House Battery Bank?

[Capt_Dana]

I have a 2003 480 Sedan with Cummins QSM11s...

I have not used my bow thruster since the batteries died 3 years ago.  I can't personally remove the big 8D batteries from in front of the engines and it is not worth the money to me to pay someone to do it. $300ish for new batteries and $400-$500 to remove old and install new ones.  All for a bow thruster that I don't need.

I am considering replacing them with smaller batteries wired to be a house battery bank.  Has anyone done something similar?  I hate that my house battery is also a starting battery. 

[wingless]

Yes it is possible to safely effect that modification.

Note that these changes must be properly implemented and should conform to ABYC, using appropriate materials and tools.

My suggestion would be to start w/ the existing wiring diagram, then plan the new system w/ a new or an updated wiring diagram.

The existing bow thruster battery bank is probably wired to provide 24V nominal output, instead of the desired 12V nominal for the house bank.

Note that the best battery configuration has identical batteries placed in parallel. Identical MFG, model and date code. When that is not followed, the currents are not balanced. There is more charging current going into one and more discharge current coming out of one.

One engine starting on the house bank is common and is no issue. The other bank is used the other engine and for helm electronics. This setup is nice because it permits redundancy. The emergency start permit quick / easy jumping the dead bank if it is dead. A fall back is the third bank for the generator and the AC/DC battery charger.

[CCH]

I would not recommend tying the bow thruster to a non exclusive power source. 1. It sounds like the only time you would be using the thruster is in some adverse condition where a failure of the thruster, or other systems would make the situation even worse. 2. The bow thruster pulls hard when in use. The draw and/or volt drop could cause other items on that bank to kick off or at the least cycle. Again this would be at a not ideal time, ie docking in a significantly adverse wind/current situation. For what it is worth, I consider the bow thruster an emergency item like a bilge pump or a fire extinguisher and service it accordingly.