Chapter 2 / The Rudder
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. Forces acting on the ship / Rudder to Sb
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 afterward
of the center of gravity/ Pivot point: rate of turn and speed
are constant.
Ch2. Drift angle
Ch2. Drift Angle
Ch2. Drift angle at center of gravity
Ch2. Pivot point / ship stopped
Pivot point coincides with the center of gravity
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. Avoiding an obstacle at short distance
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. Heeling Angles during a turn to port
Fase one
Fase 2
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. Rudder critical angle / Stalling Phenomenon
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. Comparison: slender and full bodied ships
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
applied
2. Ship enters her
turn
3. Variation of the
heeling angles
4. Turning diameter
5. Transfer
6. Advance
7. Drift Angle
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
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 easy
Port / starboard easy
Meet her
Mind / watch the rudder
Steady on ... (
lighthouse..)