Chapter 3 / The Propeller

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Chapter 3 / The Propeller
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Ch3. Propeller

• Ahead movement
• Astern movement
• Transverse thrust

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Ch3. Pitch of the propeller
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Ch3. Right handed propeller
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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
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Ch3. Ahead / Indirect transverse thrust
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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
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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

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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

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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

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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

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Ch3. Astern / Transverse thrust

• Conclusion
• pronounced turn to Sb when engine is going astern
• Similar effect with headway, sternway of vessel
  stopped

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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

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

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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

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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.

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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.
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Ch3. Rudder counter effect to control propeller
effect

1. Rudder to Sb
2. Engine astern
3. Put rudder amidships and gradually to Sb
4. End with rudder hard to Sb.

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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.
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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
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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 on half/full
ahead Pos 3 Half turn is completed. Remark
The wind may modify or even oppose this
manœuvre.
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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
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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
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Ch3. Twin propellers

• Handling characteristics depends of several
  factors
• Rudder configuration
• Effect of torque
• Transverse thrust
• Pivot point
• Turning ability

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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.
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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.

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Ch3. Twin propellers Torque effect
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Ch3. Parallel propeller shafts
Best configuration for handling capacity
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Ch3. Convergent propeller shafts
Medium handling capacity
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Ch3. Divergent propeller shafts

• Poor handling capacity
• no turning moment if shafts converge in the
  pivot point.

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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
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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. RemarkTransverse thrust is a poor force
compared to rudder force.
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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.

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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.

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

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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

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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

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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

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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

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Ch3. Voith Schneider propulsion
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Ch3. Voith Schneider propulsion
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Ch3. Voith Schneider propulsion
Multi directional propulsion unit /rotating
vertical blades
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Ch3. Voith Schneider propulsion
The use of two thrust units placed side by side
facilitating spectacular manoeuvrability of the
vessel
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Ch3. Kort Nozzle
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Ch3. Azipod propulsion
Rotating Azimuth Unit.
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