Steel frames, galvanised or stainless?

[steve jones]

I came across a potential project recently. I expect that it's too big a stretch for me but can't help being drawn towards it.

The boat is a fairly substantial yacht, built in the 40's using the Scandinavian style of mahogany planking on steel frames. In fact it's a mix of steel frames and steamed oak, one steel frame then two timber... The steel frames are from angle, around 30 x 30 x 3mm, rolled to the hull shape, double dip galvanised with planking riveted on.

All of the steel frames need to be replaced. I've got "The Big Book of Wooden Boat Restoration" by Thomas Larsen, a Swede. He describes the process of making replacement steel frames which sounds laborious but doable. His recommendation is to use A4 316 stainless angle and fastenings.

I'm thinking, this is all very well in the Baltic because it isn't as salty as the seas around the UK. I know lots of people are dead against using stainless fixings etc... below the water line. But a restoration using galvanised frames would be difficult because they would be replaced one at a time, rolled, drilled and fastened. Stainless could, to some extent be done in situ whereas galvanised frames would need to be formed, have all the holes drilled and then be taken out again to be dipped.

Does anyone have any experience either of working on a boat like this or sailing this kind of vessel in regular salty water (with replacement stainless frames) for any length of time?

Thanks

ps. I fully appreciate that taking on big restoration projects is stupid and I shouldn't touch this with a galvanised barge pole.

 

[Wansworth]

What does your wife think?

 

[Motor_Sailor]

Well, as you have intimated, you need to have a material that allows you to make an effective repair in all the parts, ie the fabrication, the fasteners, etc.

Spirit Yachts have used stainless frames in a strip planked hull on many occasions, so the saltiness isn't an issue. Your only really consideration is whether the bolts in the planks are through dry, epoxy coated, encapsulated wood or through relatively more damp, traditional style planking protected by a conventional paint system. Stainless doesn't like being damp with 'stagnant' water such as where a bolt passes through a plank, or between damp wood and a frame.

 

[DownWest]

Think it was Constellation Yachts in USA that started building Herrashoff designs on galvanized angle frames and a girder keel, to avoid the hull hogging from rig tension. The owner had a big wood business, so that was not a prob and it was a bit of a vanity project. Nice boats though.
They bent all the frames from angle on a jig, then assembled them to the girder keel, then sent the whole lot off for galvanizing.
Edit: Think the planking was conventional, not glued strip.

 

[DownWest]

I came across a potential project recently. I expect that it's too big a stretch for me but can't help being drawn towards it.

The boat is a fairly substantial yacht, built in the 40's using the Scandinavian style of mahogany planking on steel

Thanks

ps. I fully appreciate that taking on big restoration projects is stupid and I shouldn't touch this with a galvanised barge pole.

While we would love to see you tackle this and follow the trials and tribulations.... How big is this 'substantial yacht'? It sounds like the frames might be only a fraction of the overall rebuild.
And, you would have to balance the cost of stainless against the ease of forming steel and galvanizing.
Do you have very deep pockets? Such refurbs usually need them.

 

[steve jones]

Thanks for the replies.

Wandsworth.... you've obviously met her.

Motor sailor... the planking is mahogany which as you say would be protected by paint. I think you could be right that it's the fastenings that would be the most vulnerable part of this. Trouble is, I don't think any other type os fastening could be used into a ss frame without lots of corrosion problems.

DownWest... You're quite right, the frames are a very small part of the project. Nearly everything else would need to be replaced too. I don't have enough time or money to do this but somehow I can't help wanting to do it anyway.

My concern was to figure out whether the colossal amount of work and cash would result in a boat with a structure that would be expected to last a reasonably long time and be capable of being taken pretty much anywhere.

 

[Tranona]

Salt water is not the problem for corrosion in stainless. It is dampness in conditions of lack of oxygen which can result in crevice corrosion. This is likely to happen to fastening rather than sheet material although flat frames against damp planking is potentially the right conditions.

The answer is to isolate the stainless from the wood with a good sealant, particularly the fastening holes through the planking. I have stainless keel bolts through cast iron, mild steel plate, douglas fir and oak, the bolt holes filled with polysulphide sealant when the bolts were driven. Been there since 1995 with no sign of corrosion.

The other thing to look out for is any welding that might be exposed to damp conditions as imperfect welds can be a source of crevice corrosion.

 

[RobinBirch]

What does your wife think?

I imagine that she will have made the necessary arrangements and that the men in white coats will be attending to Steve shortly.