Best batteries for domestic/bow thruster

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shortjohnsilver

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I need to replace my batteries.
Recently had the occasion to use the bow thruster and had a massive drop in available power. So much so that the chart plotter indicated the drop to below 9.7 V just before it powered off and the bow thruster struggled. Engine running as manoeuvring into berth.

The thruster is linked to the domestic bank - two 110Ah in parallel. Separate starter 80Ah.

Ive owned the boat for eight years and the batteries have always managed very well and supported by solar.

I rarely use the bow thruster but this day the wind and tide through the berth was causing a problem. No worries, a bit of bow thruster and we’re all good. However, bow thruster kicked in and then performance dropped considerably. Looked to my new chart plotter and saw the volts dropping rapidly, then shut down at 9.7 V.

I suspect that the batteries need replacement and ask what batteries are best for the domestic bank. I’ll probably change the starter battery too.

Should I consider a dedicated battery for the bow thruster or remain with things as they are. I don’t really want the chart plotter and other instruments crashing every time I blip the bow thruster, or will the new domestic batteries retain sufficient capacity, that that does not happen? I did have the fridge on but as said engine running.
Ta Si
 
Firstly I would double check that your batteries are fully charged.
How many seconds of thruster did you use?

I suspect that if you've been happy with the setup for the past 7.5 years, then replacing pretty much like for like would not be a bad option.
8 years is a long time for any battery.

I think with any thruster set up, you need to test it now and then to be sure the batteries will still deliver what you might need in the worst case?

Or has the thruster always spanked the batteries down to 9V, and the real problem is your new plotter not being very tolerant of low supply voltage?
OR a bit of both?
There was a thread recently about using a small battery to protect the plotter/GPS from this sort of thing, but it degenerated into the usual; 12Both piffle.
 
If you have owned the boat for 8 years and everything has been fine, i'd replace with like for like.

If you felt a need for an "upgrade" you could fit an AGM battery at the bow. Connect the existing cables to it and new cable from the battery to the thruster. You would need to fit appropriate fuses/breakers at the new battery to protect the cables going to the domestic bank and the thruster.
 
My thruster/windlass battery is linked to the engine start battery not the domestic one. That's because it's the same sort of battery on the grounds that running a thruster or windlass is akin to running a starter motor.

That way both of them get involved in starting the engine and both get involved in running the thruster/windlass. Since the engine is always running when the thruster or windlass are operating, they're never going to be depleted to the point that I can't start the engine, although in that event I could cross-link the domestic bank.
 
It’s possible that the batteries always dipped when I used the bow thruster and I have been ignorant of this in that my old Navman chart plotter remained on and I had no idea of the demand voltage, assuming that all was well.
Initially it was only that on this occasion the bow thruster seriously lost performance just when I needed it, that I thought, oops batteries cant handle this and happened to see the plotter go down and saw the voltage dropping below 9.7 V

Mostly, I don’t use the bow thruster and when I do it really is just a blip either way, usually. Actually maybe I do more often than I admit! But never for prolonged spurts.

I think that I’ll replace like for like as recommended by you guys, including the starter battery.

I‘m interested in your suggestion Paul regards introducing another battery to support the bow thruster demand. So, would that be a dedicated battery - stand-alone or linked in parallel to the domestic bank? I mean by doing that would it increase my overall Ah capacity from 240 Ah and therefore also benefit from the solar too?
 
Catalina 36 that’s ideal.

I believe that my windlass is connected to the starter battery similarly as the engine has to be running to use the windlass, which is fine and I get that.
The bow thruster must have been retro fitted and connected to the domestic bank - as indicated by the voltage dropping out at the chart plotter, which is on the domestic side, clearly.

Right, new batteries required and take the power for the bow thruster from the starter battery as you have. Starter battery also topped by Solar.

Any recommendations regards suitable batteries?

Thanks gents. Just need to find a competent marine electrician to do this as I’m totally useless when it comes to this sort of thing.

Si.
 
shortjohnsilver said:
I‘m interested in your suggestion Paul regards introducing another battery to support the bow thruster demand. So, would that be a dedicated battery - stand-alone or linked in parallel to the domestic bank? I mean by doing that would it increase my overall Ah capacity from 240 Ah and therefore also benefit from the solar too?
Click to expand...

For the occasional use of the bow thruster i'd connect it in parallel to the domestic batteries. You already have heavy cables going forward, so just shorten those and connect to the new battery, with a new pair of cable going to the thruster. The existing cables will keep the thruster battery charged up, take advantage of the solar power, provide an extra boost to the thruster and should eliminate much of the voltage drop at the electronics end.

For various reasons, i tend to connect the windlass to the engine battery, unless it too has a dedicated battery. Some installations have dedicated batteries at the bow for thruster and windlass, either stand alone (with split charging to keep them charged up) or in parallel with one or other battery banks. Several ways to do it, none essentially right or wrong. In your case, given the current setup, the above makes best sense to me, as it increases your domestic capacity as well as giving the thruster a boost (partly due to the added available power, partly because it's closer to the battery).
 
Many thanks - I’m away and frankly the domestic batteries are struggling too much. I intend to follow PaulRainbows suggestion as above, but I would like to change the two domestic batteries Imminently.
I have Vetus 2x120 cca 780A with reserve cap 25A 230min whatever that means.
Can I replace with bigger batteries say 2x180,s or do I have start thinking about new alternators?
 
shortjohnsilver said:
Many thanks - I’m away and frankly the domestic batteries are struggling too much. I intend to follow PaulRainbows suggestion as above, but I would like to change the two domestic batteries Imminently.
I have Vetus 2x120 cca 780A with reserve cap 25A 230min whatever that means.
Can I replace with bigger batteries say 2x180,s or do I have start thinking about new alternators?
Click to expand...
If you have room for 180ah batteries, i'd fit them, no need to change the alternator, unless it's especially tiny. What output is the mains charger and solar ?
 
Ok so everyone is different. I use an Optima 80ah battery very near to the windlass and bowthruster.
I have a domestic battery, an engine start battery and the bowthruster battery ie. 3 banks. they are charged via a Sterling no voltage loss black box.
When I buy an engine start battery, also an optima, the old one becomes the bowthruster battery, as it is not so critical. This way I get a new engine start battery every 4/5 years.
The engine start battery is connected to nothing else!
I do get voltage drop when using thruster or windlass, but not below 11.5v and only momentarily
 
Thanks PaulRainbow, I’ve seen some Varta LFD 180 Ah that will fit dimensionally that indicate 1000 CCA will these be suitable?
If they’re good enough I’ll order online ASAP.
I have also seen some Platinum 180’s that look okay.
The charger is a Dolphin 50Hz 20A unit and the solar panels SunWare 36W panels x 2 regulated by a SunWare Fox-350 unit.
Thanks for all the advice everyone. This forum really is good stuff.
 
shortjohnsilver said:
Thanks PaulRainbow, I’ve seen some Varta LFD 180 Ah that will fit dimensionally that indicate 1000 CCA will these be suitable?
If they’re good enough I’ll order online ASAP.
I have also seen some Platinum 180’s that look okay.
The charger is a Dolphin 50Hz 20A unit and the solar panels SunWare 36W panels x 2 regulated by a SunWare Fox-350 unit.
Thanks for all the advice everyone. This forum really is good stuff.
Click to expand...

The Varta batteries are fine. The mains charger is a bit under spec', should be a 40a really, but see how it goes.
 
HowardClark thanks and that fits with my plan. To get through the remaining season I’ll change the domestics as above and later introduce a dedicated battery to assist with windlass/bowthruster as per PaulRainbow’s recommendation.
My current domestics are shot and use of the thruster crashes the voltage to well below 10V and anchoring using the windlass will no doubt be problematic too
Many thanks to all.
 
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