Galvanic Corrosion 1977 Supersport

[jackball42]

I recently got a 1977 Supersport with a Merc 140 and the outdrive and hull look they are suffering from galvanic corrosion. The outdrive is pitted and the V part of the hull has some corrosion on it. This boat does not have the Mercathode system. I thought someone had the boat in salt or brackish water but think its galvanic corrosion. Is there anything I should check to find the source of the current flow? The anodes are intact. If the charging system has an issue can it cause this? I wonder if the previous owner had the boat in a marina hooked up to shore power. I dont know the history of the boat.

 

[barato2]

Re: Galvanic Corrosion 1977 Supersport

first place i'd go is to check that there is no path where the grounding can go to the hull. charging system itself shouldn't cause this but if there are issues that let it ground to the hull, i think that could. shore power leakage can definitely eat a boat...i bought a lot of parts from a guy whose steel hull sailboat died exactly that way

 

[jackball42]

Re: Galvanic Corrosion 1977 Supersport

Are you saying the engine should be electrically isolated from the hull?

 

[ezmobee]

Re: Galvanic Corrosion 1977 Supersport

That boat was obviously stored in the water. If you aren't going to be storing it in the water, I would clean it up and not worry real hard about more future damage.

 

[paparoof]

Re: Galvanic Corrosion 1977 Supersport

Are you saying the engine should be electrically isolated from the hull?

Yeah I'd like some clarification on this point too. Last time I tested it, I have continuity between the engine block and the hull.

 

[MichaelP]

Re: Galvanic Corrosion 1977 Supersport

I had the same issue with my hull and the pitting went through in a couple spots. The motor that came with it is newer and has no signs of corrosion. Mine was definately in salt and could have had a ground to the hull too. Ended up sand blasting the bottom only to get it all nice and clean and stripped the sides by hand. Its not recommended to sand blast aluminum but the bottom is so well supported that I didn't get any warping and I didn't baby it either. Proceeded to fill the worst pitting with marine tex and primed with a high build epoxy primer. More details in my resto thread. You can fix this.

 

[jackball42]

Re: Galvanic Corrosion 1977 Supersport

I dont plan on storing this in water. The worst may be a week when I go fishing in Canada next summer. Most of the time it will be put back on the trailer after each use.

 

[barato2]

Re: Galvanic Corrosion 1977 Supersport

Are you saying the engine should be electrically isolated from the hull?

to be honest, gents, i was just guessing and talking out of my {rear end? league? depth?} as i read Papa's response, i realize it ain't feasible to isolate an I/O electrical system from the hull, probably not an OB either.

Jackball, you might try just adding a zinc anode to outside of hull if you seem to have more problems. but i don't think you'll have to worry about it if it won't be in water for long, and fresh water at that.

here's info from someone smarter than me:
http://www.yandina.com/electrolysis.htm

 

[Pugetsound]

Re: Galvanic Corrosion 1977 Supersport

I would for sure isolate the Motor from the hull. Take all your electrical wire to a isolated block and the same with the Grounds. The boat I think should be grounded only from the battery or an isolated grounding block. The best for the hot side is a block with fuses in it so each item is free from any contact with the Hull.

 

[jackball42]

Re: Galvanic Corrosion 1977 Supersport

After further investigation I think this is salt corrosion. I pulled the outdrive off and there was a bunch of white stuff in the water hole on the bell housing. I took the whole outdrive apart and bead blasted everything and gave it a new paintjob. Replaced all the rubber while I was in there too along with the trim switch. What a fun job that was.

 

[elkhunter338]

Re: Galvanic Corrosion 1977 Supersport

I keep zincs on the outdrive bolts and the zinc rudder on the outdrive above the prop, also have a 2 zincs in my engine cooler. The salt water eats these things up but I show no galvanic corrosion on the boat. I have to replace about every 6-8 weeks in the water. I only use it 3-4 weeks a year so every other year new zincs.