Ship Handling

 

Ship manoeuvring fundamentals

 

Ship handling theory Newton’s First Law of Motion Newton’s An object in motion tends to stay in motion. An object at rest tends to stay at rest. (Unless acted upon by an outside force)

Newton’s Newton’s Second Law of Motion The resulting motion of an object is the sum of all forces acting on it. Newton’s Newton’ s Third Law of Motion Every action has an equal and opposite reaction.

 

Three basic categories of forces

Uncontrollable Controllable Semi-controllable

 

Controllable Forces Propellers Rudder  Bow Thrusters Mooring Lines Anchors Tugs

 

Uncontrollable Forces Weather conditions Sea conditions Water depth Width of fairway Traffic density

 

Propellers Provides the most important source of force on a ship. (Usually) makes ship go forward.

Most ships have 2 propellers.

 

Propellers Forces resulting from propellers: •

the use of the

Forward (or reverse) thrust

•

Side Force

•

Side Force

Bottom

 

Fixed Pitch Propellers Cannot change pitch of propeller 

•

Thrust (speed) controlled by changing speed of thE shaft

•

To go backwards, must stop shaft and spin the shaft in the opposite direction.

•

 

Rudders Used to control ship’s heading by moving the stern. To have an effect, must have a flow of water across the rudder ru dder.. Normally this flow of water is the discharge current of the screw.

 

Rudders  Acts a wing Rudder amidships

Water  Flow

 

Rudders

Acts a wing

Water  Flow

Rudder PS High Pressure Area

Low Pressure Area Rudder  Force

 

Rudders

Acts a wing

Water  Flow

Rudder SB Low Pressure Area Rudder  Force

High Pressure Area

 

Propellers / Rudders Primary means of controlling the stern

Thrust

Side Force right turning propeller  Rudder Force

 

Pivot Point Imaginary point on the ship’ ship’s s centerline which the ship pivots •

about

Pivot Point Thrust Side Force Rudder Force

 

Pivot Point Usually located 1/3 the length of the ship from the bow bow.. •

Pivot point is not fixed

•

 

Pivot Point Forces which affect location of the Pivot Point Headway or Sternway Ship’s Speed Anchors Mooring Lines Tugs

 

Wind Acts on the sail area of the ship Exposed superstructure Hull structure Ships tend to back into the wind (?) 30kts of wind = 1kts of current

 

Currents Acts on the underwater part of the ship. Navigator continuously computes set and drift.

 

Semi-controllable Forces Shallow water effects Squat Bank suction Increased tactical diameter 

Passing ships effect Meeting Overtaking

 

SHALLOW WATER EFFECTS Depth of Water Squat - Occ Squat Occurs urs a high high speed speeds s bow of a ship rides up onto the bow wave stern of a ship tends to sink Normally not a problem. In shallow water, water, depth of water may not be deep enough causing the propellers to hit the bottom.

 

SHALLOW WATER EFFECTS Squat Proportional to

•

Speed Displacement Depth and breadth of the water  Can cause ship to strike the bottom

•

•

Reduce rudder effectiveness Less speed

•

Ship’s wake can be an indicator 

•

 

SHALLOW WATER EFFECTS SQUAT

2.5 X DRAFT

SLOW DOWN TO REDUCE EFFECTS

 

SHALLOW WATER EFFECTS Bank suction/Cushion

 

PASSING SHIP EFFECTS MEETING/OVERTAKING

 

Ship handling handling Terms Turning Circle The path described by a ship’s pivott point pivo point as it execute executes s a 360° 360° turn.

 

Turning Circle

Tactical Diameter (180°) Final Diameter (360°)

 

Turning Circle

Kick Final Diameter  Tactical Diameter 

 

Ship handling handling Terms  Advance Distance gained toward the direction of the original course after the rudder is put over over..

Transfer  Distance gained perpendicular to the original course after the rudder is put over.

 

Advanc e & Tran Transfer sfer 90° 90° Turn Advance

Transfer 

Kick

    e     c     n     a     v       d       A

 

Advance Transfe sferr 180° Turn Advance & Tran

Transfer      e     c     n     a     v       d       A

Kick

 

Advance & Tran Advance Transfe sferr 360° Turn Transfer 

Kick

A   d  v  a n  c   e

 

Ship handling handling Terms Headway moving forward through the water Sternway moving backwards through the water Bare Steerageway the minimum speed a ship can proceed and still maintain course using the rudders

 

Single Screw Ships

 

Ship Ahead Propeller Ahead (right turning) Rudder Amidships

Water resistance+ Water resistance++

 

Water resistance+

Ship Astern Propeller Astern Rudder Amidships Water resistance++

Ship follows the rudder: Ship will tend into the wind: Ship will tend to port very easily Ship does not tend to starboard easily

 

Ship Ahead

It depends the resultant of the

Propeller Astern water flow to the rudder Rudder Amidships

Water current flow ship >> the discharge ofahead the screw Ship will attend to go to SB Water flow ship ahead