1. Chapter 3 / The Propeller

2. Ch3. Propeller
Ahead movement
Astern movement
Transverse thrust

3. Ch3. Pitch of the propeller

4. Ch3. Right handed propeller

5. Ch3. Ahead / Direct Transverse thrust
Helical discharge from propeller creates a larger pressure on port side of rudder
Slight upward flow from the hull into propeller puts more pressure onto the down sweeping propeller blades
Speed of water into the propeller is eneven in velocity
Result: tendency to give a swing to port

6. Ch3. Ahead / Indirect transverse thrust

7. Ch3. Ahead / Indirect transverse thrust
Effect of propeller flow on the rudder: due to helical discharge
From propeller pressure of water more regular on left side of
Rudder
Result: increase the swing to port when running ahead

8. Ch.3. Ahead / Skin friction effect
Ship drags water along with it due to skin friction: reduction in flow
effects a big portion of propeller disc.
Variation of flow velocity changes the relative angle of incidence
to the rotating blades and creates an inbalance of drag forces in
upper and lower sections of propeller disc
Result: the ship turns to starboard

9. Ch3. Ahead / Transverse thrust
Direct effect: helical flow tends to turn the ship to port
Indirect effect: the upward flow on the propeller disc tends to turn the ship to port
The variation of velocity into the propeller disc tends to turn the ship to starboard
Resultant: the transverse thrust causes a gentle turn to Port

10. Ch3. Astern / Transverse thrust
Direct Effect
Water enters propeller disc at uniform
velocity and direction
Weak transverse force generated by difference of pressure on upper and lower propeller blades
Result
Gentle turn to starboard

11. Ch3. Astern / Transverse thrust
Indirect effect
Helical flow of propeller wash strikes after body of hull with
inward component on Ps and outward component on Sb:
Result is a higher pressure on Sb pushes stern to Ps.
Reverse flow over rudder and rudder effect reversed but weaker

12. Ch3. Astern / Transverse thrust
Conclusion:
pronounced turn to Sb when engine is going astern
Similar effect with headway, sternway of vessel stopped

13. Ch3. Astern / Transverse thrust
Crash Stop manœuvre:
In deep water, pronounced turn to Sb
In shallow water, trun less pronounced to the restriction of transverse components of propeller flow due to small UKC

14. Ch3. Interaction between propeller and rudder
Engine ahead:
Propeller flow strikes rudder
and increases the rudder
effect.
Action of propeller flow on
rudder more pronounced
when vessel is stopped or
with sternway.

15. Ch3. Interaction between propeller and rudder
Engine astern and Rudder amidships: the vessel is
Swinging to Starbard.

16. Ch3. Interaction between propeller and rudder
Engine astern and Rudder to Port: reverse effect on the
rudder and increased swing of vessel to starboard.
Effect more pronounced with vessel stopped or with
sterway

17. Ch3. Interaction between propeller and rudder
Engine astern and rudder to Sb: rudder effect opposes
transverse thrust
Vessel may swing to Port (rudder action bigger) or
keep a straight course or swing gently to Sb

18. Ch3. Interaction between propeller and rudder
Headway + engine astern + Sb. Rudder:
as long as the vessel keeps some headway: vessel turn to Sb
due to rudder + propeller effects
when vessel gets strenway, it may turn to port if rudder effect
greater than propeller effect.

19. Ch3. Interaction between propeller and rudder
Kick ahead manoeuver to regain control of a vessel with
sternway:
Rudder is put hard to port with engine ahead : turn to Sb due to effect
of propeller astern is stopped.

20. Ch3. Rudder counter effect to control propeller effect
Rudder to Sb
Engine astern
Put rudder amidships and gradually to Sb
End with rudder hard to Sb.

21. Ch.3. Kick ahead manoeuver
To increase significantly the rate of turn of a vessel
stopped or nearly stopped : short bursts of engine
ahead to increase the rudder effect.

22. Ch3. Negociating a bend with kick ahead
1. Vessel approaches with
reduced speed
2. Hard to port
3. Half or full ahead
4. Rate of turn increases
5. Short bursts on the engine
to avoid increase of speed
6. Reduce or stop the engine

23. Ch3. Half turn with right handed propeller
Pos 1: Rudder hard to Sb with engine
on half/full ahead
Pos 2: Rudder hard to port with engine
on half/full astern
Pos 3: Rudder hard to Sb with engine
Pos 3 : Half turn is completed.
Remark : The wind may modify or
even oppose this manœuvre.

24. Ch3. Half turn with right handed propeller
The previous manœuvre is only possible when the vessel starts
with the first turn to Sb. Otherwise will the propeller effect oppose
the rudder effect

25. Ch3. Half turn in heavy wind condition
Pos 1 : Engine half/full astern – the stern comes into the wind
Pos 2 : Rudder hard to port and engine half/full ahead
Pos 3 : Half turn completed

26. Ch3. Twin propellers
Handling characteristics depends of several factors:
Rudder configuration
Effect of torque
Transverse thrust
Pivot point
Turning ability

27. Ch3. Twin propellers / Rudder configuration
Single rudder is situated on the center line between the two propellers:
even with hard over is rudder partially or wholly out of propeller helical
discharge.
Very poor single rudder response at very slow speeds.

28. Ch3. Twin propellers / Torque effect
Torque effect: turning effect created by one engine astern
and one engine ahead or only one engine used.
poor effect with engines too close together (for exemple
on narrow beamed ships) – better to use the propellers
together with rudder as for a single screw ship.

29. Ch3. Twin propellers – Torque effect

30. Ch3. Parallel propeller shafts
Best configuration for handling capacity

31. Ch3. Convergent propeller shafts
Medium handling capacity

32. Ch3. Divergent propeller shafts
Poor handling capacity
no turning moment if shafts converge in the pivot point.

33. Ch3. Twin propellers / Outward turning
Outward turning fixed pitch
The blades are outward turning
In the upper half of the circle of
rotation when viewed from astern
If Sb propeller is put astern it will
be rotating in the opposite direction

34. Ch3. Twin propellers / Transverse thrust
Outward turning fixed pitch
propellers
(Sb ahead & Ps astern):
Helical discharge of Ps propeller
deflected up and onto Sb quarter
of the ship.
Transverse thrust is assisting the
torque effect and rudders to turn
the vessel to port.
Remark:Transverse thrust is a
poor force compared to rudder
force.

35. Ch3. Twin propellers / Transverse thrust
Inward turning fixed pitch propellers
If the ship is turning to port and the port propeller is put astern, it will be rotating in the opposite direction and is then acting as a left handed propeller on a single screw ship: part of the helical discharge will be deflected up and towards the starboard quarter.
The transverse thrust attempt to turn the bow to starboard in the opposite direction of the desired turn, working against the rudders and the torque effect.

36. Twin propellers / Transverse thrust
Inward turning (handed) fixed pitch propellers
The transverse thrust effect can be extremely severe
And render the vessel totally uncontrollable.
It is better to stop one engine and work the vessel as a single crew ship.
This configuration gives a better economical performance in terms of fuel consumption.

37. Ch3. Transverse thrust / Variable Pitch propellers
Inward turning:
The best configuration for CP
(controllable pitch) propellers:
the inside propeller during a turn
gives transverse thrust on the
appropriate quarter of the ship and
increase the effects of rudders and
torque.

38. Transverse thrust / Various configurations
1. Fixed outward turn 2. CP inward turn 3. CP outward turn

39. Pivot point position
Engine stopped /bowthruster to Sb:
Pivot point close (1/3L) to the stern
vessel turns on her heels: bow fast
to Sb.
Very effective with sternway

40. Pivot point position
Bowthruster stopped / Sb engine
astern / Ps engine ahead :
Pivot point close (1/3L) to bow
Bow turns slowly to Sb
Stern turns fast to port

41. Pivot point position
Bowthruster stopped / Sb engine
Ahead / Ps engine astern / rudders
Hard to Sb:
Pivot point very close (1/4L) to bow
Sterns goes to port
Rate of turn increased due to rudder
position

42. Ch3. Pivot point position
Bowthruster to Sb/ Sb engine astern/
Ps engine ahead / rudders amidships:
pivot point close to center of gravity
and behind
bow turns faster then stern due to
the position of the pivot point

43. Ch3. Position of pivot point
Bowthruster on / Ps engine ahead /
Sb engine astern / rudders hard Sb:
Pivot point at center of gravity
Ship turns around her center of gravity
Equal Rate of turns at bow and stern

44. Ch3. Voith Schneider propulsion

45. Ch3. Voith Schneider propulsion

46. Ch3. Voith Schneider propulsion
Multi directional propulsion unit /rotating vertical blades

47. Ch3. Voith Schneider propulsion
The use of two thrust units placed side by side
facilitating spectacular manoeuvrability of the
vessel

48. Ch3. Kort Nozzle

49. Ch3. Azipod propulsion
Rotating Azimuth
Unit.