Galvanic corrosion?

[Sarge]

I have a aluminum deep Vee hull which is one year old. I purchased a snap-on boat cover option for it. This winter, I took the cover off and found that practically all of the snap studs that were screwed into the aluminum had a quarter-sized corrosion spot under each one that lifted the paint from the hull. The paint has blistered and there is a white powdery susbtance under each one. Is this because of a stainless steel/aluminum metal reaction or some other problem? What is the cause and a possible solution? The stainless eye bolts on the transom used for tie downs were unaffected as were all of the stainless cleats.

[RANGER]

When two dissimilar metals come in contact with each other they begin to cause a corrosive event, not unlike a battery. This holds true for nearly all metals. HOWEVER, Stainless Steel (SS) is, probably, the least composite metal to cause the corrosion you are discribing. I didn't have it with my aluminum boats and SS snaps - are you SURE they are SS snaps?

[JerryA]

I would suspect that you have a bad ground or electrical current getting into your hull through an exposed wire somewhere. Are any of your electronics malfunctioning? Prime suspects are the bilge pump and the AM/FM radio/antenna. The corrosion is showing up first in the main area where dissimilar metals make contact - all the screws on your snaps. You might have a dealer who is familar with this type of problem check your boat over with a very sensitive volt meter. If the source is not identified, the corrosion will get worse and appear in other places. Unfortunately, the only way to repair the damage already done is to remove the snaps, take it down to bare metal, prime and repaint. Apply silicone to the screws when reinstalling them. Tough problem - good luck.