electrical problem

[gasdok007]

Have an electrical leak(DC 12 v.) in an aluminum hulled boat. I am trying to troubleshoot. Should there be any continuity between the negative ground and the metal hull? If I hook a test lamp to the positive battery post and to the hull I get a circuit., even with all negative wires pulled off terminal blocks sequentially.Possibly a dead short somewhere?I dont get any change in the lamp when I pull all the fuses from the positive side either. The boat has no AC input and is out of the water and dry.

[Ike]

No, you should not have continuity between ground and the hull. ABYC does not recommend this, although I've seen it done. It generally leads to bad galvanic corrosion. Not just you, but also every boat around you. Also If you do have AC it can result in a severe shock hazard if you get a ground fault, which is what you have.

You are simply going to have to check every ground on your boat. If no luck there, take a look at the engine and make sure the engine mounts isolate the block from the hull. Generally the block is the ground and if the engine is not isolated from the hull then you'll get continuity.

[Ike]

Just another quick thought. If your boat has a bonding system, that is disimilar metal through hulls bonded together by cable, then that is probably connected to the boats ground. You don't need that ground connection on a metal hulled boat. Remove it.

[gasdok007]

Have isolated problem to the honda outboards.The negative ground to the engines completes the circuit thru the hull,any thoughts?There may be a problem with how they were rigged, port ignition must be on in order to start starboard engine, and it is the port battery that drains even with battery switches off.

[Ike]

Are the engines mounted direcctly to hull? Or is there some insulating material between the engine and the transom or engine bracket? Is there a ground wire in the cable that runs from the engines to the controls and what is that ground wire hooked up to. I'm not familiar enough with how the OB mfgs ground the electrics on the engine, or if they ground it at all.

Maybe someone else on this forum that knows about rigging OBs, can help you

[MikeJohns]

Gasdok, Peter

To bond or not to bond? The debate can be very complex. Don't take ABYC views as difinitive there is a lot to this subject.

I like a bonded system on a metal boat, it ensures that the hulls anodes remain the anodes in any self generated electrolysis. So for example your isolated outboard leg doesn't get sacrificed by an external current to save your hull zincs (...It happens).

As for electric shock you should be using an isolated supply on a boat !

In this case it sounds as though the outboard starter motors are not isolated devices but have the same setup as a motor vehicle. No great problem. Dont go disconnecting bonding straps they may well be there because an expert has recommended them ! For example there may be an active protection system at work.

Also don't confuse galvanic (no external imposed current) with electrolytic (external imposed current).

Hope this helps