Hi, You might, or not, be interested in some small scale experiments I
did when a child.
Using 1.5 volt hobby motors, and having already set up a container of
salt water for some oxygen and hydrogen experimemts, I immersed a
running 1.5 volt dc motor under the salt water. It ran for quite a few
minutes, I got bored, and upped the volts from around 1.5 to around 4.5.
The result was green foam and steam. When I reached 12 volts, the motor
lasted only a few seconds.
Any immersion or splashing might not kill the motor. We have to assume
that you would be running at lower volts, within the design range for
the motor. From the green foam I had, I assume that there was some
serious electroplating effect going on that was degrading copper parts.
I think a key question would be whether the motor continued running or
not.
If not, then basically it would be the same as any other item made of
dissimilar metals that is immersed in salt water. I suspect that if this
is a high risk, it might be prudent to attach isolating switches to all
electric wiring, so that any electrolysis can be averted. Then the only
(Really?!) issue left would be galvanic action.
Another variable would be the time spent wet with salt.
I personally, if having had this occur, would strip the motor into basic
parts, and flush with clean fresh water.
You could look into chemicals that neutralise salt, we have them here in
Canada for cleaning winter road salt deposits off floors. I don't know
what they are made of, or whether they just give cosmetic results rather
than chemically neutral ones.
You would probably be better leaving the parts slowly flushing rather
than drying out, until you have some neutralising method arranged.
From my industrial experience, there is also some special varnish that
motors have over the windings, and that are tested using a 'megger'
device, that I believe tests for conductivity across the surface of the
varnish or whatever. You might need to do preventive maintenance ahead
of time by going with a whole load more varnish - it is special
dielectric varnish, I believe. This would allow subsequent flushing with
less risk.
The real key to operation offshore might be to make the boat so that the
motor does not get wet. This might be possible by enclosing it, and have
shaft seals. A fan making the enclosure have positive pressure might
assist.
An inverted plastic box that will prevent the water rising up to the
motor is another possible way.
Or make the sealing more local, if the heating of the motor permits, by
covering the motor directly. Close it in, and feed dry air to it.
Dunno if this helps,
John
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