Bow thruster batteries on Beneteau oceanis

[LJScott]

We have owned our Beneteau Oceanis for three years. For all that time, after modest use of the bow thruster, we get a battery alarm. This occurred at new boat hand over, and they said "don't worry about that, it's nothing". We worry about it.

Has anyone else seen this problem, and what did you do to fix it?

Thanks,

[blue otter]

I have a 2yr old Oceanis . This may not be the same situation but worth a look......the only time I had a battery alarm go off.....the dealer had set the engine idle rpm to low and engaging thr thrusters draws a ton of juice and the low rpm drops the charge rate to low the alarm goes off ........800 rpm is the number......

[poiu]

I don't understand why boat builders feed bow thrusters with their own battery. Given the massive current draw in relation to their capacity, the peukert number will result in them not being much use. Especially so if the battery isn't in perfect shape and charge and is a flooded type. The house battery on the other hand will be much less effected by the large draw. It also is weight where you don't want it.

Maybe your issue in in the battery state, could also be an incorrectly set alarm. The bow thruster will drop voltage to low levels temporarily even in good batteries.

[SteveInMD]

On my 2016 Oceanis 45 I have two batteries mounted next to the thruster. I use it every time I leave from the slip or return because I have to rotate the boat 90° (it's a tight spot). I have never gotten a battery alarm.

I think you should use a multimeter to watch the battery voltage before, during, and after using the thruster. Do the same at the thruster motor to see if you have excessive voltage drop through the cables. This should help determine if you have a charging problem, wiring problem, or just need more battery capacity.

[LJScott]

Technicians just left. Their view is that all batteries are fine, but that temporarily, the bow thruster pulls more power than the alternator can supply, and we get a temporary alarm. This goes away once the alternator has caught up. Based on what we experience, this explanation sends reasonable.

We appreciate your insights.

[nigel1]

Might want to look at increasing the size of the charging wires. Beneteau would have used the minimum they could get away with.

[basssears]

Originally Posted by poiu

I don't understand why boat builders feed bow thrusters with their own battery. Given the massive current draw in relation to their capacity, the peukert number will result in them not being much use. Especially so if the battery isn't in perfect shape and charge and is a flooded type. The house battery on the other hand will be much less effected by the large draw. It also is weight where you don't want it.

Agree totally!

Originally Posted by poiu

The bow thruster will drop voltage to low levels temporarily even in good batteries.

My guess is it's this... in the Beneateaus we've chartered, regardless of battery charge level / capacity, when the windlass is going the voltage available to your alarm is going to be much lower (because of the temporary draw of the windlass) so it will alarm, when the windlass is shut off the voltage comes back up. But of course then you have to reset the battery alarm

[YachtBroker]

I was a Beneteau dealer for 19 years and this was a common problem. It is exactly what the technicians said, the draw is too great that it's dropping the amperage below the min set amount and the alarm goes off. Same reason why on most Ben's you can't run the windlass without the engine running.

[Myknjul]

I have a 2014 Oceanis 45 with the same issue. When I go to reset the alarm it shows I'm still at 12.7v. The beeping is quite annoying.

[SteveInMD]

Originally Posted by LJScott

Technicians just left. Their view is that all batteries are fine, but that temporarily, the bow thruster pulls more power than the alternator can supply, and we get a temporary alarm. This goes away once the alternator has caught up. Based on what we experience, this explanation sends reasonable.

We appreciate your insights.

But the purpose of the batteries located at the thruster is to allow for the short term massive current draw. Then the recharge can happen slowly over time. If you get an alarm I would think you need to increase the size of the bank at the thruster. Otherwise you are being hard on both the thruster and thruster batteries by running both at a lower voltage than intended. It seems to work correctly in the 2016 boats.

[SteveInMD]

Adding a battery is probably less expensive than the massive cables that would be needed to pull power from the house bank since it is far away.

[Nadezhda]

I have an engine battery bank and a house battery bank. Both have two batteries at a total of 300ah each. The engine batteries are rated to give more amps ooomph to start the engine, run the windlass and operate the bowthruster. The house batteries are more deep-cycle. We have half a ton of copper between the engine batteries and the bowthruster and have only ever had issues when the engine batteries were end-of-life

[LJScott]

Thanks everyone... You've helped us understand the problem.

[JOHNMARDALL]

The thruster battery should be as close as possible to the thruster and dedicated to the thruster and the windlass, each on its fused circuit. Thruster amperage requires very large and expensive power cables, and the longer they are, the more heat and energy loss will be created. I suggest putting a multimeter in voltage setting across the terminals of the thruster battery and then have a crew member operate the thruster. Resting the battery should be at around 13 volts and the voltage should not drop by more than 2 volts when the thruster turns on. If you're much outside of those parameters, the battery is probably shot. The alternator does not put out enough power to have any significant effect on the thruster - all of that short term burst of current must come from the battery bank. This needs checking because low voltage while the thruster is operating will cause premature failure of the solenoids. If everything checks out, then the alarm may be just a quirk of the system, but I wouldn't bank on that.Let me know if you need more information
Good luck
John Mardall
Vetus Maxwell Group

[SaltyMetals]

Interesting. I hv a Jeanneau 43ds which has a bow-thruster with its own batteries alongside the thruster and I suspect is very similar to the Oceanis. What is surprising is that both the 3 X 110 Ah service batteries and the 1 X 110 Ah engine battery were replaced after 8 years but the two smaller bow-thruster batteries are still going strong and are now 12 yr old.