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?


Hello Russell,

I assume this is a relatively recent problem that
isn't correlated with any change(s) in the boat or
its surroundings that you are aware of.

A very common problem is that a nearby boat with a
depleted zinc is obtaining protection from your
zinc via the marina shore power cable (the green
grounding wire, specifically) as the return path.

If so, you can protect your zincs from this
"theft" by installing an isolation transformer or
a galvanic isolator. A third solution is to
isolate your boat's prop and shaft from the shore
power grounding wire. Of course, "pulling the
shore power plug" will solve the problem albeit
while adding a new one. Might be a good precaution
though until the source of the problem is identified.

There are other, less common, problems that could
cause sudden and rapid depletion of zinc (and props).

If you want to pursue it yourself, get a copy of
"The 12 Volt Doctor's Practical Handbook" from
West Marine or BoatUS. It's all in there. Not
really very difficult and there's no danger of
"breaking something".

But if you have more money than time, hire a
marine electrician or corrosion specialist. Get
the book in either case, since it costs a lot less
than a single zinc.

Good luck.

Chuck

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