1. BOWTHRUSTER

2. Use of Bowthruster / Steering aid
Thrusters can be used :
to assist steering at very slow speed
to keep a ship’s position in the channel without headway. (this capability is put to good use when the ship is unable to proceed to the berth immediately because of an unexpected obstruction in the channel or a delay in tug availability, etc).
When navigating stern first, a bow thruster is more useful than a tug, provided the ship is not allowed to gather too much sternway.

3. Position of bowthruster: as far as possible forward

4. Use of bowthruster / Steering aid
Altough slow to move a ship, thrusters provide a helpfull cushion when landing alongside
They are useful when a ship has to berth in a very tight corner with little manoeuvring space for a tug
Thrusters are useful when anchoring
Thrusters may be accepted in lieu of a tug, reducing the costs in port.

5. 2 thrusters to increase the power:

6. Reliability of bowthrusters
Older units are proned to problems:
Outdated electrics and hydraulics
Situated in fore part of ship and subjected to heavy weather,vibration and damp.
Negligence of maintenance
lack of use on long sea passages
New units:
More reliable and robust
Sometimes underpowered and inadequate

8. Limitation of Design parameters:
Power of thrusters
More common:
reversible electric motor driving a fixed pitch propeller
Reversible electric motor + hydraulically operated variable pitch propeller
Limitation of Design parameters:
Restricted location
Size of tunnel
Ballast draft
Hull strenght
Limitation of power → Twin bowthrusters
Many thrusters are equivalent to tonnes bollard pull

9. Counteracting forces near the tunnel
These forces will vary with the vessel moving ahead, astern or stopped.
The effect of the thruster is the greatest when the ship is stopped

10. Counteracting forces near the tunnel
In a ship moving ahead, pressure fields will develop near the entrance and the exit of the tunnel
The suction, acting over an area of plating, creates a force which is opposing the bow thruster. This can reduce the effectiveness by 50% at a speed of 2 knots .

12. Speed limitation
Most thrusters loose effectiveness as the ship increases speed and are little or no help at speeds of more than 3 or 4 knots
They may still exert some force until a speed of between 5 and 10 knots has been reached , but the rudder would then be far more effective for turning the ship

13. Wind speed / Thruster Thruster A: 1000kw Thruster B: 2000kw
Container ship 210m:
Thruster A enough for
a beam wind of max.
3 to 4 Beaufort (11kn)
b) Thruster B enough for
4 to 5 Beaufort (16kn)
2. Car carrier 200m:
a) Thruster A enough for
beam wind 4 Beaufort
(13kn)
b) B enough for beam
wind up to 5 beaufort
(18kn)

15. Thruster effectiveness

16. « Rudder action » versus « thruster action »
DEAD SLOW AHEAD
Rudder to starboard
Pivot Point moves forward
Center of gravity moves to port

17. « Rudder action » versus « thruster action »
DEAD SLOW AHEAD
2. Thruster action
Pivot point moves astern
Center of gravity moves to Sb
The ship « turns on her heels »

18. « Rudder action » versus « thruster action »
FULL SPEED AHEAD
Rudder action
Pivot point moves forward
Center of gravity moves to Ps

19. « Rudder action » versus « thruster action »
FULL SPEED AHEAD
2. Thruster action
Pivot point forward
Center of gravity moves to Ps
due to difference in pressure
fields at the bow.
No effectiveness of thruster with
speed ahead

21. Lateral motion to Port using rudder and bowthruster
With short kicks ahead
and rudder hard to Sb.
Moderate amount
of thruster to port to compensate swing to Sb
B. With astern power
Transverse thrust of propeller
Moderate thrust of bowthruster to port to compensate possible swing

22. Lateral motion to Sb using rudder and bowthruster
Short kicks ahead + Rudder
hard to port + thruster to Sb
No problems in lateral motion
B. With astern power
Bow swings to Sb→ compensate
with Bowthruster to Port
Thruster effect + transverse
thrust cause unintentional
lateral motion to port.
This movement can be of
considerable magnitude

23. Specific aspects of bow thruster work:
thrusting when stopped
thrusting with headway
creating lateral motion
working the thruster with sternway

24. Thrusting when stopped
Pivot point position
Thruster is working on pivot point located one ship’s beam from stern (due to underwater profile of the ship) → large turning lever.
Turning moment with ship stopped is better than with:
- headway
- sternway

25. Thrusting when stopped
Ship develops small amount of headway due to a flow of water around
the bow creating a low pressure ahead of the ship

26. Thrusting with headway / Straight line
performance falls off rapidly wit speed> 2knots
pivot point position reduces the turning lever
→ poor turning moment

27. Thrusting with headway / Perfomance loss

28. Thrusting with headway / Turning
1. When the rudder is applied with a kick ahead and no speed, pivot
point moves briefly forward to P, close to the thruster position → no
turning lever / bow is only pushed sideways
2. When vessels gets some speed: pivot point moves to P1 but adverse
effect of speed

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

30. Lateral motion to port with kicks ahead
Frequently used when berthing: driving a ship « by the seat of the
pants »
On large vessels moving sideways, the kinetic energy can carry on
for quite some time
Sometimes difficult to balance the forces of rudder and thruster:
Full thruster of 13t is only equal to kick ahead with dead slow

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

32. Lateral motion to starboard with kicks ahead
Same way as for a lateral motion to port.
Problem arise when the engine is reversed (see next slide)

33. Lateral motion to starboard with astern power
More problematic to starboard
(with single screw)
When astern power is applied
(to control headway):
bow swings to Sb
tendency to give thruster to
Ps will bring ships back to initial
position.
swing

35. Thrusting with sternway
pivot point moves aft : big turning lever for the thruster / possible to
steer the vessel with the bowthruster
beware for poor thruster power and sluggish response of vessel
avoid the development of a big rate of turn: difficult to control

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

37. Thrusting with sternway / Turning moments of propeller and bowthruster
Therefore it is possible to work the vessel astern by overriding
The effect of transverse thrust with the bow thruster.
→ It may often be preferred to back up a waterway or to a berth

38. Bowthruster at work

39. Working astern in a channel
Lack of experience ends up with the ship in a difficult position (pos6)

40. Working astern in a channel
The process of backing a ship up a waterway with the aid of a bowthruster can be dangerous:
The inexperienced can unintentionally allow the ship to become a victim of unexpected influence of transverse thrust and insidious drift
→ For this manœuvre, large ships use often the assistance of a tug secured aft to assist steering and positioning of the stern / the bowthruster controls the bow.

41. Position 1
Ship has entered the channel
Good position with bow canted to
port to allow for prolonged use of
stern power and transverse thrust

42. Position 2
Insufficient correction of transverse thrust → stern has dropped away from centre of channel
If propeller and thruster are now used simultaneously: lateral motion to port
this is not intentional and may be unnoticed

43. Position 3
ship steady on correct heading but off
centered
at this stage: use bow thruster vigorously / or: kick ahead with rudder to port to bring stern back to the centre of the channel

44. Position 4
Sequence of events in position 2 is
repeated → ship keeps drifting to port
On very large vessels, the kinetic energy keep the vessel drifting for a long time.
A light wind on the Sb side will increase the drift.

45. Position 5
The ship is getting too close to the edge and is running out of manoeuvring space
There is insufficient water to port to enable the bow to be thrusted to port

46. Position 6
The ship ultimately is hitting an obstruction on the port side.

47. To avoid this kind of manœuvre:
Get the ship moving smartly astern initially and keep it moving
Use kick aheads with caution: it takes the way off the ship which can drift out of position with leeway
No attempt in transverse winds overriding the thruster’s power
When sufficient sternway: stop the engine to avoid transverse thrust
Watch the heading carefully at all times and use thruster vigorously to keep the stern on the intended track / the rest will follow.

49. Working astern to a berth
The position of the pivot point: ships goes
slowly astern and turns to Sb.

50. Working astern to a berth
With engine ahead it is easy to correct a too high approach speed
or an unaccurate positioning of the stern

51. Working astern to a berth
With engine stopped and bowthruster in use: pivot point moves
after and bowthruster works on a large turning lever

52. Leaving a berth
Vessel turns around a pivot point situated forward: stern leaves the
berth
« 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 bow
leaves the berth

53. Leaving a berth
Small ships often use a combination of forward spring +
rudder + propeller + bowthruster

54. Backing in a narrow canal with beam wind
« Transverse thrust + bowthruster effect + wind effect » push
vessel to port: 2 tons of the propeller and 5 tons of the bow thruster
(pivot point between midships and stern).
This means a total transverse force on the ship of 7 tons to port

55. Comparison: Turning a vessel with little headway:
With bowthruster only
With a combination of bowthruster, rudder & propeller

56. Ship with headway / Using only the bowthruster
As soon as the ship starts turning, the pivot point will be situated somewhere between the stern and midships.
Although the lever of the turning moment is large, the effect will be very low, because :
1. the effectiveness of the bow thruster is very small
2. the effectiveness is decreasing rapidly with the ship’s speed ahead
3. there is high water pressure at the bow and consequently the lateral resistance of the ship is highest near the fore ship and is increasing with the speed. The bow thruster has to push the bow against the bow wave.
The consequence is, that at a forward speed of about 4 knots, the bow thruster is too weak to overcome the lateral resistance and to push the bow to starboard.

57. Ship with headway / Combining thruster , rudder & propeller
1. we first start by using only the rudder and the propellor: the pivot point moves ahead, between the bow and midships, the exact location depending of the ratio of the ship’s lenght to beam (L/B). The high lateral resistance at the bow, the bow wave, will now have a favourable influence on the turn.
2. Then, the bow thruster is started to starboard: it will increase the rate of turn, in spite of a short lever (pivot point ahead).

58. Twin screw ship + bowthruster
Crablike movement

59. New Designs

60. Anti-suction tunnel
Additional tunnel improves performance

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

62. K-Jet Altering the shape of tunnel apertures to improve the waterflow
through the tunnel and avoid
turbulences

63. Navyflux

64. With the help of a horizontal propeller, water is sucked up from underneath the vessel.
The vessel is manoeuvred by means of a 360 degrees rotating deflector, which turns the water through 90 deg. and forces it through a tunnel.
Veth-Jet bowthruster

65. maximum thrust can be achieved even at minimum draught, without any component parts protruding from under the ship. Thrust can be 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 vessel.
Veth-Jet bowthruster

66. Other application: Vessel blocked by ice

67. Other application: Purse seiner with bowthruster

69. Ship equipped with a stern thruster