Chapter 2 / The RudderChapter 2 / The Rudder

Ch2. Forces acting on the ship / Straight course

With Rudder amidships and constant speed:

Thrust due to the propellor and resistance of the water in the longitudinal direction are in equilibrium

Ch2. Forces acting on the ship / Rudder to Sb

Ch2. Phase one of evolution to Sb

The vessel starts turning to starboard but is slightly drifting to port

Ch2. Phase 2 of evolution to Sb

- Water resistance is shifting to port accelerating the turning moment to starboard-Force Q1 opposes force Q-Speed is diminishing

Ch2. Phase 3 of evolution to Sb

Equilibrium between the force on the rudder and the forces exerted by the water on the portside hull forward and afterwardof the center of gravity/ Pivot point: rate of turn and speed are constant.

Ch2. Drift angle

Ch2. Drift Angle

Ch2. Drift angle at center of gravity

Ch2. Pivot point / ship stopped

Pivot point coincides with the center of gravity

Ch2. Pivot Point / Speed ahead

With headway: the pivot point is moving forward , as a result of the water pressure at the bow

Ch2. Pivot Point / Speed Astern

Pivot point is moving astern as a result of the water pressure on the stern

Ch2. Influence of Block coefficent on Pivot Point

The pivot point of a vessel with a large block coefficient is closer to the bow: the efficiency of the rudder (steering capacity) increases

Ch2. Avoiding an obstacle at short distance

Ch2. Swinging room required when turning

-Stern of Ship A too close from berth to allow for a safe turn of A to starboard

Ch2. Heeling Angles during a turn to port

Fase one Fase 2

Ch2. Change of trim during a turn

Point of application of ware resistance on the rudder is lower that the centre of gravity/ pivot point: a change of trim by the head is occuring during a turn

Ch2. Reduced rudder effect with sternway

- Water resistance applies on back of rudder: effect reversed- Propellor wash does not strike the rudder- Pivot point moves astern and turning lever of rudder force is reduced

Ch2. Maximum rudder efficiency

- Maximum rudder efficiency is obtained with a rudder angle of approx. 30° to 35°-The best compromise between rudder efficiency (lift)and water resistance (drag) is obtained with this value of the rudder angle

Ch2. Rudder critical angle / Stalling Phenomenon

Ch2. Influence of list on a turn

The vessel is listing to Port and has a normal tendency to turn to port: will favour port rudder but reduce starboard rudder.

Ch2. Influence of Block coefficient on turning characteristics

Containership : Cb = 0,6 Tanker: Cb = 0,8

• Transfer and tactical diameter practically similar

• Turning radius of tanker much smaller

• Drift angle of tanker much bigger

• Pivot point of tanker closer to the bow

Ch2. Comparison: slender and full bodied ships

Ch2. Form of the ends

• Ship A is equipped with a bulb and has a better directional stability and offers a bigger lateral resistance during a turn than ship B• Ship B enters earlier in his turn than A

Ch2. Effect of wind on a turn

•Between a and b’: turns faster •Between b’ and c’: turns slower•Between c’ and d’: turns faster•Between d’ and e’:turns slower

Ch2. Effect of the current on a turn

•The vessel is moving together with the mass of water • The vessel drift in the direction of the current

Ch2. Rate of turn Indicator

This instrument is very important:

• It indicates the speed of the turn(number of degrees in one minute)

• it marks « zero » when the vessel is stabilised on a straight course

Ch2. Turning circle:

1. Rudder angle is applied2. Ship enters her

turn3. Variation of the

heeling angles4. Turning diameter5. Transfer6. Advance7. Drift Angle

Ordres de barre standardsZéro la barreBabord (ou tribord) cinq , dix , quinze , vingt .Babord (ou tribord) toute .Droit comme ça .Quel est votre cap?Gouvernez ..... 124 ( un deux quatre) 217 ( deux un sept ) 000 ( zéro zéro zéro) Rien à babord / tribordDoucement la barreRevenez doucementBabord / tribord un peuRencontrezSurveillez la gouverneDroit sur ... (phare)

Standaard roerbevelenRoer midscheepsBakboord vijf , tien , vijftien, twintig .Hard bakboord ( stuurboord)Recht zo Wat is uw voorligging?Stuur ..... 124 ( een twee vier ) 217 ( twee een seven ) 000 ( nul nul nul )Niets aan bakboord /stuurboordMinder roer geven Langzaam opkomen Een weinig bak / stuurboordTegenroer gevenOpgelet aan het roerRechtaan op ... (vuurtoren ..)

Standard helm ordersMidships the rudderPort five , ten , fifteen , twenty .Hard to port (starboard)Steady as you go What’s your heading?Steer ..... 124 ( one two four) 217 ( two one seven ) 000 ( zero zero zero )Nothing to port / starboard Easy ( ease the rudder )Come back easyPort / starboard easyMeet herMind / watch the rudderSteady on ... ( lighthouse..)