Rot in the beam shelf!

[joliette]

Having just got the old girl spruced up and looking good, I've discovered some rot in the beam shelf! This has been caused by rain water entering via a poorly sealed deck fitting that has been fastened directly through the beam shelf with two bolts. Some exploratory surgery has revealed that the rot has spread over a distance of about three feet and has also effected one or two ribs and deck beams!

I'll need to get enough deck up to give access to laminate in about five foot of beam shelf, to replace the ribs and deck beams. The original beam shelf, ribs and deck beams are in elm.

Advice from anyone with experience of doing such a job would be appreciated. In particular, advice on materials and scarf joints (when laminating in situ?).

 

[tillergirl]

Not sure about providing advice but can relay my experience. TG had some serious rot in the starboard beam shelf caused by long term failure of the deck caulking - in turn I think caused by failure of the teak deck fastenings (steel screws). In the end I replaced a 25ft length if I remember correctly (I can look out the pictures). Cut two scarfs 10:1, one at either end. Only difficulty cutting the first scarf was that as I cut, the joint naturally wanted to close on the saw. But it was possible. The replacement was two planks scarfed together which we did first and then bent and trained to shape on a jig made out of the old covering board: we left it there about two months well clamped up. Although it straightened back on release, it was clear it had got the idea as it bent into position quite easily. We tried it dry first before removing and then applying glue and finally inserting and copper riveting the scarf. I have to say I was quite proud of the results.

I also had it affecting the half beams and the top of some ribs. The gunwales had also largely gone and were replaced. It was a straight replacement of the half beams and I sistered the oak ribs. I did consider a laminated repair to the ribs but it was a task too far. Overall I was lucky as most of the damage to the ribs was only an inch or so. I guess purists might point out that I failed TG in sistering the ribs but it certainly hasn't caused any problems. I guess the key things were:

Access - and I was replacing all the deck so everything was stripped away although I did compromise over internal fitting removal and kept this to a minimum;
Good tools - I treated myself to a new saw for the cutting of the scarfs; compaired to the cost of the timber, it was a minimal expense and I found something that really suited me;
Clamps - stacks and stacks of good sized ones;
And the usual rules about thinking and measuring twice - oh and a beveled edge to help the bend. I guess depending where this repair is, the length of the repair might be guided by the need to get clear cuts for the scarfs and to maintain sufficient strength in the beam shelf. My starboard beam shelf is now effectively four 8 ft lengths (not counting the scarf overlaps). I don't think I would want a repair to be too short but I confess that is based upon a feeling that too short a repair might be weak not knowledge. My mechanical knowledge doesn't extend that far.

Looking at the pictures, all of the half beams were removed before replacement but I had three bulkheads still in position that were useful for getting the new beam shelf into position.

I can try to scan the photos if you want me to pm them although they don't really add a lot to the above.

But its very do-able. Good luck

 

[ccscott49]

Do you need to scarf? Why not just overlap joints, glued and screwed with bronze screws, laminating three or more layers. Easier to bend to shape and just as strong, agree with the sistering, easiest way.deck beams can also be layered (laminated).

 

[tillergirl]

Don't know if I needed to scarf but I did! And I'm not sure now why I chose to copper rivet rather than using bronze screws - I think I had the copper nails and roves to hand.

 

[ccscott49]

I was thinking bronze screws, only if you were going to laminate, to pull the layers together to allow the glue to set. Copper rivets I'm sure are fine if its one piece. Didnt mean to pull your tail!! Answer was directed at Joliette, trying to be helpful, sorry.

 

[tillergirl]

No offence taken. I was trying to remember why I did certain things - it was 1996! I seem to remember that clenching up the copper nails was rather satisfying - for some odd reason!

 

[joliette]

Thanks for the excellent advice. I've now lifted the cover board and managed to cut out the decayed section without raising anymore of the deck. I've cut out a 1 metre section and think I'll just about have enough room to laminate in a new section. I've cut lap joints in the beam shelf. I'm thinking of reinforcing these joints with butt blocks either side of the beam shelf and pulling everything together by passing long bolts (made out of st.stl rod) right through top plank and new beam shelf. Ought to be better than new?

 

[ccscott49]

Use Si bronze instead of Stainless, you can get it from classic marine, or anglia stainless steel. No chance of crevice corrosion, stainless rusts when deprived of oxygen, bronze is only marginally more expensive, good luck!