So our bow thruster is acting up again and I now have a clear picture of the symptoms.

We have a brand new battery that is working great. When I turn the thruster on it works just fine.The trouble starts as soon as I increase the throttle on the engine.Then, the thruster shuts off.

In fact, I paid attention to the led light inside one of the buttons, which signals if it's on. Turns out that when it is, as I rev up the engine the light starts to flicker until it goes off signaling the thruster died. I bring the engine back to idle and press both buttons and the thruster turns back on normally.

It's as if the engine running fast draws the power AWAY from the system when it should actually be the opposite, don't you think? More engine, more power being put out by the alternator...

Of course I thought about the possibility that the alternator is putting out too much power overwhelming the system but wouldn't that trigger an immediate shut off (like a fuse going off) instead of slowly removing power as the flickering suggests?

This has been happening since very early on because I can't even remember the last time I heard the beeps announcing the normal automatic shut down of the thruster after 3min or so.

Wondering what you think could be happening here...

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Franc, our 43 has a Max-Power thruster which has a thermal fuse. If I run the thruster too much, like when trying to dock in 20kt winds, it can overheat and trip the thruster. When it does it beeps as a warning then shuts off. I have to turn it back on by holding both buttons as normal. I wonder if you have the same setup and if so it's causing the issue. I also seem to remember someone with a 40/43 having a similar problem a couple of months ago. I'm afraid I can't recall the solution.


Interesting one, as you say this is the opposite way round and i think there is a separate regulator for the front batteries, it would be interesting to monitor the voltage across the batteries from idle to higher revs so that a regulator/battery fault could be ruled out.

I just checked the manual for a Max Power which is what I have and while it makes a comment about low voltage there is nothing about it being too high. They do have a control box which may be sensitive to voltage levels, both high and low. It may be worth doing a voltage check on it at various rpms to see if there's a correlation.


The bow thruster on our Euro built Oceanis 43 (Hull 341) failed last week without any warning from the buzzer or the flashing indicator light indicating the thermal fuse was switching.

A quick check with the multimeter revealed the negative high capicity switch under the V berth was open circuit; I assume from too high a current laoding. A further check revealed the positive switch had previously been replaced with a much higher capacity switch. As we purchased our vessel from a Beneteau  dealer who had used her as a demonstration yacht it must have been they who carried out the first repair.

A look at the original equipment part revealed it was only just up to the load of 250 amps of the thruster which led to me replacing it with a 350 amp unit.

Perhaps this fault could be the underlying problem the members have met and in their case when the switch cools down it agains works for short intervals only.

Hopefully this may assist,


I have Max Power on my 43 and I have a 450 amp unit (original from the factory).

Thanks for all your answers. I have experienced the overheat beeps so that's not it. A friend suggested that perhaps the vibration of the engine is causing the switch at the helm to disconnect from a faulty wire but I would expect that to happen less consitently. I guess I must do that voltage check after all...

Our bow thruster went off at the weekend, luckily it was the fuse so started to hunt about on the web - £30 for a direct replacement, £12 for a replacement from the dealer (425A) or £4 from an electrical retailer (radio spares)

Beneteau have changed my fuse .... I had the same problem. The reseller from Maxpower told us that the orgial fuse mounted by beneteau was net the one they recommend .... After long discussions and angry they accepted to change it ... since then ( i think now the fuse can hold a whole city ) i newer had problems with it 

Hi Franc

The auto shut off is after around 20 minutes.

I would check that the voltage at the cables in the thruster or batteries do not get over 14,8V or so first.

I would also check for some item overheating with a thermometer ( infrared Fluke ) for example.

I just got the Raymarine TH24 and I am starting to explore this sort of use also with it.


Might be an alternator failure. Bow thruster shuts off when alternator, for some reason cuts off charging. It's same with windlass. Both are switched to alternator operation to save batteries. There are cases alternator stops charging at high RPMs. I diagnosed this failure several days ago, and still searching for the reason.

Jumped on the boat the other day and my Maxspeed thruster would not work at all. The unit turns on and the light stays on, but pushing either button has no effect. I had the control board go two years ago, but the symptoms were different, thruster would only work in one direction. The thruster worked the day before, go figure. Quick check of the battery was good, no issues there. Looking for troubleshooting advice on this one.



High amperage systems like windlasses and thrusters operate with both low and high amperage legs. The low amp side is used to activate a relay that engages the high amp side. You'll need to check both sides of the circuit to find the problem. Always start with the simple things first. Like the switch, relays, battery posts and any other connection that could possibly become corroded. Note that corrosion is not always readily visible to the eye. Also look for pinched or cut wires just to be thorough.

Start with the simple stuff first. Remove and clean the cables from the battery posts. (I've had the windlass fail to work because of corrosion on the connection)

Check the fuse at the thruster. Do voltage checks on both sides, it should be the same. If not then check/clean the connections. 

Not sure if there's a fuse on the low voltage side of the switch but if there is make sure it hasn't blown. Also do voltage checks at the thruster relay. When the button(s) are pressed do you get voltage at the relay? If so do you get it on the output side of the relay?

You'll have to work your way through the circuit (which you should find in the wiring diagram) until you find the problem. A sure fix is to spend large sums of money on a non returnable item. Once you do that you'll assuredly find the problem is something simple.

Good luck and let us know what you find.


October Moon #001


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