Electrical Grounds

Hello,

Well, the past owner of my boat didn't do me any favors. He told me the wood in the transom was recently replaced. A year into owning the boat, I begin seeing small, powdery pinholes popping through the aluminum transom (boat is a 1989 20' Mirrocraft Voyageur). Searching for answers as to why, I stumbled upon this site and discovered the PO used pressure treated plywood against the aluminum. Repeat after me..."DON'T USE TREATED WOOD IN AN ALUMINUM BOAT." The old wood came out (stubbornly, as the wood and aluminum corroded themselves together), and I just picked up two 3/4 in sheets of marine ply, ordered through Menards for $60 ea. I have also taken this opportunity to install some Bennett trim tabs and clean up what was once a rat's nest of wiring buried deep within the bowels of this vessel. With all the pumps, lights, trimtabs, etc, I have a bunch of ground wires to connect. The previous owner had a million ground wires going right to the battery, so I fabricated a bus bar out of stainless screws tapped into a small piece of 3/8 aluminum with a single cable going to the neg battery post. This bus bar was, in turn, screwed to the underside of the aluminum splash well. A good idea, or so I thought until someone pointed out I might cause further corrosion by having the battery grounded to the hull. Should I redo my setup or keep on truckin'? The boat is used in freshwater and spends most days up on the trailer.

Re: Electrical Grounds

Remove it and place wood between the boat and the bar.

Screw the bar into the wood and make the wood a little longer on each end and than attach the wood to the boat same location if you like.

Don't let the screws, bolts, touch the bar and the boat and your good to go.

Re: Electrical Grounds

agree. i have been tell people not to use PT Wood, for years.

Re: Electrical Grounds

There is a product electricians use for aluminum wire. It is a gel that keeps oxidation from occurring. It is required on all connections in service panels where aluminum is used. Grainger sells it. It works very well on battery posts also.

Re: Electrical Grounds

Ayuh,...

I used PT in mine, but that was Before the chemical changes...

Anyways,...
I Agree, you should isolate the ground from the hull...

Even though the motor,+ drive are grounded to the battery,+ are mounted to the hull,...
Everything else Electrical should have it's Own ground path back to the battery...

I made a mistake with a little light acouple years ago,+ had little Pits showing up anywhere thepaint was scratched,+ wet...
Electrolisis will turn your boat to Dust in no time...

What are you going to do about the damage on the inside of your transom,..??

Re: Electrical Grounds

I have worked on boats that had a chassis ground like a car, it makes a real mess.

You should have a closed system.

On my boat I have one large ground wire that runs the length of the boat and anywhere I need a ground I just tap into it, works really well, but yes seperate your ground from the boat.

Re: Electrical Grounds

Thanks for all the input so far.

I will place an insulator between the grounds and the hull, then check with an ohmmeter to make sure it is isolated. As far as the holes in the transom are concerned, I caught it before it became a structural problem. I cleaned off the corrosion real well, and then have a friend who is very good at welding aluminum check it out. If he can weld the holes I will have him do it. If not, I will try something else. Possibly JB Weld, or some other epoxy. Or, perhaps someone else has another suggestion. I have gotten tons of inspiration from reading this board and it is one of the ways I while away these cold winter days.

Re: Electrical Grounds

If you ran a continuity test between the negative terminal of the battery and the hull of the boat, even though there are no chassis grounds, you will find continuity. Why? Because the engine is bolted to the transom and the engine block is ground -- hence there is a ground path from the engine to the hull and the negative terminal of the battery.