Due to a small vibration problem - a three bladed prop which suddenly
became 2 and a bit - I've got my boat on the slips. This is a 60's vintage
21 ft clinker "motor launch". I'm fitting a re-worked second-hand prop,
new shaft, skeg bearing. Re-fitting the strange copper pipe arrangement
through which the shaft runs up to a copper plate under the in-board
stuffing box. Soldered together in-situ. And re-aligning the engine. And
replacing the 8 SS bolts which fastened the stuffing box assembly. It's
amazing how much water come in when three well corroded 3/16" bolts decide
to part company at once. This is a most unplanned period of maintenance, and
I need to get the boat of the slips quickly, work commitments take me
overseas at the end of next week. The slips are "free" as part of a club
membership - but others need to use them too. Re-slipping the boat later to
do some of this properly adds no cost. I have no choice but re-do the
antifouling. I've a shopping list for tomorrow as long as your arm. It
includes canvas and red lead ....

I can repair the damage, I'm pretty sure the root cause was electrolysis not
prevented by the main zinc - the skeg bearing insulating the shaft / prop /
stuffing box area. Adding a shaft zinc should fix that. But I'd like to
reduce the corrosion on the steel components. This includes a steel pipe
along the bottom of the keel, the skeg assembly, and the rudder. All of
these have survived decades in fresh water and a few years in salt, they are
severely pitted under the anti-foul. I'm not able because of time
constraints to blast everything back to bare metal and apply some high tech
coating. I can either just put on another coat of antifouling and do it
properly in 18 months, or make a slight improvement now if the effort and
time can be kept right down.

I'm thinking of angle grinder with wire brush removal of old paint and
corrosion products. This will not be anything like clean metal, the pitting
will leave paint and other stuff on the surfaces. Then brushing on either
straight epoxy or epoxy / filler system ( I've got colloidal silica or
graphite available). Then amine removal, and antifouling. Remember the
alternative is to just wet sand the old antifouling and re-coat. So I'm
after some feedback on using epoxy as a corrosion barrier. Given the time
constraints I can't do a better job of surface preparation, I can't spray
any fancy coatings. So is my idea even worth the effort?

All constructive comments within the next day or so most welcome - after
it's a done deal.

David

On Thu, 13 May 2004 21:07:55 +1000, "David Flew"
vaguely proposed a theory
.......and in reply I say!:
remove ns from my header address to reply via email

corrosion is usually due to oxidising, not reducing....

Due to a small vibration problem - a three bladed prop which suddenly
became 2 and a bit - I've got my boat on the slips. This is a 60's vintage
21 ft clinker "motor launch". I'm fitting a re-worked second-hand prop,

************************************************** *****

Sometimes in a workplace you find snot on the wall of
the toilet cubicles. You feel "What sort of twisted
child would do this?"....the internet seems full of
them. It's very sad