Richard,
I have replied to other similar threads over the years and sometimes people
listen and others do not, but I will repeat this advice again. Never connect
anything electrical to your hull, including a ground connection. If your
hull is not earth referenced, you will never suffer damage from a hot berth.
The cure is simple. Additionally, if your service DC is 12 volts, install a
red lamp in some location that is always visible and connect a 12 volt lamp
between your ship's battery to the hull. If your hull ever becomes shorted
to electrical earth, the lamp will be on indicating a short circuit
signaling you to take immediate action to resolve the fault.

The solution is simple on a boat you build, but isolating your hull when
someone else built it, can be a nightmare. No matter how much effort this
takes, the peace of mind this brings is worth it.
Steve

"richard" wrote in message
ups.com...
Same boat, same marina for 5 years-slightly different slip this year.
Boat stays in water 8 months out of the year (Boston harbor). always
have mechanic change zincs when winterizing (he says he did so this
year). discovered the prop had been destroyed by electrolysis as well
as damage to engine trims. never seen anything like this before
pulled boat our and had mechanic put new zincs on. Cost for haul,
wash, new zincs, labor and put back in water-$500 plus the cost of
replacing the prop. mechanic and I decided not to wait on engine trims
can anyone tell me more about what to do about the electrolysis? does
anyone think that this is something that could be covered by
insurance. have never made a claim on any of my boats over the year so
have no clue
thanks