Russell wrote:
Since my post a few days ago, spoke to our marine electrician and the
on-staff electrical expert retained by the Harbor office. We are going
to have to install an isolation transformer in our dock box. This will
cost about $1,000 after parts, labor and some mods to the box. All 90
boats in our harbor that got the notices have to do this, move, or
unplug or disconnect the AC ground from the DC, not a good option.
So, now I see the West Advisor says that apparently solves the marina's
issue with the AC, but unless we separate all the underwater stuff,
like the through hulls, we still are subject to DC corrosion. Can this
be true? What is the real solution to the AC, the DC, the safety and
the corrosion problem? Is there one? We are one of 90 modest boats from
about 28-48 feet, mostly 1970's through 1990's vintage. We all have to
get these transformers now, but the issue is what else do we need to do
once we are on the transformer?


Well, the way this has happened concerns
me, as I said before. That you are
required to purchase the transformer
makes the situation even worse (except
for whoever is making a $90,000 sale). I
know of no precedent for an action of
this sort by a marina.

It is really too bad, because it is
fairly easy for an unskilled technician
to determine which boat(s) are causing
the problem.

Regardless, the transformer will solve
the corrosion problem ONLY if the
secondary hot and neutral are connected
to nothing on land. No grounding on land
whatever. You then will use the neutral
wire onboard as both neutral and ground.

The corrosion problem I'm referring to
is one in which an unprotected vessel
near yours obtains protection from your
zinc using the AC grounding conductor as
the return path. There are obviously
other corrosion problems, some quite
serious, but the isolation transformer
will do nothing to protect against those.

You will still need a zinc to protect
underwater props, etc., but that is
almost always under your complete
control. Except in very unusual
circumstances, if you install proper
sized zincs and check them from time to
time, you should have no further
corrosion problems. A technician can
even show you how to make simple
measurements to check on whether your
protection system is working.

To summarize: yes the transformer will
completely eliminate what it appears is
causing your corrosion problem based on
what you have described. I don't believe
the isolation transformer will introduce
any new problems at all, other than the
cost.

Hope this helps, Russell.

Good luck.

Chuck

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