WBH wrote:

Hi,
For lightning protection, your keel should be connected to the mast, not to
the boat's ground.

These are not mutually exclusive
options, of course. Typically, the keel
is connected to the mast and to the
boat's "ground".

Isn't a fair amount of imagination
required in order to derive a benefit
from isolating the DC ground from the keel?

Disconnect the keel from ground and measure again.

If that can be easily done, it might
confirm the diagnosis.

Also, there are 2 schools
of thought about bonding all bronze thru-hull fittings.

There are some strange theories about
bonding metal thru-hull fittings as part
of a lightning protection strategy, but
from a corrosion perspective, the
science is clear.

A quality bronze thru-hull, unbonded,
and immersed in seawater may well
outlast a fiberglass hull! Bonding
(i.e., attaching) a bronze prop to a
stainless shaft is what creates the need
for a sacrificial anode in the first
place. If you hang the bronze prop over
the side on a rope, you will have to
wait decades before you notice any
corrosion. It won't propel the boat, of
course, but think of what you'll save on
zincs!


Recommended reading:
Nigel Calder.
Do you have a saildrive or a shaft?
Cheers,
Wout



Chuck

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