b393capt wrote:
Chuck,

The copper wire I was referring to is entirely unrelated to the
fish. What I was doing is comparing the reading I would get from
connecting the zinc fish to boat ground vs. connecting a bare (at the
tip) copper wire in the water to boat ground. (in both cases with my
meter inbetween measuring current). My expectation is that by looking
at a change in voltage and current, I could learn something about
what's going on. E.g. while I do measure a current with the fish,
maybe the fish is inducing it. Now that I have the readings ... don't
know how to interpret.

My keel is iron and ideally has a succesful barrier coat of paint
between it and the salt water, as I know the keel is connected to my
boats grounding system (lightening protection). I also have a rudder
that I don't believe is tied into ground, but I am not sure. So is two
or three points under my boat creating a battery ... is the only two
points between the prop and my fish ?

Dan



Hello Dan,

Sorry for my misunderstanding about the
copper wire. And sorry to lead you on a
"fishing" trip.

So with the meter between the fish and
the copper wire dropped into the water,
you measured about 0.8 volts? That's
what you should be getting with that
arrangement.

I hadn't even thought about the keel.
Somehow I thought it was lead. But if
the fish is protecting an iron keel,
that could explain the 40-50 mA as well
as the 0.127 volt measurement. It would
also explain the accelerated erosion of
your prop zinc.

Theoretically, the barrier coat ought to
protect the iron keel, as you said, but
it is not unusual for zinc anodes to be
welded to it anyway.

It may be worth having a corrosion
technician check things out in person.
Email analyses tend to by awfully
hypothetical as you've seen. You might
also contact the builder to see if they
have a recommended fix.

Meanwhile, the fish is probably a good
measure to take some of the load off of
your prop zinc.

If the rudder is not bonded to the
boat's ground system, it's not likely to
be affected by, or affecting, the fish.

Chuck

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