I installed a galvanic isolator which in effect breaks the green wire
circuit for making this "battery", yet maintains the ground protection.
My zincs have not eroded as much since I did this.

"Jean Dufour" wrote in message You know
that, thru the AC ground lead, all boats plugged into the dock supply are
connected together. If you have an aluminum
prop and your neighbour, a brass one, you're making a battery together
even without problem in the dock wiring. Check if the
boats without problems are all equiped with a brass prop (or marine
stainless) and if those who have corrosion issues don't.
It's just a guess but if so, I don't think the problem is with the dock
wiring.

Best way to prevent that, in ANY cases, even if no apparent problems are
experienced, is not to leave the shore power cord
plugged while you're not aboard. If your batteries can't keep their charge
during the time you're not there, then it may be
time to replace them. Anyway, doing this while the marina checks its
wiring should prevent any further problems.

Jean Dufour
Montreal, Qc