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fritzdfk · 30-05-2017, 06:43

I just removed the round zinc on my rudder today. It is a circular zinc bolted to the rudder plate with zinc on both sides. The rudder has stainless bar welded to the plain (or at least magnetic) steel blade. The blade and shaft are in good condition except for the area of the blade under the zinc. That area is very pitted and perhaps half eaten away. The boat is new to me and is 35 years old so perhaps this is to be expected or is it?

boatpoker · 30-05-2017, 06:46

What kind of boat and what waters do you sail in ?

fritzdfk · 30-05-2017, 07:26

Quote:

Originally Posted by boatpoker

What kind of boat and what waters do you sail in ?

Fiberglass boat, salt water, Alaska. I bought the boat last fall and it had been out of the water for 8 years or so. Prior to that it had been kept on a mooring or anchored for quite a while. It is 35 years old so older history is unknown. No other corrosion problems.

Sailmonkey · 30-05-2017, 07:56

So the rudder is steel?

fritzdfk · 30-05-2017, 08:01

Quote:

Originally Posted by Sailmonkey

So the rudder is steel?

Yes steel. The shaft is stainless steel (non-magnetic) and the blade is magnetic steel.

boatpoker · 30-05-2017, 08:03

Quote:

Originally Posted by fritzdfk

Yes steel. The shaft is stainless steel (non-magnetic) and the blade is magnetic steel.

If that is true, you have a galvanic cell and a perpetual problem.
I find it hard to believe this is OE.
I have never heard of this construction on an FRP boat.

fritzdfk · 30-05-2017, 08:26

Quote:

Originally Posted by boatpoker

If that is true, you have a galvanic cell and a perpetual problem.
I find it hard to believe this is OE.
I have never heard of this construction on an FRP boat.

I don't think a steel rudder is unusual on a FRP boat.

boatpoker · 30-05-2017, 08:46

Quote:

Originally Posted by fritzdfk

I don't think a steel rudder is unusual on a FRP boat.

I'm sitting here typing up my 4,563 survey report and have not seen one on a sailboat yet. Some TT's, yes but never seen one on a sailboat.
If you know of any I'd love to hear about it.

Aside from that any steel/stainless steel or austenitic/martensitic stainless steel weldment is destined for failure and only the most ignorant builder would do such a thing.

fstbttms · 30-05-2017, 08:48

Quote:

Originally Posted by boatpoker

I have never heard of this construction on an FRP boat.

Very common on powerboats.

Cheechako · 30-05-2017, 08:50

A lot of stainless is magnetic. If it has been work hardened and not solution heat treated after, it's magnetic. It's a fiberglass boat with a steel/ss rudder....?