Bow thruster troubleshooting

When a thruster acts up, it usually does it at the dock with an audience. The good news is that a short list of causes explains most faults, and you can narrow it down with a multimeter and a few minutes. This guide goes symptom by symptom, based mainly on Sleipner's and Vetus's own troubleshooting tables.

Safety first: turn the thruster's main battery switch off before touching anything near the motor, solenoids or prop. An accidental start with hands near moving parts causes serious injuries. On the hard, never run the thruster for more than a fraction of a second, and let the prop stop completely before reversing.

Panel won't turn on

• Sleipner: both ON buttons must be pressed at the same time. Panels also switch off automatically after a period without use.
• Vetus BOW PRO: press the on/off switch a second time within 6 seconds, with the joystick centered. If the joystick is off-center at power-up, the panel will not activate.
• Everyone: main switch on, control fuse intact, and battery voltage present at the thruster. Vetus also lists a separate CAN bus power fuse on BOW PRO systems.

Panel is on, nothing happens, no click

If the solenoids are not even trying to engage, Sleipner says they are probably not getting a run signal from the control system. Check the control cable plugs at both ends for corrosion or a pushed-back pin, then work back toward the panel. A professional can test the thruster's solenoids directly at the thruster to tell a control fault from a thruster fault. If it works from the thruster end but not from the panel, the fault is in the panel or the cable between them.

On Vetus BOW PRO, the controller LEDs tell you a lot: separate indications for overtemperature, overcurrent, battery voltage too high or low, a blocked motor, and general errors.

Clicking, but the motor won't turn (or runs in stutters)

This is the most common call we get, and it is almost always voltage. The click is the solenoid engaging. When the battery voltage collapses under the motor's load, the solenoid drops out, voltage recovers, and it pulls in again. Sleipner calls this solenoid flapping, lists low voltage as the most probable cause, and describes a thruster that runs about half a second every 4 seconds as a symptom.

What to check, in order:

1. Battery at rest. Sleipner's table: about 12.7 V for a charged 12V battery. Below 12.3 V, recharge or replace before testing further.
2. Voltage at the thruster while running. Measure between the motor's main terminals while someone operates it. Below about 10.5 V on a 12V system (21 V on 24V), the thruster will not make rated thrust; Sleipner says below roughly 8.5 V it will not operate correctly.
3. The path in between. Main cable size versus the maker's table, every lug, the fuse holder and the main switch. A connection that is warm after a run is the culprit.

Sleipner's IPC (Intelligent Power Control) detects flapping and stops trying to run the thruster to protect the solenoid contacts. If yours does that, fix the voltage problem rather than resetting and retrying. Our fuses and cable review covers cable sizing.

Motor runs, but no thrust

If you can hear the motor spinning and the bow does not move, the drive between motor and prop has let go. Common causes:

• Broken drive or shear pin. Vetus lists a drive pin broken by an object in the tunnel as the cause, and says to replace the pin and check the prop hub for damage. Max Power sells replacement propeller pins by tunnel size, such as part 312053 for its 185 mm props.
• Prop loose or missing its key. Sleipner's table says to re-fasten or replace the prop and/or key.
• Flexible coupling disengaged between motor and drive shaft, on Sleipner units. It needs refitting correctly before the motor goes back on.
• Gear leg failure. With the motor removed, turn the drive shaft by hand and feel whether the prop shaft turns. Sleipner recommends replacing a failed gearhouse rather than rebuilding it.
• Damaged blades from debris, per Vetus.

Stop running it as soon as you notice. Sleipner warns that running the motor for more than a few seconds without prop load can seriously damage it.

Weak thrust

• Low voltage, as above. This is the first suspect every time, and aging batteries are a common cause; Sleipner notes new batteries bring performance back.
• Growth on the prop, gear leg or inside the tunnel. Barnacles on the prop are especially costly.
• Weed or fishing line wrapped around the prop, per Vetus.
• Brushes on brushed motors. Sleipner lists brushes with no spring tension as a cause of low performance.
• Cavitation from a tunnel too close to the surface or with sharp ends. Symptoms include noise, high current draw and reduced thrust. Sleipner's fixes are tunnel depth, rounded ends or proportional control.

Stops after running a while, works again later

That is the thermal protection doing its job. Sleipner's SE motors have a thermal cut-off that switches off an overheating motor and resets automatically once it cools. Maximum continuous use is about 3 minutes, and over time the thruster can run roughly 10% of the time. Vetus BOW PRO units reduce output as the motor or controller heats up, so you see thrust fade rather than a hard stop.

If it happens during normal short docking bursts, look for a cause that makes the motor work harder: low voltage, growth, a dragging prop, or a compartment with no ventilation. Holding against a strong wind for minutes is a sizing question; see how to size a bow thruster.

Runs in one direction only

Most on/off thrusters use a solenoid pair, one per direction. If one direction works and the other does not, suspect that side's solenoid coil, its control wire, or the panel switch for that direction. Sleipner's table describes checking continuity through each solenoid coil; no continuity means the solenoid needs replacing.

Won't stop running

Turn off the main switch. A solenoid contact can weld closed. Sleipner's IPC and older microprocessor controls are designed to stop the thruster on solenoid lock-in, and its table suggests that with the main switch off, a light tap on the solenoid may release it; if it stays locked, replace it. Do not keep using a thruster that has done this.

Wireless remote not working

Sleipner's checklist: transmitter battery, power at the receiver, and pairing between them per the manual. Then check that the wired panel works, which tells you whether the problem is the remote or the thruster.

When to call in help

Battery, connections, fuses and growth are owner-level checks. Solenoid testing, drive pin replacement, gear leg and motor work usually mean the boat out of the water and the right parts on hand. Sleipner asks owners to note measurements before calling a dealer, which speeds things up. Our thruster repair service covers diagnostics on all major brands; send us the symptoms and your readings and we will tell you what we think is going on before we roll a truck.

Questions people ask