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Motor Boat Forum

Dual battery setup

by ChrisH » 16 Apr 2017, 22:29

Looking to install a second battery that I can run the stereo and 12v sockets off while at anchor. Thought I could get the 2nd battery on the opposite side to the current battery but turns out I can't quite squeeze it through the available gap past the engine. Current battery sits on the port side of the engine close to the outer wall of the hull. There is room to install the 2nd battery there too but will this make the boat too heavy on that side? Or is it going to be insignificant compared to the weight of the engine?

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by BruceK » 16 Apr 2017, 23:18

No its significant. Ballasting correctly is paramount and more so at speed especially if you have a steep rise at the stern. My boat is solid as a rock stopped or at low speeds. But above 25knts when shes riding the endge of the V if the wife walks from one to the other beam the boat will list to her movement if I dont alter trim and Im 8 ton all up and she makes less than 1% of that weight
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by Bigplumbs » 17 Apr 2017, 07:57

Chris

I was going to do this last year but in the end I did not want the extra weight. I decided to just use my main battery which actually has a lot of capacity a radio does not take much power and if you have LED lights in the cuddy etc those are very low usage

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by mlines » 17 Apr 2017, 08:00

Perhaps look at moving other items in the boat to achieve the balance?

The previous owner for ours put in dual batteries on one side of the boat and it rides just fine, however he also put the shower tank and diesel heater tank on the opposite side. We often run with the shower tank empty however and do not notice a trim issue. The diesel tank is very small (only a few litres, we hardly qualify for the minimum delivery quantity at the petrol station). Our boat does tend to run nice and flat in the water however, even with a single crew member on board (the batteries, helm position, heater unit, electronics etc are on the same side

Why not place the battery where you want and see what happens?
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by ChrisH » 17 Apr 2017, 09:06

Thanks all for your input. Martin I don't have much else to move around. We have no shower or heater. Literally hull, seats, dash, engine, fuel tank 140l and anchor. This is in a bow locker on the helm side. Battery stern on the crew side. I don't have many provlems with trimming currently but then there is not so much room to move around. Yes she will list a bit if some one moves from one side to the other, but it is more annoying than performance impacting I find.
Dennis how long can you run your stereo before you would start to risk being able to restart your engine?

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by Bigplumbs » 17 Apr 2017, 21:20

ChrisH wrote:Thanks all for your input. Martin I don't have much else to move around. We have no shower or heater. Literally hull, seats, dash, engine, fuel tank 140l and anchor. This is in a bow locker on the helm side. Battery stern on the crew side. I don't have many provlems with trimming currently but then there is not so much room to move around. Yes she will list a bit if some one moves from one side to the other, but it is more annoying than performance impacting I find.
Dennis how long can you run your stereo before you would start to risk being able to restart your engine?

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I have never actually timed it but I think you might be worrying too much. I also use my ipod to a Bluetooth speaker which gives quite a while and this is separate from the boat battery.

Try buying a small gell 12 volt batter and wire to your stereo and see how long that lasts a

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by Ianfs » 18 Apr 2017, 10:03

Most 4.3 engines have something like 80 - 110 amp hour starting batteries. I'm no expert but a car stereo probably draws about .5 amps and therefore at full charge in your starting battery and 80 amp hours you would be able to play your stereo for 160 hours before it goes flat. What I do know is that I have anchored for a few hours playing the stereo to no ill effect. I suppose a lot depends upon what you intend to plug into the 12v socket.

I like Dennis's idea of a smaller battery which may fit starboard and that you can get past the engine. :)
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by Bigplumbs » 19 Apr 2017, 05:48

Assuming you trailer you boat just do a test on the trailer. Turn the stereo on low volume for say 10 hrs and see if she still starts OK. I bet she will be fine

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by betty boop » 19 Apr 2017, 07:33

On our old boat we had 1 80A battery and the radio ran it flat very often (different batteries over 10 years) , mostly on the drive whilst cleaning etc. as I rarely used the radio on the water (engine off) for fear of getting stuck. The battery was always fully charged and in A1 condition. It occurred to me once in Shoreham with a flat battery that jump leads tend to be a bit short. The answer to that issue was a £50 glove box lithium battery starter (which matched the 3.0L merc).

In my experience of loud music and waiting for wives whilst they're shopping time off charge is limited. Even IF you run the experiment on land and you get 4 hours music there is nothing to guarantee it lasts that long 2 miles off coast and then you're in trouble.

Our new boat has 2 x140A batteries (upgraded by the last owner from 1x 100A ) that Im refitting today, squeezed into one port locker (hence the 4 hour refit time and aching arms :evil: ) Cant say I find it performance affecting but we have a central fuel tank this time and forward water tank so it may counter the extra.

hope that helps
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by ChrisH » 19 Apr 2017, 22:20

Bigplumbs wrote:Assuming you trailer you boat just do a test on the trailer. Turn the stereo on low volume for say 10 hrs and see if she still starts OK. I bet she will be fine

Dennis

Thanks Dennis. Bit actually keep her on a mooring on a drive on dock. So can't really do that.

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