chapter 2 / the rudder. ch2. forces acting on the ship / straight course with rudder amidships and...
TRANSCRIPT
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. 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. 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. Swinging room required when turning
-Stern of Ship A too close from berth to allow for a safe turn of A to starboard
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. 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. 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..)