5Ch3. Ahead / Direct Transverse thrust Helical discharge from propeller creates a larger pressure on port side of rudderSlight upward flow from the hull into propeller puts more pressure onto the down sweeping propeller bladesSpeed of water into the propeller is eneven in velocityResult: tendency to give a swing to port
7Ch3. Ahead / Indirect transverse thrust Effect of propeller flow on the rudder: due to helical dischargeFrom propeller pressure of water more regular on left side ofRudderResult: increase the swing to port when running ahead
8Ch.3. Ahead / Skin friction effect Ship drags water along with it due to skin friction: reduction in floweffects a big portion of propeller disc.Variation of flow velocity changes the relative angle of incidenceto the rotating blades and creates an inbalance of drag forces inupper and lower sections of propeller discResult: the ship turns to starboard
9Ch3. Ahead / Transverse thrust Direct effect: helical flow tends to turn the ship to portIndirect effect: the upward flow on the propeller disc tends to turn the ship to portThe variation of velocity into the propeller disc tends to turn the ship to starboardResultant: the transverse thrust causes a gentle turn to Port
10Ch3. Astern / Transverse thrust Direct EffectWater enters propeller disc at uniformvelocity and directionWeak transverse force generated by difference of pressure on upper and lower propeller bladesResultGentle turn to starboard
11Ch3. Astern / Transverse thrust Indirect effectHelical flow of propeller wash strikes after body of hull withinward 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
12Ch3. Astern / Transverse thrust Conclusion:pronounced turn to Sb when engine is going asternSimilar effect with headway, sternway of vessel stopped
13Ch3. Astern / Transverse thrust Crash Stop manœuvre:In deep water, pronounced turn to SbIn shallow water, trun less pronounced to the restriction of transverse components of propeller flow due to small UKC
14Ch3. Interaction between propeller and rudder Engine ahead:Propeller flow strikes rudderand increases the ruddereffect.Action of propeller flow onrudder more pronouncedwhen vessel is stopped orwith sternway.
15Ch3. Interaction between propeller and rudder Engine astern and Rudder amidships: the vessel isSwinging to Starbard.
16Ch3. Interaction between propeller and rudder Engine astern and Rudder to Port: reverse effect on therudder and increased swing of vessel to starboard.Effect more pronounced with vessel stopped or withsterway
17Ch3. Interaction between propeller and rudder Engine astern and rudder to Sb: rudder effect opposestransverse thrustVessel may swing to Port (rudder action bigger) orkeep a straight course or swing gently to Sb
18Ch3. Interaction between propeller and rudder Headway + engine astern + Sb. Rudder:as long as the vessel keeps some headway: vessel turn to Sbdue to rudder + propeller effectswhen vessel gets strenway, it may turn to port if rudder effectgreater than propeller effect.
19Ch3. Interaction between propeller and rudder Kick ahead manoeuver to regain control of a vessel withsternway:Rudder is put hard to port with engine ahead : turn to Sb due to effectof propeller astern is stopped.
20Ch3. Rudder counter effect to control propeller effect Rudder to SbEngine asternPut rudder amidships and gradually to SbEnd with rudder hard to Sb.
21Ch.3. Kick ahead manoeuver To increase significantly the rate of turn of a vesselstopped or nearly stopped : short bursts of engineahead to increase the rudder effect.
22Ch3. Negociating a bend with kick ahead 1. Vessel approaches withreduced speed2. Hard to port3. Half or full ahead4. Rate of turn increases5. Short bursts on the engineto avoid increase of speed6. Reduce or stop the engine
23Ch3. Half turn with right handed propeller Pos 1: Rudder hard to Sb with engineon half/full aheadPos 2: Rudder hard to port with engineon half/full asternPos 3: Rudder hard to Sb with enginePos 3 : Half turn is completed.Remark : The wind may modify oreven oppose this manœuvre.
24Ch3. Half turn with right handed propeller The previous manœuvre is only possible when the vessel startswith the first turn to Sb. Otherwise will the propeller effect opposethe rudder effect
25Ch3. Half turn in heavy wind condition Pos 1 : Engine half/full astern – the stern comes into the windPos 2 : Rudder hard to port and engine half/full aheadPos 3 : Half turn completed
26Ch3. Twin propellersHandling characteristics depends of several factors:Rudder configurationEffect of torqueTransverse thrustPivot pointTurning ability
27Ch3. 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 helicaldischarge.Very poor single rudder response at very slow speeds.
28Ch3. Twin propellers / Torque effect Torque effect: turning effect created by one engine asternand one engine ahead or only one engine used.poor effect with engines too close together (for exempleon narrow beamed ships) – better to use the propellerstogether with rudder as for a single screw ship.
30Ch3. Parallel propeller shafts Best configuration for handling capacity
31Ch3. Convergent propeller shafts Medium handling capacity
32Ch3. Divergent propeller shafts Poor handling capacityno turning moment if shafts converge in the pivot point.
33Ch3. Twin propellers / Outward turning Outward turning fixed pitchThe blades are outward turningIn the upper half of the circle ofrotation when viewed from asternIf Sb propeller is put astern it willbe rotating in the opposite direction
34Ch3. Twin propellers / Transverse thrust Outward turning fixed pitchpropellers(Sb ahead & Ps astern):Helical discharge of Ps propellerdeflected up and onto Sb quarterof the ship.Transverse thrust is assisting thetorque effect and rudders to turnthe vessel to port.Remark:Transverse thrust is apoor force compared to rudderforce.
35Ch3. Twin propellers / Transverse thrust Inward turning fixed pitch propellersIf 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.
36Twin propellers / Transverse thrust Inward turning (handed) fixed pitch propellersThe transverse thrust effect can be extremely severeAnd 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.
37Ch3. Transverse thrust / Variable Pitch propellers Inward turning:The best configuration for CP(controllable pitch) propellers:the inside propeller during a turngives transverse thrust on theappropriate quarter of the ship andincrease the effects of rudders andtorque.
39Pivot point positionEngine stopped /bowthruster to Sb:Pivot point close (1/3L) to the sternvessel turns on her heels: bow fastto Sb.Very effective with sternway
40Pivot point positionBowthruster stopped / Sb engineastern / Ps engine ahead :Pivot point close (1/3L) to bowBow turns slowly to SbStern turns fast to port
41Pivot point positionBowthruster stopped / Sb engineAhead / Ps engine astern / ruddersHard to Sb:Pivot point very close (1/4L) to bowSterns goes to portRate of turn increased due to rudderposition
42Ch3. Pivot point position Bowthruster to Sb/ Sb engine astern/Ps engine ahead / rudders amidships:pivot point close to center of gravityand behindbow turns faster then stern due tothe position of the pivot point
43Ch3. Position of pivot point Bowthruster on / Ps engine ahead /Sb engine astern / rudders hard Sb:Pivot point at center of gravityShip turns around her center of gravityEqual Rate of turns at bow and stern