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Ship Navigation Forces and Maneuvers Guide

Understand forces influencing ship navigation, rudder impact on turns, pivot point variations, rudder efficiency, and external factors affecting vessel maneuverability. Learn about rudder critical angles, turning characteristics related to wind, current, and ship form for safe navigation.

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Ship Navigation Forces and Maneuvers Guide

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  1. Chapter 2 / The Rudder

  2. 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

  3. Ch2. Forces acting on the ship / Rudder to Sb

  4. Ch2. Phase one of evolution to Sb The vessel starts turning to starboard but is slightly drifting to port

  5. 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

  6. 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 afterward of the center of gravity/ Pivot point: rate of turn and speed are constant.

  7. Ch2. Drift angle

  8. Ch2. Drift Angle

  9. Ch2. Drift angle at center of gravity

  10. Ch2. Pivot point / ship stopped Pivot point coincides with the center of gravity

  11. Ch2. Pivot Point / Speed ahead With headway: the pivot point is moving forward , as a result of the water pressure at the bow

  12. Ch2. Pivot Point / Speed Astern Pivot point is moving astern as a result of the water pressure on the stern

  13. 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

  14. Ch2. Avoiding an obstacle at short distance

  15. Ch2. Swinging room required when turning • Stern of Ship A too close from berth to allow for a safe • turn of A to starboard

  16. Ch2. Heeling Angles during a turn to port Fase 2 Fase one

  17. 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

  18. 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

  19. 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

  20. Ch2. Rudder critical angle / Stalling Phenomenon

  21. 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.

  22. 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

  23. Ch2. Comparison: slender and full bodied ships

  24. 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

  25. 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

  26. 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

  27. 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

  28. Ch2. Turning circle: • Rudder angle is • applied • 2. Ship enters her turn • 3. Variation of the heeling angles • 4. Turning diameter • 5. Transfer • 6. Advance • 7. Drift Angle

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