Last spring I took up a bit too soon on the new through hull nut for
my Knotlog sensor and set it a bit below the surface of the hull.
Attempting to make lemonade out of lemons and kill another bird with
the same stone while excelling at creative writing by avoiding trite
sayings, I cut a ring of copper flashing and epoxied it to the through
hull surface thus:

http://home.maine.rr.com/rlma/Strider0604.htm#Copper

I took the sensor out for the first time today to check it and there
is not a hint of slime or growth on it. Last year it had small mussels
with discernable shells growing on it by August.

I think this really works. I wonder if there is some way to copper
sheath a fiberglass hull?

I know taking it out more often and putting it in a fresh water with a
bit of bleach is another approach but mine was cleverly installed so
that the fastest swap with the blank plug still results in a jet of
salt water all over the cabin sole and some drawer hardware. It's
enough of a clean up that I'd like to not do it more than a couple
times a season.

--

Roger Long