Stainless Keel Bolts

[AJAWATER]

I have recently taken on the restoration of a 1936 Elkins Yawl. The boat is generally sound but has suffered damage to the keel after several years in tidal jetty.


I have noticed that 4 of the aft keel bolts, extending from the inside down to the underside of the keel are Stainless Steel. (approx 500mm x 15mm dia.) Is this a potential galvanic corrosion problem?

What, if anything should be done?

Also some stainless steel stiffening has been fitted in the bilge between a floor and the centreboard casing. Is this a problem?


Many Thanks.

 

[Peterduck]

Stainless steel will definitely be a problem, especially if the rest of the hull [e.g. planking] is fastened with copper rivets or bronze screws. As a rule of thumb, do not use stainless below the waterline. If your boat is copper fastened, replace the keel bolts with copper rod, threaded at each end. I would advocate removing the stainless strengthening piece from the floors, and replace with bronze or copper strap. Try to keep all metal work as compatible as possible. Stainless steel does not like to be buried in timber where it cannot get access to the oxygen which in other places prevents it from corroding. In anaerobic conditions it will waste away quickly [called "crevice corrosion"]
Peter.

 

[ccscott49]

I agree about the stainless, but would use bronze keel bolts/threaded rod, (available from classic marine) I feel copper is two soft and then work hardens and becomes brittle. I would also use bronze for the floors. IMHO of course.

 

[AJAWATER]

This has got me a little worried! It looks like a very dificult job to remove these bolts. Just how serious is the problem? I can live with some corrosion of the stailess bolts as it will make them easier to remove once they start causing problems, but would be very worried about degrading the copper and bronze fastenings in the rest of the hull.

Is there any form of cathodic protection, or anything else that i could do?

Thanks.

 

[ccscott49]

You shouldn't degrade the copper or the bronze fittings, but you will degrade the stainless keel bolts, you may also get some wood degradation. IMHO, FWIW

 

[Mirelle]

In a word, yes

It most certainly will be a problem. You do not say what the ballast keel is made of or if these bolts go through it - if it is cast iron, and they do, then replace them with either wrought iron (which is ideal, you can get it from the Real Wrought Iron Company whose website is a mine of information, or mild steel. If the ballast keel is lead, use bronze.

Get rid of the s/s strapping in way of the centreplate case and replace it with either bronze or galvanised mild steel.

Crevice corrosion at the point where oxygen cannot get to the stainless is the worry, plus all sorts of weird galvanic effects as it decides to be eithe passive or active....