Sister frames

[roh]

I've just bought a new boat (1937, teak on oak) and have found that a number of the frames are cracked so I want to strenghten with sister frames, however I am unsure of the best approach.

Do I :

1/ Steam bend (hard to do as I don't have a steam vessel) similar size frames and copper nail / screw to originals
2/ Laminate thiner strips in situ next to originals and epoxy / glue in place
3/ Cut from board the profile, then glue and screw / copper nail to original

Any thoughts about the best approach would be welcome.

Thanks

Regards

Richard

 

[Strathglass]

I have replaced floors by steaming thin strips clamped in position. Epoxying the together when set and clamping them in place with pvc between them and the hull. Removing them when set, clean them up and screw them back in position.

Steaming is easy just get a low cost wallpaper stripper and feed the output from it into the end of a plastic drain pipe. Put the wood inside and block the other end with a rag then keep the stripper full with water and switch it on. You may have to insulate the pipe but otherwise that's it.

Iain

 

[jleaworthy]

The problem with sister frames is that you stiffen the hull above and below the fracture of the cracked frame. This will intensify the stress on the sister frame where it lies alongside the crack of the original timber (obviously a high stress area anyway- that's why the original cracked) making cracking of the sister frame very likely. Better to remove the cracked frame completely and replace with one possibly of increased scantlings.

 

[Mirelle]

I agree - it's what I have done over the years. Fasten through the same holes in the planking, and if you cannot get to the ends of the old frame, scarph it. Really, you need to find out what caused the old frame to crack - it might be accident damage or it might not. If two or three frames together have gone at the same spot, consider raking out the caulking in way before re-framing, so as to get the hull fair again.

 

[Johnjo]

All the ribs/ frames I have ever repaired, always removed the broken
ones, usually find that the planking has formed a small angle on the
break, which is difficult to correct with the old in place and usually
ends up cracking the new, this can lead to the cracking of the remaining
ribs/frames along the seam of the planks concerned, and I think looks
a lot better job at the end,
All the best with it
mike

 

[Aussie]

Just been through this same process with my fathers boat, we added sister ribs alongside the original ribs and frames using laminated timber but not glued together. it produced a good result but it introduces extra holes in the planking.
In hindsight it would have been easier to remove the old ribs and frames and steam bend new ones in place as the garboard strakes had to come out and be replaced anyway, many of the old ribs were'nt broken but the ends had popped out of the rabbet in the keel, another thing we noticed was that the original rib timber was absolutely soaked with deisel, does anyone know if this causes the timber to deteriorate?
Cheers Aussie