Russell wrote:
Thanks all. Here is more info. I called the harbor master's office.
They had a consultant test all the boats in the marina. Over 100 boats
were found to have the same situation as mine and we were all given ten
day notices, to correct, unplug from shorepower or remove the boat from
the marina. The test showed "power cord ground terminal grounded to
through-hulls". I am not sure how they tested, but isn't the same
ground connected to the shafts? And if the AC ground goes to the engine
DC ground post, as ABYC requires, and I assume all our boats comply,
then wouldn't the AC ground by definition then be connected to anything
on the ground strap which is everthing metal on my boat, including the
through hulls. This is all very confusing and seaches on Google bring
up a lot of data, but not a consensus. I would think, to comply with
the marina demand, we would all have to break any connection between
any metal in the water and the AC ground. But to do that, we would have
to remove the AC ground from the engine DC ground, and that is very
dangerous and violates ABYC and every other code. Any ideas?

chuck wrote:

Andina Marie wrote:

Russell wrote:

We have been eating up zincs, and just had to replace both props. Had
the marina check and they said the power cord gound terminals on our
twin inboard were grounded to the thru hulls. This is in sal****er.
Any ideas on what could be going on, why this is an issue and what to
do to correct it?

For safety reasons, the ABYC specifications call for the shore power
cord to be grounded to the DC ground

OK

which
includes the underwater

metal attached to the engine(s).


I don't think ABYC actually requires this part. It
is often done, but not always.

There is an increasing number of new boats that
are designed with electrically isolated props and
shafts. Without a connection to the shore power
ground, there is little chance for galvanic
currents to be set up with a neighboring boat. In
fact, even through-hulls can be electrically isolated.

It is actually a safe and trouble-free approach,
but it requires an insulating shaft coupler. And,
of course, some special attention to an RF ground,
if there is one. Usually a capacitor with high
reactance at 60 Hz can effectively isolate the
grounding plate.

Chuck


Your cheapest protection is a galvanic isolator. They are on sale for
under $100 at Defender
http://www.defender.com/product.jsp?path=-1|328|303336&id=605562
One isolator can handle a 50 amp shore cord or two 30 amp.


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Yep - It has already been recommended above:

Install a galvanic isolator

Conceptually, you cut the green wire just as it comes aboard, and insert
the galvanic isolator between the cut ends. Make no other changes
aboard your boat.

If you don't have one, then your zincs are protecting the dock, the
pilings, the electrical conduit, etc, and all the other boats in the marina.

bob
s/v Eolian
Seattle