Bow thruster maintenance checklist

Thrusters are low-maintenance, not no-maintenance. Most of what goes wrong with them is preventable: an anode that wore away, a prop full of barnacles, a battery that quietly died over the winter, or a lug that loosened and started to cook. The good news is that the whole routine fits into a haul-out and a few habits.

This checklist follows Sleipner's and Vetus's manuals. Always check your own model's manual for anything specific to it.

Every time you use the boat

• Main switch on, panel on. Turn the thruster's main switch on when you board. On Sleipner panels, both ON buttons are pressed together.
• Short bursts. On/off DC thrusters are built for short use. Sleipner puts maximum continuous use at about 3 minutes, after which a thermal cut-off shuts the motor until it cools.
• Engine running while maneuvering. Sleipner recommends keeping the engines running when using the thruster, which helps keep battery voltage up. With a dedicated thruster battery on its own charger, it also starts each trip full.
• Main switch off when you leave. Sleipner says to always turn the thruster's main switch off when leaving the boat.

During the season

• Check the battery. Sleipner's table puts a charged 12V battery at about 12.7 V at rest. Below 12.3 V, recharge it or replace it before trusting the thruster. If your thruster battery has its own charger, glance at the charger's status lights.
• Look in the compartment. It should be clean and dry. If there is water, find the source. Sleipner and Vetus both want the motor kept dry and well ventilated.
• Nothing stored around the motor. DC motors get hot. Sleipner notes the motor can exceed 100°C before its temperature switch acts, and says not to store lines, sails or gear in the thruster compartment.
• Carbon dust. Brushed DC motors shed a little carbon dust. Keep the area clean and separated from stored items.
• Notice changes. Weaker thrust, new noises, or the thruster running in short bursts are early warnings. Our troubleshooting guide covers what each one means.

At every haul-out (before each season)

Underwater

• Replace the anode before every season or when about half is gone, per Sleipner. Use thread glue or sealant on the holding screw. In some waters an extra anode is needed to last between lifts.
• Antifoul the gear leg and props. Never paint the anode, rubber seals or the prop shaft, and keep paint out of the tracks where the prop hub runs.
• Clean and coat the tunnel. Growth in the tube costs thrust. Thin primer and antifouling only; no thick build. More in our antifouling review.
• Check the prop. It should be secure on the shaft, with the drive pin in place, and turn freely in the tunnel. Look for chipped blades.
• Look at the tunnel ends. Damage or flaking at the hull joint should be repaired before launch.

Inside

• Motor bracket bolts tight, per Sleipner's seasonal list.
• Electrical connections clean, dry and tight: battery terminals, fuse holder, switch and motor lugs. Discolored lugs or melted heat-shrink mean a connection has been running hot.
• Gear oil where applicable. Sleipner says most of its gear legs are pre-filled; legs that are not pre-filled need periodic oil changes.
• Brushes on brushed motors. Sleipner's troubleshooting table lists loose brush springs as a cause of low performance. Brushless motors like Vetus's BOW PRO skip this item.
• Battery condition. Sleipner notes that thrust drops as batteries age and returns to normal with new ones. Load-test the thruster battery and replace it if it is tired.

Winter or long storage

• Keep the thruster battery charged. A smart charger with a maintenance mode handles this; discharged lead-acid batteries suffer in storage.
• Main switch off, and the control panel off.
• If the boat stays in the water, plan for a diver to check the anode mid-season in warm water.

Extra items for retractable and hydraulic thrusters

• Retractable units need an annual inspection of the deploy mechanism and hatch; Sleipner provides a guide for its models.
• Hydraulic thrusters add oil level and condition, filters, hoses and fittings. Vetus asks owners to keep hydraulic oil under 100°C in use and to carry out the specified maintenance regularly.

Signs that need attention now

• Thrust noticeably weaker than last season. Check battery voltage and growth first; both are common and easy to fix.
• Clicking without the motor turning. Usually low voltage at the solenoids. Do not keep retrying.
• Motor spins, bow does not move. Likely a broken drive pin. Stop running it; Sleipner warns that running the motor without prop load can seriously damage it.
• Water in the thruster compartment. Find the source before it reaches the motor.
• Hot or discolored cable lugs. A high-resistance connection that will get worse.
• Thruster won't stop. Main switch off immediately, then have the solenoid checked.

Each of these is covered in detail in our troubleshooting guide.

Quick reference

Next step

If you would rather have the haul-out items done for you, or something on this list looks wrong, our thruster repair and service team covers anodes, props, seals, motors and electrical faults on all the major brands. Book a service visit around your next haul-out.

Questions people ask