Bow/Stern Thruster
The fixed tunnel thruster: a propeller inside a transverse tube through the hull, pushing the bow or stern sideways. Unlike the retractable azimuth unit, it gives thrust in one axis only but has no moving seal exposed to the sea.
What to check on a Bow/Stern Thruster.
38 models from Brunvoll in Bow/Stern Thruster. Below: the full model list.
What makes this type
The standard bow or stern thruster is a propeller mounted inside a fixed transverse tunnel that runs through the hull below the waterline. Water is drawn in one side of the tunnel and expelled the other, pushing that end of the ship sideways. Unlike a retractable azimuth thruster, it produces thrust along a single axis only, either to port or starboard, and cannot rotate to give thrust in other directions. In exchange it is mechanically simpler: there is no strut to raise or lower and no rotating pod seal exposed to the sea, which makes it the lower-maintenance choice where full azimuthing capability is not required.
Legend
- right-angle gearbox
- drive motor
- hull, transverse section
- propeller
- tunnel through hull
- bar screens protect the tunnel openings at each end
Main components
Tunnel
A steel tube built into the hull, with rounded or flared openings on each side to reduce flow losses and cavitation noise as water passes through.
Propeller
Fixed-pitch or controllable-pitch, driven directly or through a right-angle gearbox from a motor mounted vertically above the tunnel inside the hull.
Read the full guide
Drive motor
Electric motor on most vessels, sized for intermittent duty since thrusters are typically used only during berthing and manoeuvring rather than continuously.
Seals and shaft
A shaft seal where the drive shaft passes from the dry motor space into the tunnel, the main point where water ingress can occur on this type.
Selection / Sizing
- Thrust output in kN, sized against the vessel's windage area and the manoeuvring performance required in the expected berthing conditions.
- Tunnel diameter, set by the propeller size needed to reach the target thrust without excessive tip speed and cavitation.
- Fixed-pitch versus controllable-pitch, trading mechanical simplicity against faster, smoother thrust response.
- Duty cycle rating of the motor, since most vessels use the thruster in short bursts rather than continuously.
Typical faults
- Shaft seal wear — slow water ingress into the motor space, often first noticed as bilge alarms near the thruster compartment.
- Propeller damage from debris drawn into the tunnel — vibration and reduced thrust, sometimes an unbalanced shaft.
- Motor winding failure from intermittent duty overheating — total loss of thrust on that unit.
- Corrosion at the tunnel grating or flared openings — increased flow noise and reduced thrust efficiency over time.
What to look for in a supplier
- Thrust and current draw figures verified against the vessel's actual electrical supply capacity.
- Seal design and access arrangement for replacement without drydocking where possible.
- Match to the existing tunnel dimensions if the unit is a replacement rather than a new installation.
Check the tunnel grating for debris and marine growth before every port call that will rely on the thruster; a partly blocked tunnel loses thrust long before the motor shows any sign of strain.
Models in this type.
The best-documented model of each manufacturer first, then the next — 38 of 38 models in Bow/Stern Thruster. Every row links to full specifications, documents and service notes.
Manufacturers.
All 19 manufacturers with models of Bow/Stern Thruster. Names with a manufacturer page open it; the others open a search across the full library.
All manufacturers in the libraryAlso in Bow/Stern Thrusters.
The other equipment types in this category.
Write to us about this model — the answer comes by e-mail.
Name the make and the model and what the job is: a spare, a service call, a second opinion on a data sheet. We answer by e-mail.
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Questions that come up with this equipment.
Is Bow/Stern Thruster data free?
Yes. Every model page, every guide and every datasheet for this type is readable without an account. An account adds saved searches and requests, nothing is taken away.
My model is missing — what now?
Send us the nameplate. We identify it by hand, add it to the library, and if you need a part or a service, the request is already on our desk.
Can you source a Bow/Stern Thruster part?
Yes. Tell us the manufacturer, the model and what you need — a person reads every request and replies by e-mail.