Ship Handling Theory

SHIPHANDLING

OCS Class 2-04

TERMINAL PERFORMANCE

OBJECTIVEGiven a scenario as a break-in underway

Officer of the Deck (OOD), evaluate in writing the practical application of forces and procedures affecting the ship in various maneuvering scenarios in accordance with Crenshaw’s Naval Shiphandling and Knight’s Modern Seamanship.

ENABLING OBJECTIVES

• Identify and explain the effect of various forces, both controlled and uncontrolled, on an underway vessel.

• Identify a pivot point and explain factors affecting it.

• Identify and explain purpose of different lines aboard a moored vessel.

ENABLING OBJECTIVES(cont.)

• Explain procedures to get a moored vessel underway.

• Explain procedures to moor vessel to pier or wharf.

• Identify immediate reactions required from OOD in the event of a man overboard.

• Describe the various recovery methods for a man overboard.

SHIPHANDLING

• Mark of distinction for the professional mariner.

• As much of an art as it is a science.• Must understand the theory before you can

effectively grasp the lessons of practical exercises.

FORCES• Forces effect a ship’s movement.• Two types:

– Controllable– Uncontrollable

• Movement is the result of forces acting against a ship.

UNCONTROLLABLE FORCES

Those forces acting on a vessel which are out of the shiphandlers control:

• Wind• Current

– The force of one knot of current on a vessel is equivalent to approximately 30 Knots of wind.

• Visibility

UNCONTROLLABLE FORCES (cont.)

• Waves or Sea State

• Depth of water

• Confined waterways

CONTROLLABLE FORCES

• Propeller• Rudder • Lines• Anchor• Bow Thruster or Azimuth Thruster

INERTIA -- MOMENTUM

• Inertia: vessel’s tendency to remain at rest.

• Momentum: vessel’s tendency to remain in motion when in motion.

• Displacement: the volume or weight of water displaced by the hull (equaling the weight of the ship)

INERTIA -- MOMENTUM The greater the vessel’s displacement…

– the greater the inertia and momentum– the greater the friction of water against the

hull– the more power is needed to overcome

underwater and above water resistance– the longer it takes the vessel to accelerate or

decelerate– the lower the speed required to maintain

maneuverability.

BANK SUCTION

• What is Bank Suction?

• The bodily movement of a ship toward the near bank due to the decrease in pressure as a result of increased velocity of flow of water past the hull in a restricted channel.

BANK CUSHION

• What is Bank Cushion?

• In a restricted channel, especially one with steep banks, bank cushion tends to force the bow away from the bank due to increase in the bow wave on the near side.

SHALLOW WATER EFFECT

• As a ship moves through the water there is a change in the level of the bow and stern from the still water level.

• Moderate speeds: Vessel sinks and the stern squats

• Higher speeds: Sinkage stops, bow rises, stern continues to settle.

SHALLOW WATER EFFECT• What is Squat?

– For a vessel underway the bodily sinkage and change of trim caused by pressure changes on the hull due to the relative motion of water.

• Decreases speed• Lose rudder and propeller effect• Possibility of grounding

PROPULSION CONFIGURATIONS

• Single Screw• Twin Screw outboard• Twin Screw inboard• Controllable pitch propellers

PROPELLERS

• Right / Left handed• Propeller thrust: resultant force

transferred to ship from rotation of propeller.

• What does a propeller do?– Pressure differences– Thrust

PROPELLERS

• Side Force: moves or walks the stern of the vessel to one side or the other.

• Propeller moves and a force is created moving the stern in the direction of the rotating screw.

• Maximum effect when overcoming inertia

• Least effect when momentum is gained.

SCREW CURRENT

• The flow of water away from a turning propeller.

• Produces a large force against the rudder.

• Results in a large force against the rudder as well as the force created by the propeller to move the vessel fore or aft.

RUDDER EFFECT• The force generated by the pressure of

water against the flat surface of the rudder.

• Used to maintain or come to a desired heading.

• Rudder effect depends on:a. Amount of rudder appliedb. Vessel speedc. Rudder size

• The slower the ship's speed, the more rudder is needed to maintain course.

SINGLE SCREW MANEUVERING

• Casting: to turn a single screw ship in a restricted waterway

– Rudder put to right full and apply full power until headway is gained

– Shift rudder and apply back full until stern way is gained

– Continue the process

TWIN SCREW MANEUVERING

• Straight.• Turn on one shaft• Starboard ahead, bow goes _____________.• Port ahead, bow goes _______________.• Propellers versus rudders when

maneuvering• Screws opposed

PIVOT POINT

• The point on the center line which the ship pivots when the rudder is put over.

• The point of the ship upon which it turns and which scribes the “turning circle”

• When going ahead located about 1/3 the vessel's length aft of the bow.

MOVING THE PIVOT POINT

• Dredging anchor:– Pivot point moves to the hawse pipe.

• Vessel making sternway:– Pivot point moves above rudders.

• “Springing” alongside a pier:– Pivot point moves to chock of line to the pier.

TURNING CIRCLE• The path used by a vessel when

completing a 360 degree turn with constant rudder angle.

• Diameter will decrease with increased rudder angle or speed.

• Advance• Transfer• Tactical Diameter• Final Diameter

TURNING CIRCLE• The rudder is put over to start a turn -

the stern is forced away from the direction of the turn.

• The ship has to overcome the inertia resisting rotational acceleration - a few lengths of the ship passes before there is an effect

• Momentum causes the ship to continue in the original direction while coming to new course

Lines

STANDARD MOORING LINES

• Breast (or waist) lines: control lateral movement of moored vessel

• Spring lines: control fore and aft movement of moored vessel

GETTING UNDERWAY

• Take in breast lines• Take in quarter spring• Put rudder over to side of pier• Use bow spring line to assist in kicking

stern out• Rudder amidship• Take in bow spring

MOORING

• Assess conditions for mooring • Make approach between 10-15 degrees off

pier face (adjust as necessary for set)• Put over spring line• Take all way off • Pivot onto pier• Put over and secure all lines

MAN OVERBOARD

• What action is necessary? IMMEDIATE

• REHEARSE REHEARSE REHEARSE

MAN OVERBOARD INITIAL ACTION

• Right/Left full rudder, apply speed• Sound the alarm• Six short blasts• Break Oscar flag• Toss a life ring• Visual watch• Obtain a position• Muster

RECOVERY METHODS

• Shipboard pickup, person in the water.Windward or Leeward side?

• ANS: Leeward Side

• Small boat pickup.Under what circumstance is a small boat recovery preferred?

Shipboard Pickup

• Anderson Turn (Destroyer Turn)• Williamson Turn• Racetrack Turn• Y-Backing• Delayed Turn

Anderson Turn (Destroyer Turn)

Used by ships thathave considerablepower and relativelytight turning characteristics.

Williamson Turn

Used in low visibilitybecause it makes goodthe original track. Usedif it is believed that a personfell overboard some timeago and is not in sight.

Racetrack Turn

Y-Backing

Delayed Turn

Review Objectives

• What 2 kinds of forces affect a ship?• Define the following:

– Propeller thrust– Side force– Screw current– Rudder effect– Shallow Water Effect

Review Objectives (cont.)

• Where is the pivot point normally found?• What factors can change the pivot point

and to where?• What are the standard mooring lines and

their purposes?• Describe getting a vessel underway from

the pier.

Review Objectives (cont.)

• Describe mooring a vessel to a pier or wharf.

• What are the immediate reactions for a man overboard?

• On which side do we recover a man overboard?

Review Objectives (cont.)

• When would the following recovery methods be used:– Anderson Turn (Destroyer Turn)– Williamson Turn– Racetrack Turn– Y-Backing– Delayed Turn

QUESTIONS??