Rudder head corrosion

[aflanigan]

The rudder head on my Helms 24 which is presumably aluminum alloy exhibits pitting corrosion at its lower edges, presumably below the water line. I recall reading that aluminum doesn''t do well submerged because it cannot form a protective oxide coating like exposed aluminum. I guess this is why the bottom part is corroded (and underneath the stainless steel straps of the pintle bolted to the sides of the rudder head, there is also a whitish powdery crud).

I am wondering if a zinc chromate primer would be a good barrier coating to prevent any further corrosion on the rudder head. I have disassembled it and wire brushed down to bare metal as well as I could. Any thoughts?

[DelmarRey]

My suggestion would be to sandblast the affected areas, fare them in with epoxy with a filler, then paint with epoxy paint as far up as need be to keep it out of the water. And the same under the SS pintles. Tape off an area around the pintles and paint under them. SS tends to speed up the corrosion process when mated to aluminum (electrolysis). Or you could just paint the whole rudder in epoxy, If you want to go that far................Del

[peterpan2k]

You might considder bonding this to your zink when you get it repaired to stop further loss.
Jim

[GordMay]

Zinc Chromate primer will not provide an effective barrier between the Aluminum and Stainless (as you note,neither of which do well under water); but Del''s advice presents a good start.
Even better would be a nylon sleeve, separating the dissimilar metals (perhaps not practical?).
Further to peterpan2k, If the pintle fastenings are accessable from the inside, bond them and the rudder shaft, if possible, (using a shaft brush) to the ground bus.