cons: • Repair work of DSS structure may require hot work in confined space – both outer/inner hull

Cons: • Hold frames are vulnerable to mechanical damage during unloading

24 • Bulk Carrier Solutions: Safer and Stronger Vessels

Inspection and Maintenance

Steel Weight

DSS Bulk Carriers

SSS Bulk Carriers

Pros: • Access to DSS spaces will be facilitated using the hull structure – in the absence of ballast

Pros: • Hold structure and hull girder are strengthened against one hold flooding and easily maintained

Cons: • Maintenance work could be more challenging due to DSS spaces being confined

Cons: • Special means of access is necessary (permanent means of access is not feasible)

Pros: • Small difference as long as the strengthening for hold flooding is exempted in SOLAS XII

Pros: • Lighter than the same size for DSS BCs

Cons: • Heavier than the same size of SSS BCs – such effect may become larger of smaller BC

Bulk Carrier Solutions: Safer and Stronger Vessels • 25

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