bowthruster. use of bowthruster / steering aid thrusters can be used : to assist steering at very...

BOWTHRUSTERBOWTHRUSTER

Use of Bowthruster / Steering aidUse of Bowthruster / Steering aid

Thrusters can be used : Thrusters can be used : • to assist steering at very slow speedto assist steering at very slow speed• to keep a ship’s position in the channel without to keep a ship’s position in the channel without

headway. (this capability is put to good use when headway. (this capability is put to good use when the ship is unable to proceed to the berth the ship is unable to proceed to the berth immediately because of an unexpected obstruction immediately because of an unexpected obstruction in the channel or a delay in tug availability, etc).in the channel or a delay in tug availability, etc).

• When navigating stern first,When navigating stern first, a bow thruster is more a bow thruster is more useful than a tug, provided the ship is not allowed to useful than a tug, provided the ship is not allowed to gather too much sternway.gather too much sternway.

Position of bowthruster: as far as possible forwardPosition of bowthruster: as far as possible forward

Use of bowthruster / Steering aidUse of bowthruster / Steering aid

• Altough slow to move a ship, thrusters provide a Altough slow to move a ship, thrusters provide a helpfull cushion when landing alongsidehelpfull cushion when landing alongside

• They are useful when a ship has to berth in a very They are useful when a ship has to berth in a very

tight corner with little manoeuvring space for a tugtight corner with little manoeuvring space for a tug

• Thrusters are useful when anchoringThrusters are useful when anchoring

• Thrusters may be accepted in lieu of a tug, Thrusters may be accepted in lieu of a tug, reducing the costs in port.reducing the costs in port.

2 thrusters to increase the power:2 thrusters to increase the power:

Reliability of bowthrustersReliability of bowthrusters

• Older units are proned to problems:Older units are proned to problems:– Outdated electrics and hydraulicsOutdated electrics and hydraulics– Situated in fore part of ship and subjected to heavy Situated in fore part of ship and subjected to heavy

weather,vibration and damp.weather,vibration and damp.– Negligence of maintenance Negligence of maintenance – lack of use on long sea passageslack of use on long sea passages

• New units:New units:– More reliable and robustMore reliable and robust

• Sometimes underpowered and inadequateSometimes underpowered and inadequate

Power of thrustersPower of thrusters

• More common: More common: – reversible electric motor driving a fixed pitch propellerreversible electric motor driving a fixed pitch propeller– Reversible electric motor + hydraulically operated variable Reversible electric motor + hydraulically operated variable

pitch propellerpitch propeller

• Limitation of Design parameters:Limitation of Design parameters:– Restricted locationRestricted location– Size of tunnelSize of tunnel– Ballast draftBallast draft– Hull strenghtHull strenght

• Limitation of power Limitation of power →→ Twin bowthrusters Twin bowthrusters• Many thrusters are equivalent to 10-15 tonnes Many thrusters are equivalent to 10-15 tonnes

bollard pullbollard pull

Counteracting forces near the tunnelCounteracting forces near the tunnel

These forces will vary with the vessel moving ahead, These forces will vary with the vessel moving ahead, astern or stopped. astern or stopped.

The effect of the thruster is the greatest when the ship The effect of the thruster is the greatest when the ship is stoppedis stopped

Counteracting forces near the tunnelCounteracting forces near the tunnel

In a ship moving aheadIn a ship moving ahead, , pressure fields will develop pressure fields will develop near the entrance and the near the entrance and the exit of the tunnel exit of the tunnel

The suction, acting over an The suction, acting over an area of plating, creates a area of plating, creates a force which is opposing force which is opposing the bow thruster. the bow thruster. This can This can reduce the effectiveness by reduce the effectiveness by 50% at a speed of 2 knots .50% at a speed of 2 knots .

Speed limitationSpeed limitation

• Most thrusters loose effectiveness as the ship Most thrusters loose effectiveness as the ship increases speed and are little or no help at speeds of increases speed and are little or no help at speeds of more than 3 or 4 knots more than 3 or 4 knots

• They may still exert some force until a speed of They may still exert some force until a speed of between 5 and 10 knots has been reached , between 5 and 10 knots has been reached , but the but the rudder would then be far more effective for turning rudder would then be far more effective for turning

the shipthe ship

Wind speed / ThrusterWind speed / ThrusterThruster A: 1000kwThruster A: 1000kwThruster B: 2000kwThruster B: 2000kw

1.1. Container ship 210m:Container ship 210m:

a)a) Thruster A enough forThruster A enough for a beam wind of max.a beam wind of max. 3 to 4 Beaufort3 to 4 Beaufort (11kn) (11kn)b) Thruster B enough forb) Thruster B enough for a beam wind of max.a beam wind of max. 4 to 5 Beaufort 4 to 5 Beaufort (16kn)(16kn)

2. Car carrier 200m:2. Car carrier 200m:

a) Thruster A enough fora) Thruster A enough for beam wind 4 Beaufortbeam wind 4 Beaufort (13kn)(13kn)b) B enough for beam b) B enough for beam wind up to 5 beaufortwind up to 5 beaufort (18kn)(18kn)

Thruster effectivenessThruster effectiveness

« Rudder action » versus « thruster action »« Rudder action » versus « thruster action »

DEAD SLOW AHEADDEAD SLOW AHEAD

1.1. Rudder to starboardRudder to starboard

Pivot Point moves forwardPivot Point moves forwardCenter of gravity moves to portCenter of gravity moves to port


DEAD SLOW AHEADDEAD SLOW AHEAD

2. Thruster action2. Thruster action

Pivot point moves asternPivot point moves asternCenter of gravity moves to SbCenter of gravity moves to SbThe ship « turns on her heels »The ship « turns on her heels »


FULL SPEED AHEADFULL SPEED AHEAD

1.1. Rudder actionRudder action

Pivot point moves forwardPivot point moves forwardCenter of gravity moves to PsCenter of gravity moves to Ps


FULL SPEED AHEADFULL SPEED AHEAD

2. Thruster action2. Thruster action

Pivot point forwardPivot point forward

Center of gravity moves to PsCenter of gravity moves to Psdue to difference in pressuredue to difference in pressurefields at the bow.fields at the bow.

No effectiveness of thruster withNo effectiveness of thruster withspeed aheadspeed ahead

Lateral motion to Port using rudder and bowthrusterLateral motion to Port using rudder and bowthruster

A.A. With short kicks aheadWith short kicks ahead and rudder hard to Sband rudder hard to Sb..

Moderate amount Moderate amount of thruster to port to of thruster to port to

compensate swing to compensate swing to SbSb

B. B. With astern powerWith astern power

• Transverse thrust of Transverse thrust of propellerpropeller

• Moderate thrust of Moderate thrust of bowthruster to port to bowthruster to port to compensate possible compensate possible swingswing

Lateral motion to Sb using rudder and bowthrusterLateral motion to Sb using rudder and bowthruster

A.A. Short kicks ahead + RudderShort kicks ahead + Rudder hard to port + thruster to Sbhard to port + thruster to Sb

No problems in lateral motionNo problems in lateral motion

B. B. With astern powerWith astern power

Bow swings to SbBow swings to Sb→ compensate→ compensate with Bowthruster to Portwith Bowthruster to Port

Thruster effect + transverse Thruster effect + transverse thrust cause unintentional thrust cause unintentional lateral motion to port.lateral motion to port.This movement can be of This movement can be of considerable magnitudeconsiderable magnitude

Specific aspects of bow thruster work:

• thrusting when stopped

• thrusting with headway

• creating lateral motion

• working the thruster with sternway

Thrusting when stoppedThrusting when stopped

Pivot point positionPivot point position

Thruster is working on pivot Thruster is working on pivot point located one ship’s point located one ship’s beam from stern (due to beam from stern (due to underwater profile of the underwater profile of the ship) ship) → large turning lever.→ large turning lever.

Turning momentTurning moment with ship with ship stopped is better than with:stopped is better than with: - headway- headway - sternway - sternway

Thrusting when stoppedThrusting when stopped

Ship develops small amount of headway due to a flow of water aroundShip develops small amount of headway due to a flow of water aroundthe bow creating a low pressure ahead of the shipthe bow creating a low pressure ahead of the ship

Thrusting with headway / Straight lineThrusting with headway / Straight line

• performance falls off rapidly wit speedperformance falls off rapidly wit speed> 2knots> 2knots • pivot point position reduces the turning leverpivot point position reduces the turning lever → → poor turning momentpoor turning moment

Thrusting with headway / Perfomance lossThrusting with headway / Perfomance loss

Thrusting with headway / TurningThrusting with headway / Turning

1. When the rudder is applied with a kick ahead and no speed, pivot1. When the rudder is applied with a kick ahead and no speed, pivot point moves briefly forward to P, close to the thruster position point moves briefly forward to P, close to the thruster position → no → no turning lever / bow is only pushed sidewaysturning lever / bow is only pushed sideways

2. When vessels gets some speed: pivot point moves to P1 but 2. When vessels gets some speed: pivot point moves to P1 but adverseadverse effect of speed effect of speed

Thrusting with headway / TurningThrusting with headway / Turning

3. Thruster may be very useful to develop lateral motion in conjunction3. Thruster may be very useful to develop lateral motion in conjunction with propeller and rudder. with propeller and rudder. for example: rudder to port and thruster to starboard for example: rudder to port and thruster to starboard → bow and stern→ bow and stern tends to move to Sb and ships moves sidewaystends to move to Sb and ships moves sideways

Lateral motion to port with kicks aheadLateral motion to port with kicks ahead

Frequently used when berthing: driving a ship « by the seat of theFrequently used when berthing: driving a ship « by the seat of thepants »pants »On large vessels moving sideways, the kinetic energy can carry onOn large vessels moving sideways, the kinetic energy can carry on for quite some timefor quite some timeSometimes difficult to balance the forces of rudder and thruster: Sometimes difficult to balance the forces of rudder and thruster: Full thruster of 13t is only equal to kick ahead with dead slowFull thruster of 13t is only equal to kick ahead with dead slow

Lateral motion to port with astern powerLateral motion to port with astern power

• When putting propeller astern ,anticipated swing of bow to Sb can When putting propeller astern ,anticipated swing of bow to Sb can be stopped by applying port thruster.be stopped by applying port thruster.• Very effective with large tonnage ships / some caution required toVery effective with large tonnage ships / some caution required to avoid landing too fast and too heavilyavoid landing too fast and too heavily

Lateral motion to starboard with kicks aheadLateral motion to starboard with kicks ahead

Same way as for a lateral motion to port.Same way as for a lateral motion to port.Problem arise when the engine is reversed (see next slide)Problem arise when the engine is reversed (see next slide)

Lateral motion to starboard with astern powerLateral motion to starboard with astern power

swing

More problematic to starboard More problematic to starboard (with single screw)(with single screw)

When astern power is appliedWhen astern power is applied (to control headway):(to control headway):• bow swings to Sbbow swings to Sb• tendency to give thruster totendency to give thruster to Ps will bring ships back to initialPs will bring ships back to initial position.position.

Thrusting with sternwayThrusting with sternway

• pivot point moves aft : big turning lever for the thruster / possible topivot point moves aft : big turning lever for the thruster / possible to steer the vessel with the bowthrustersteer the vessel with the bowthruster• beware forbeware for poor thruster power and sluggish response of vesselpoor thruster power and sluggish response of vessel• avoid the development of a big rate of turn: difficult to controlavoid the development of a big rate of turn: difficult to control

Thrusting with sternway / Turning moments of Thrusting with sternway / Turning moments of propeller and bowthrusterpropeller and bowthruster

If the engine is going astern (200m ship/ transverse forces If the engine is going astern (200m ship/ transverse forces respectively 7t - propeller and 13t- thruster) : respectively 7t - propeller and 13t- thruster) : • transverse thrust of propeller pushes the bow to Sbtransverse thrust of propeller pushes the bow to Sb turning lever of propeller = 30m turning lever of propeller = 30m → thrust = 7t x 30m = 210 tm→ thrust = 7t x 30m = 210 tm• bowthruster turning lever = 125m → 13t x 125m = 1625mt (contd)bowthruster turning lever = 125m → 13t x 125m = 1625mt (contd)

Thrusting with sternway / Turning moments of Thrusting with sternway / Turning moments of propeller and bowthrusterpropeller and bowthruster

Therefore it is possible to work the vessel astern by overridingTherefore it is possible to work the vessel astern by overridingThe effect of transverse thrust with the bow thruster.The effect of transverse thrust with the bow thruster.→ → It may often be preferred to back up a waterway or to a berthIt may often be preferred to back up a waterway or to a berth

Bowthruster at workBowthruster at work

Working astern in a channelWorking astern in a channelLack of experience ends up with the ship Lack of experience ends up with the ship in a difficult position (pos6)in a difficult position (pos6)

Working astern in a channelWorking astern in a channel

The process ofThe process of backing a ship up a waterway with the backing a ship up a waterway with the aid of a bowthruster can be dangerous:aid of a bowthruster can be dangerous:

The inexperienced can unintentionally allow the ship to The inexperienced can unintentionally allow the ship to become a victim of unexpected influence of become a victim of unexpected influence of transverse thrust and insidious drifttransverse thrust and insidious drift

→→ For this manœuvre, large ships use often the For this manœuvre, large ships use often the assistance of a tug secured aft to assist steering and assistance of a tug secured aft to assist steering and positioning of the stern / the bowthruster controls positioning of the stern / the bowthruster controls the bow.the bow.

Position 1Position 1

•Ship has entered the channelShip has entered the channel

•Good position with bow canted to Good position with bow canted to port to allow for prolonged use of port to allow for prolonged use of stern power and transverse thruststern power and transverse thrust


• Insufficient correction of transverse Insufficient correction of transverse thrust thrust → stern has dropped away from → stern has dropped away from centre of channelcentre of channel

• If propeller and thruster are now used If propeller and thruster are now used simultaneously: lateral motion to portsimultaneously: lateral motion to port

• this is not intentional and may be this is not intentional and may be unnoticedunnoticed


• ship steady on correct heading but offship steady on correct heading but off centeredcentered

• at this stage: at this stage: use bow thrusteruse bow thruster vigorously / vigorously / or:or: kick ahead with rudder to kick ahead with rudder to port port to bring stern back to the centre of to bring stern back to the centre of the channelthe channel


Sequence of events in position 2 is Sequence of events in position 2 is repeated repeated →→ ship keeps drifting to port ship keeps drifting to port

On very large vessels, the kinetic On very large vessels, the kinetic energy keep the vessel drifting for a energy keep the vessel drifting for a long time.long time.

A light wind on the Sb side will A light wind on the Sb side will increase the drift.increase the drift.


The ship is getting too close to the The ship is getting too close to the edge and is running out of edge and is running out of manoeuvring spacemanoeuvring space

There is insufficient water to port to There is insufficient water to port to enable the bow to be thrusted to enable the bow to be thrusted to portport


The ship ultimately is hitting an The ship ultimately is hitting an obstruction on the port side.obstruction on the port side.

To avoid this kind of manœuvre:To avoid this kind of manœuvre:

1.1. Get the ship moving smartly astern initially and keep it movingGet the ship moving smartly astern initially and keep it moving

2.2. Use kick aheads with caution: it takes the way off the ship which Use kick aheads with caution: it takes the way off the ship which can drift out of position with leewaycan drift out of position with leeway

3.3. No attempt in transverse winds overriding the thruster’s powerNo attempt in transverse winds overriding the thruster’s power

4.4. When sufficient sternway: stop the engine to avoid transverse When sufficient sternway: stop the engine to avoid transverse thrustthrust

5.5. Watch the heading carefully at all times and use thruster Watch the heading carefully at all times and use thruster vigorouslyvigorously to keep to keep the sternthe stern on the intended track / the rest will on the intended track / the rest will follow.follow.

Working astern to a berthWorking astern to a berth

The position of the pivot point: ships goesThe position of the pivot point: ships goes slowly astern and turns to Sb.slowly astern and turns to Sb.


With engine ahead it is easy to correct a too high approach With engine ahead it is easy to correct a too high approach speedspeedor an unaccurate positioning of the sternor an unaccurate positioning of the stern


With engine stopped and bowthruster in useWith engine stopped and bowthruster in use: pivot point moves: pivot point moves after and bowthruster works on a large turning leverafter and bowthruster works on a large turning lever

Leaving a berthLeaving a berth

1.1. Vessel turns around a pivot point situated forward: stern leaves theVessel turns around a pivot point situated forward: stern leaves the berthberth2.2. « Let go all lines fwd » and thruster to Sb: with engine stopped and « Let go all lines fwd » and thruster to Sb: with engine stopped and thruster at work the pivot point moves to pos. « b » and the bowthruster at work the pivot point moves to pos. « b » and the bow leaves the berthleaves the berth

Leaving a berthLeaving a berth

Small ships often use a combination of forward spring + Small ships often use a combination of forward spring + rudder + propeller + bowthrusterrudder + propeller + bowthruster

Backing in a narrow canal with beam windBacking in a narrow canal with beam wind

« Transverse thrust + bowthruster effect + wind effect » push« Transverse thrust + bowthruster effect + wind effect » pushvessel to port: vessel to port: 2 tons of the propeller and 5 tons of the bow thruster2 tons of the propeller and 5 tons of the bow thruster (pivot point between midships and stern).(pivot point between midships and stern). This means a total transverse force on the ship of 7 tons to portThis means a total transverse force on the ship of 7 tons to port

Comparison: Turning a vessel with little headway:Comparison: Turning a vessel with little headway:

1.1. With bowthruster onlyWith bowthruster only

2.2. With a combination of bowthruster, rudder & propellerWith a combination of bowthruster, rudder & propeller

Ship with headway / Using only the bowthrusterShip with headway / Using only the bowthruster

• As soon as the ship starts turning,As soon as the ship starts turning, the pivot point will be the pivot point will be situated somewhere between the stern and midships. situated somewhere between the stern and midships.

• Although the lever of the turning moment is large, the effect will Although the lever of the turning moment is large, the effect will be very low, because :be very low, because :1. the effectiveness of the bow thruster is very small 1. the effectiveness of the bow thruster is very small 2. the effectiveness is decreasing rapidly with the ship’s speed 2. the effectiveness is decreasing rapidly with the ship’s speed

ahead ahead 3. there is high water pressure at the bow and consequently 3. there is high water pressure at the bow and consequently

the lateral resistance of the ship is highest near the fore ship the lateral resistance of the ship is highest near the fore ship and is increasing with the speed. The bow thruster has to and is increasing with the speed. The bow thruster has to push the bow against the bow wave.push the bow against the bow wave.

The consequence is, that at a forward speed of about 4 knots, the The consequence is, that at a forward speed of about 4 knots, the bow thruster is too weak to overcome the lateral resistance and bow thruster is too weak to overcome the lateral resistance and to push the bow to starboardto push the bow to starboard.

Ship with headway / Combining thruster , rudder & Ship with headway / Combining thruster , rudder & propellerpropeller

• 1. we first start by using only the rudder and the propellor: the 1. we first start by using only the rudder and the propellor: the pivot point moves ahead, between the bow and midships, the pivot point moves ahead, between the bow and midships, the exact location depending of the ratio of the ship’s lenght to exact location depending of the ratio of the ship’s lenght to beam (L/B). The high lateral resistance at the bow, the bow beam (L/B). The high lateral resistance at the bow, the bow wave, will now have a favourable influence on the turn.wave, will now have a favourable influence on the turn.

• 2. Then, the bow thruster is started to starboard: it will 2. Then, the bow thruster is started to starboard: it will increase the rate of turn, in spite of a short lever (pivot point increase the rate of turn, in spite of a short lever (pivot point ahead). ahead).

Twin screw ship + bowthrusterTwin screw ship + bowthruster

Crablike movementCrablike movement

New DesignsNew Designs

Anti-suction tunnelAnti-suction tunnel

Additional tunnel improves performanceAdditional tunnel improves performance

Anti-suction tunnelAnti-suction tunnel

• To solve this problem of the counteracting force, an To solve this problem of the counteracting force, an extra tunnel is sometimes constructed behind the extra tunnel is sometimes constructed behind the bow thruster tunnel to connect the negative and bow thruster tunnel to connect the negative and positive pressure fields : this is the AST tunnel positive pressure fields : this is the AST tunnel ( anti suction) . ( anti suction) .

K-JetK-Jet

Altering the shape of tunnel Altering the shape of tunnel apertures to improve the waterflowapertures to improve the waterflowthrough the tunnel and avoid through the tunnel and avoid turbulencesturbulences

NavyfluxNavyflux

Veth-Jet bowthruster Veth-Jet bowthruster

With the help of a With the help of a horizontal propeller, water horizontal propeller, water is sucked up from is sucked up from underneath the vessel. underneath the vessel.

The vessel is manoeuvred The vessel is manoeuvred by means of a 360 degrees by means of a 360 degrees rotating deflector, which rotating deflector, which turns the water through 90 turns the water through 90 deg. and forces it through deg. and forces it through aa tunnel.tunnel.

Veth-Jet bowthruster Veth-Jet bowthruster

maximum thrust can be achieved even at minimum draught, without maximum thrust can be achieved even at minimum draught, without any component parts protruding from under the ship. Thrust can be any component parts protruding from under the ship. Thrust can be maintained for longer than a tunnel thruster, even during speed-up, maintained for longer than a tunnel thruster, even during speed-up, by virtue of the fact that the water is sucked up from underneath the by virtue of the fact that the water is sucked up from underneath the vessel.vessel.

Other application: Vessel blocked by iceOther application: Vessel blocked by ice

Other application: Purse seiner with bowthrusterOther application: Purse seiner with bowthruster

Ship equipped with a stern thrusterShip equipped with a stern thruster

bowthruster. use of bowthruster / steering aid thrusters can be used : to assist steering at very...

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