Chapter 2 / The Rudder

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Chapter 2 / The Rudder
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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
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Ch2. Forces acting on the ship / Rudder to Sb
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Ch2. Phase one of evolution to Sb
The vessel starts turning to starboard but is
slightly drifting to port
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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

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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.
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Ch2. Drift angle
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Ch2. Drift Angle
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Ch2. Drift angle at center of gravity
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Ch2. Pivot point / ship stopped
Pivot point coincides with the center of gravity
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Ch2. Pivot Point / Speed ahead
With headway the pivot point is moving forward ,
as a result of the water pressure at the bow
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Ch2. Pivot Point / Speed Astern
Pivot point is moving astern as a result of the
water pressure on the stern
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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
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Ch2. Avoiding an obstacle at short distance
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Ch2. Swinging room required when turning

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

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

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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

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Ch2. Rudder critical angle / Stalling Phenomenon
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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.
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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

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Ch2. Comparison slender and full bodied ships
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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

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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 eturns slower

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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

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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

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• 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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Ordres de barre standards Zéro la barre Babord (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 / tribord Doucement la barre Revenez doucement Babord / tribord un peu Rencontrez Surveillez la gouverne Droit sur ... (phare) Standaard roerbevelen Roer midscheeps Bakboord 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 /stuurboord Minder roer geven Langzaam opkomen Een weinig bak / stuurboord Tegenroer geven Opgelet aan het roer Rechtaan op ... (vuurtoren ..) Standard helm orders Midships the rudder Port five , ten , fifteen , twenty . Hard to port (starboard) Steady as you go Whats 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 easy Port / starboard easy Meet her Mind / watch the rudder Steady on ... ( lighthouse..)
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