Adding extra battery to bow thruster battery bank or replace single battery?

davethedog

davethedog

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Our 41ft sailing boat has a 8hp sidepower bow thruster fitted, but compared to friends os ours (who have a 37ft yacht with a similar thruster) ours seems very weak.

I have checked the current single bow thruster battery (12V 100Ah 800A) and it gives 12.7V with no load and then 9.5V under the thruster load, so is this correct? It is charged via the Alternator and shore power by the way.

So, do you think the current battery is dead, or is it worth adding another battery to the bow thruster bank to increase the capacity?

DTD
 
davethedog said:
Our 41ft sailing boat has a 8hp sidepower bow thruster fitted, but compared to friends os ours (who have a 37ft yacht with a similar thruster) ours seems very weak.

I have checked the current single bow thruster battery (12V 100Ah 800A) and it gives 12.7V with no load and then 9.5V under the thruster load, so is this correct? It is charged via the Alternator and shore power by the way.

So, do you think the current battery is dead, or is it worth adding another battery to the bow thruster bank to increase the capacity?

DTD
Click to expand...

The battery isn't really big enough, fit two.
 
How is this battery charged? Direct link to another bank or though a charger, diode, splitter, FET, etc?? That's also a substantial voltage drop whilst under load. Does it recover immediately or take a while to "come back up".

When doing warranty work for Fairline who also use Sidepower among others, they (not sure if that's Fairline or Sidepower) mention 10% as being an acceptable voltage drop.

Also as the voltage drops, the amperage across your brushes increases and things start to wear quicker or stick, melt or snap.

Can you get a clamp meter suitable for DC loads (beg, borrow or steal) and test what is being pulled?

How old is the thruster? When was it last serviced?



davethedog said:
Our 41ft sailing boat has a 8hp sidepower bow thruster fitted, but compared to friends os ours (who have a 37ft yacht with a similar thruster) ours seems very weak.

I have checked the current single bow thruster battery (12V 100Ah 800A) and it gives 12.7V with no load and then 9.5V under the thruster load, so is this correct? It is charged via the Alternator and shore power by the way.

So, do you think the current battery is dead, or is it worth adding another battery to the bow thruster bank to increase the capacity?

DTD
Click to expand...
 
Thanks all and a few answers:

Not sure when the thruster was last serviced but another thing to add to the list.

Current battery is a Banner Powerbull model.

Ref the charging, not sure as need to investigate this as there is an ACR in near the battery charger and assume it leads to the bow thruster battery.
 
An 8hp thruster takes a hell of a current. Your single battery isn't up to the job, and may be approaching the end of its life. Better to fit 2 decent batteries, and you need to investigate how they will be charged.
 
davethedog said:
Our 41ft sailing boat has a 8hp sidepower bow thruster fitted, but compared to friends os ours (who have a 37ft yacht with a similar thruster) ours seems very weak.

I have checked the current single bow thruster battery (12V 100Ah 800A) and it gives 12.7V with no load and then 9.5V under the thruster load, so is this correct? It is charged via the Alternator and shore power by the way.

So, do you think the current battery is dead, or is it worth adding another battery to the bow thruster bank to increase the capacity?

DTD
Click to expand...

You do not say exactly which Sidepower thruster you have but looking at their website I see 750 CCA batteries recommended for their 8.4 hp thrusters.

An 800 CCA battery will just about be up to the job when new but perhaps not once it is past its prime.

If its off load volts is 12.7 after resting for 12 hours or so it indicates that it is charging OK but 9.5 volts on load is not brilliant. Check all the connections. Perhaps check for volts drop between the battery terminal posst and the thruster ( negative as well as positive) If no excessive volts drop perhaps get the battery load tested but be prepared to accept that is getting past it.

Fit a battery with more CCA to replace it. Perhps by fitting two slightly smaller ones in its place because a bigger battery than 100Ah is a heavy lump to handle.
 
hi, my thoughts, for what they are worth, are that there are probably a number of factors that will effect the performance of a bow thruster, boat windage, distance from pivot point, tunnel size etc. However, it certainly sounds as though the size of your thruster (6kw) is more than adequate for a 41' boat. Battery seems as though it is good at 12.7 volt, that is if the reading was taken some while after it was last charged. Obviously once a heavy load is applied the voltage will collapse, 9.5 volts is perhaps a bit low, if you could get this up to 10.5 volt I would have thought that you would see a distinct improvement in performance. You don't say where the battery is sited in relation to the thruster, or what size cables are being used, this could have a bearing on the performance of the unit. Imho you should look at the system as a whole, I have recently been through a similar exercise with my own boat, albeit somewhat smaller and for an electric windlass not a thruster. Once the motor is engaged it will draw current from wherever it can, therefore with adequately sized cables you should be able to get some extra "oomph" from the alternator and the domestic battery bank. After all, your only likely to be using the thruster with the engine running. Also worth checking that you don't have any unnecessary voltage drop due to poor connections etc.
 
Thanks all and thinking a bigger CCA battery may be in order and will clean and check all the connections etc also.
 
pawl said:
hi, my thoughts, for what they are worth, are that there are probably a number of factors that will effect the performance of a bow thruster, boat windage, distance from pivot point, tunnel size etc.
Click to expand...

My thoughts as well. Are you comparing the performance between boats on speed of turn or, wash from thruster? As others have said, the on-load battery voltage is low and I would be tempted to borrow a second battery and connect in parallel with jump leads to see the difference in performance.
 
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