Compromises - Ballast keel?

hi all!

I am renovating a sail yacht from 1908 and it has an iron ballast keel. The keel is around 1.5tons and has 7 iron bolts size M26. The yacht is built with steam bent oak frames and fastened with copper rivets. The keel bolts are very rusted and I was going to start by removing the keel and getting it sand blasted and coated with primer and then some suitable paint.

Now, I need to choose the mateiral for the bolts. The most compatible bolts are of course galvanised iron bolts. But, I read in some books that it is best to replace them with stainless steel bolts. But, i also read that stainless steel should not be used below waterline, especially if the keel is oak.

So, what is a good solution!?!

1. replace the keel bolts with galvanised iron bolts
2. replace the keel bolts with stainless steel bolts.
3. redesign & cast a keel in lead and then use stainless steel bolts.

I see that this is an exercise in compromises.

So, if I say that I want to make the best possbile choise, in terms of longevity of the keel bolts and the boat. what would be a good solution.

The cost of this choice is small compared to the entire project. I would like to rebuilt the boat like it was before with copper rivets for fastening the planking to the steamed oak frames.

What would be a good way to go?

Please let me know if I missed any details. Thanks for any tips.

Mohan

 

Well, given that the original setup lasted about a century, how many centuries are you planning to use the boat? Now, before you get your panties in a twist, I'm just being a bit facetious, but with an edge of seriousness. As long as the bolts are completely isolated from sea-water, (with epoxy or polyurethane sealer or good old axle-grease for example) they won't corrode. Oak does have acidic tannins in it, and it will attack metals if left in contact with them for a while, drilling the hole oversize and filling the space with something inert might be a good idea.

Yokebutt.

 

Stainless Steel bolts and nuts are not a good idea for any thing that has stress. SS threads have a nasty feature that is only theirs. The threads " cold weld " together. That means when you start to unscrew them they get tighter and tighter till you have to snap or grind them off. If you can do that without ruining nearby stuff. SS does not like complete and continious submersion, depending on the type and the liquid concentrations.---------------Use the iron, steel, plastic, wood, anything but SS.--------------------------------Web search -- stainless steel corrosion-- Read the Mcnally Institute site about ION corrosion. No salt water.

 

I believe you have two choices. 1). Replace the bolts with the original type. This is a reasonable choice, is the least expensive, and they will last a long time. 2). Recast the keel in lead and use Silicon Bronze bolts. This is the best choice, but the ballast needs to be redesigned due to the difference in weight. Never use Stainless Steel below the waterline.

 

Your choices are limited by the ballast casting, the keel material and the environment. Stainless doesn't survive long in oak or salt water. I don't care what you put on them or try to surround them with, the tannins in the wood or the salt water living conditions will eat them up pretty quickly. This is why galvanized steel or iron bolts were used and are recommended on iron castings.

Re-casting in lead isn't a good idea either. The cost alone should be enough to fend you off the idea, but the vessel can have major issues with the lowered CG. Yes, the boat could benefit from the increase in the righting arm, but it will also increase the loads on the rig and it's attachments to the hull and mast(s) This change can be performed, but may require you substantially upgrade rigging parts, assuming the whole rig, sticks and all, don't have to be sized up, which is quite possible. This type of change should be worked out by a designer, who can draw up a new casting and figure the new loading on the hull and rig, for their needed modifications.

 

Thank you for your comments.

After reading your replies, I have decided to go the way of just replacing the bolts with galvanised iron bolts. I will unmount the keel, get it sand blasted, and then paint with primer and then a paint. Replace current iron bolts with galvanized iron bolts. That way the keel should atleast last a "little while" if I do it carefully enough.

I appreciate your help very much. Cheers.

 

What's another couple of centuries between friends, anyway?

Wish I could go sailing with you,
Yokebutt.

 

i know this is very late but i might not be toolate to make a sugestion.

has the periodic table of elements been reduced to iron or something?!?!?

you could get the bolts in a metal such as phosphor bronze or you could get mild steel bolts and get them chemically blacked so that they are seawater resistant?