Mast Step Reconstruction

[big_s]

Hi all,

I have a Samphire 26 yacht.

On investigating some rot under one of the cable glands in front of the mast step I discovered that there was rot extending under the mast step.

The main body of the mast step is an fibreglass encapsulated hard wood block built in top of the deck. The deck is a (balsa?) cored construction. The area directly under the mast step is marine ply covered with a solid layer of fibreglass to deck level.

The cable glands have led to some deck core rot and the mast step plate through bolts have led to water ingress and moistening, but not rotting, of the marine ply.

After taking height and dimension references, I removed the mast step, underlying fibreglass layer and marine ply. This area now exposes the layer of fibreglass forming part of the saloon ceiling.

My question is how best to reconstruct the mast step to the original height and shape? Should I replicate the original construction method or would it be better to use a single thicker hard wood block and eliminate the marine ply layer?

Any thoughts on associated layup using poly resin and/or epoxy, expoy high density fillers and cloth weights/types would also be much appreciated.

Many thanks.

P.S. Pics to follow...

 

[William_H]

The deck rebuild will be fairly simple. Being at the base of the mast no concern re replicating non skid surface. Smooth will be fine. I did a similar mast step block reconstruction in my case an aluminium wedge that corroded. Deck itself was solid. I simply built up a block of GRP from the thickest chop strand mat I could find and polyester resin. Just have to be patient and wait for it to go hard then sand back to decent finish. You can put pigment in the last coats of resin or paint.
Yes you could fit a hard wood or ply block but solid GRP is for ever. If you are in UK or further north cold temperature will make GRP work a bit more difficult but at least with polyester you just add more hardener. You don't need epoxy as all load will be in compression.no chance of loss of adhesion. ol'will

 

[big_s]

The deck rebuild will be fairly simple. Being at the base of the mast no concern re replicating non skid surface. Smooth will be fine. I did a similar mast step block reconstruction in my case an aluminium wedge that corroded. Deck itself was solid. I simply built up a block of GRP from the thickest chop strand mat I could find and polyester resin. Just have to be patient and wait for it to go hard then sand back to decent finish. You can put pigment in the last coats of resin or paint.
Yes you could fit a hard wood or ply block but solid GRP is for ever. If you are in UK or further north cold temperature will make GRP work a bit more difficult but at least with polyester you just add more hardener. You don't need epoxy as all load will be in compression.no chance of loss of adhesion. ol'will

Thanks Will. I hadn't thought of going the solid grp block route although the amount of layers to create a 3 inch thick block is daunting. It does solve several issues and simplify the build though.

 

[justanothersailboat]

I had a similar problem - rotted out ply in the mast step caused by badly sealed cable sockets, the metal casting "socket" that the mast foot slots into was bent like a banana...

I dug it all out to a clean surface and then build up the whole block with epoxy and woven glass. Not having made such a big lump before, I paid rather patient attention to heat, wetting, and bubbles. I did it at the very lowest end of the epoxy's temperature range - I think if I had done it on a hot day it would have cooked! Then flowcoat over the top to make it look right and protect the epoxy from UV. The result seems rather solid and I am pretty happy with it, but my epoxy-glass brick is only about one and a quarter inches thick. I think it would be expensive and timeconsuming to do this right to a three inch thickness. I have never dealt with your situation but I think if I were in your position I would consider epoxy glass in place of the ply, then a hardwood block, then more epoxy glass - as a sort of "sandwich". I'd heatgun epoxy into the surface of the wood so that it was well sealed, like you do to the edges of ply to make it last longer, and also in the hope of getting a really great bond to it. And route the cables outside the block, even if that meant replacing a small patch of balsa core with epoxy.

Samphire 26 looks rather nice to me... good luck!

 

[big_s]

I had a similar problem - rotted out ply in the mast step caused by badly sealed cable sockets, the metal casting "socket" that the mast foot slots into was bent like a banana...

I dug it all out to a clean surface and then build up the whole block with epoxy and woven glass. Not having made such a big lump before, I paid rather patient attention to heat, wetting, and bubbles. I did it at the very lowest end of the epoxy's temperature range - I think if I had done it on a hot day it would have cooked! Then flowcoat over the top to make it look right and protect the epoxy from UV. The result seems rather solid and I am pretty happy with it, but my epoxy-glass brick is only about one and a quarter inches thick. I think it would be expensive and timeconsuming to do this right to a three inch thickness. I have never dealt with your situation but I think if I were in your position I would consider epoxy glass in place of the ply, then a hardwood block, then more epoxy glass - as a sort of "sandwich". I'd heatgun epoxy into the surface of the wood so that it was well sealed, like you do to the edges of ply to make it last longer, and also in the hope of getting a really great bond to it. And route the cables outside the block, even if that meant replacing a small patch of balsa core with epoxy.

Samphire 26 looks rather nice to me... good luck!

Thanks for your thoughts and the tips. I like the idea of an all glass block but, as you suggest, I am coming round to the idea of a hardwood block filler just to reduce the percentage of the step built from resin/glass.

I think my solution will be several layers of heavy csm and epoxy to bind to the open ceiling surface, a dam of high density epoxy filler around this to just below deck height, a hard wood block bedded in epoxy, heavy biaxial/csm cloth mix layup, finishing cloth and finally flowcoat.

 

[justanothersailboat]

Today I learned there's a special kind of chopped strand mat you can use with epoxy! Didn't know that.

I used a bit of biax but I used plain weave for most of it. It may not have been optimal but it seems to have been ok. I happened to have some woven glass tape the exact width of the mast step which simplified cutting it up quite a bit.

Your plan sounds good to me.

 

[William_H]

I would reiterate use polyester resin cheaper and more suitable for lower temperatures and ok with CSM. ol'will