Sharing experience.

Windlass on my B40 stopped working unexpectedly and for no obvious reason. Tested everything and all seemed to be good.

Had had the same unexplained fault on a previous Beneteau, to repair I connected the center ground connection on the control side of the relay to the battery stud in the bow rather than relying on the small diameter wire running back aft to the battery.

And - same again, like magic once this 6" wire added my windlass sprang back to life. The B40 is only  three years old, no obvious signs of corrosion or breaks in the wiring harness. Can only think this circuit is boarder-line from the factory and once a little life gets taken into consideration some resistance in the factory harness builds up and the relay simply won't work.

Would love to hear from anyone who might have insight into same and my non technical fix is troubling me!

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Replies to This Discussion


It seems like control relay failure. The control relay is mounted on the engine just behind the alternator (that's the case on B43).  It is a small box (aprox 2,5x2,5x2,5 cm) which is grounded to the dynamo. Check the cables; the yellow one might be loose or you need to change the relay. 



Thanks. Windlass relay on my B40 is in the bow in the forepeak under the fwd berth. I agree, yellow earth cable that runs back aft to the battery isolator switch seems to have a fault. Relay working fine since I provided a good ground / 0v return path.

Greg, Interesting. My 2008 B40 windlass has worked flawlessly.. but its a bit of a marina queen. 

Arne, Is this (green box) the windlass control relay? I assume this is what acts as an interlock to keep the windlass from working without the motor running?



That's the box I was thinking of. It's not the windlass relay, but the relay or switch that controls the feed of 12V to the control side of the relay under the berth in the forepeak. This is probably the weakest point of the windlass installation. If this switch fail, one can steal power to the control side of the relay under the berth from one of the bow thruster batteries. The windlass will then act as normal, but it should only be a temp solution.


I do have this little green box hanging off the back of my alternator. It's actually under one of the mounting screws. However, my windlass will run without the engine running so in my instance this thing does not sense power coming from the alternator before allowing power to the windless.
As I am still unaware of the root on my problem am not ruling this out, just still thinking it's a high resistance issue on the yellow control cable. (but happy to be proved wrong)

thanks Harry / Arne.

You've likely solved the problem. Although not tested it ould certainly appear that this "engine running" control relay is the faulty item. My wiring in a by-pass negative control line has proved all other items good, and obviously by-passed the requirement for the engine to be running. 

I had a fault on the alternator a month ago where the main +ve output stud nut came loose and actually fell off the stud altogether. Retained in the red boot, (clearly shown in the photo sent by Harry). Arcing destroyed the stud and I had to replace same. Possible that the windlass control relay suffered damage at this time. (NB, crimp on the +ve battery lead attached to this stud had a 3/8" hole, stud is 3/16", crap job by installer.)

Thanks for help both.

Had the windlass fail to operate a couple of years ago. All I go was a click like you hear on a car when the battery is dead. Found that the 300a fuse on the house battery had corrosion on the faces which caused enough of a voltage drop to prevent the windlass from running. There was enough juice to activate the relay which explains the clicking noise.


Bow thruster battery:

Battery is not getting charged by the charger or by the alternator.  Thruster does operate with the battery voltage at 10.1V reading on the volt meter.  I disconnected the positive and get 10.1v reading.  Also same reading when connected and charger is on.   A battery isolator is between the charger and battery.  I checked all fuses and breakers, all ok.  Is there a way of checking the isolator?

When you say you checked all the fuses and breakers did you check them with an ohmeter or did you read the voltage on the input then output side of each device? If you didn't do voltage checks recheck every connection, fuse, breaker, common terminals, components, etc. Best to start at the charger then work through every switch, isolator, fuse, etc.  You should see 12+ volts at the charger. Once you find the 10.1V then you've found the source of the volatge drop.

Good luck


All fuses and fusable links weere checked for thru voltage, 12 plus volts.  I placed a full charge on the battery and tested the fluid with a hydrometer and found one seal dead. Replaced the battery but still no meter reading that the battery is being charged by the on board charger. Could not find where the thruster battery is tied into the 110 charger.Maybe the thruster battery is charged by the engine alternator only.  Thruster will only operate when the motor or motor key is on.


The thruster only working with the engine turned on is normal, the windlass works the same way. I believe it's wired that way to keep people from running thier battery down if not connected to shore power. The 110ac charger is connected to all the batteries and according to the schematic the thruster battery is tied in to the charger via one of the isolators. If you're only getting 10.1V and the charger is on then there has to be a voltage drop somewhere. If you want to check the isolator just check the voltage from the charger at the input to the isolator, then output voltage from the isolator. You should have almost the same reading, maybe a couple of tenths lower on the output. Dont forget to check the connections on the isolator for looseness or corrosion. If you still cant find the problem call in someone for help, be it a friend experienced with boat electrics or a professional. I'd also contact your Beneteau Service Manager for their recommendations. Perhaps there is a unique manner in which the system works.

On my B43 (European model),the thruster batteries are only beeing charged by the engine alternator.



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