An acquaintance had the same problem and painted, or partially painted
the boat several times - about once a year if memory serves. I asked
him several times whether he was sure that the hull was totally
isolated from the electrical system and he kept assuring me that it
was. His mate checked it!

After he had spent God knows how much money on yard costs he
apparently found another friend who repaired what ever problem was
leaking electricity and from what I hear (he's sailed for S. Africa)
is having no more paint problems.

I'm not a steel boat guy but I'd make very sure that the entire
electrical system IS isolated, radio grounds not forgotten and
remember that the engine has to be electrically isolated, *before I
started looking elsewhere.

Hi Bruce,

Thanks for that information. I'm happy to hear that I'm not the only
one with this problem. Ideally I would indeed like to isolate the
whole electrical system. Because what is happening now is that if
anywhere in the system a ground wire touches the hull, the return path
of the electricity goes through the sea water, to my prop, prop shaft,
engine and engine ground back to the battery.

Unfortunately, giving the starter and alternator a separate ground
connection is not an easy thing to do reliably. Therefore I'm now
thinking of connecting a separate wire from engine ground to the hull
(the engine isn't really ground. the resistance between hull and
engine measures 10 ohms). I think this is what is called 'bonding'.
WIth that extra wire, any leaking ground current can take an
attractive direct path back to the battery instead of going through
the sea water and creating expensive damage.

Any comments on this approach?

Thanks,
Joost