Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.