PM Series: PM Task – Service Bow & Stern Thrusters


Whether you have hydraulic or electric thrusters, they both are susceptible to failure due to lack of service as they are typically difficult to access and often forgotten about until the wind is blowing you into a piling and they either don’t perform or under perform. Hydraulic thrusters are usually installed on larger yachts and commercial vessels and are often rated for continuous duty while electric thrusters may only be run for a few minutes or less at a time. Once of the first signs that you may be overdue for a system inspection is a drop in performance. This can be caused by marine growth in the tunnel and on the propellers, loose or leaking electrical or hydraulic connections, or a weak power source such as dying batteries, failing hydraulic motor, or slipping PTO drive.

Electric thrusters will almost always have a dedicated battery located near the thruster bank due to the high amperage load of the thruster motor. This intermittent heavy load, along with constant vibration puts extreme strain on the electrical system. Any weak link in the system such as worn motor brushes, loose electrical connection, or a weak battery can make the system inoperable or worse, cause a short.

Photo courtesy of Steve D’Antonio

“Thrusters are often installed in locations with poor access and as such their maintenance needs are frequently overlooked. The brush dust visible on the outside of this thruster motor is a signal that it’s ready to be cleaned and inspected” says Steve D’Antonio.

Sidepower Aft Fuse

Electric thrusters demand very high amperage during their operation.  Make sure all connections on the main fuse, batteries, and thruster are tight and in good condition.  A spare fuse should be carried for remote cruising.  A blown fuse is a sign of a poor connection, motor binding, or other problem that should be identified and repaired before returning to service.  The fuse indicated above was the incorrect size for the fuse holder and created a high resistance connection that could have caused a serious fire.  Routine inspections should reveal problems like this before they cause a problem.

The connection and driving link between the motor and the gearbox typically is a shear pin or torsion sleeve. These units are designed to fail if the propellers become seized in order to protect the motor and gearbox from damage. When traveling in remote areas you may want to consider carrying a spare torsion sleeve and shear pins.  These can be replaced without hauling the boat  to complete the repair.

Photos courtesy of SidePower

The gearbox on your thruster may be sealed as it is on the Side-Power SE 250 TC or it could have gear oil that should be checked and changed  at the interval recommended by the manufacture (usually three years). Gearboxes that require service will always have a header tank that is supplying oil to the gearbox and acts as an indicator if the oil is leaking out or water is seeping in.

The low oil indicates a leak in the system.

Routinely inspect and clean the propellers and thruster tunnel of marine growth.  For safety, isolate power to the motor and tag out the thruster controls.  During haul-outs, thoroughly clean and paint the tunnel and gear leg to reduce marine growth.  Remove and clean the propellers by scraping and light sanding, and then paint.  Over time propellers will wear and knicks will appear on the edges – replace propellers and drive pins as needed.

Regular inspections and proper maintenance will ensure that your thrusters will be available when they are needed.

About our “Preventative Maintenance (PM) Series”

The PM Series addresses a PM found on most vessels by highlighting the requirements for a specific piece of equipment and then expand on equipment variations and techniques.  While you may not have the specific equipment referenced in the PM Series, the concepts should apply to your equipment.  The PM Series presents actual PMs taken from the WheelHouse Maintenance Management System.  WheelHouse users will always have the PMs and related documents and parts that are specific to their equipment.  Non WheelHouse users  should refer to their manufacturers guidance for your specific equipment when completing maintenance.  Contact WheelHouse for a product demonstration and pricing information.

Posted in Maintenance Log.