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Y25-II chainplate leak/bulkhead repair


Mar 30, 2018
Yamaha 25mkII Ballard
i'd had a suspicion i had a leak this winter, and i finally caught my chainplates actively leaking after a recent heavy rainstorm. there is a little bit of rot visible right at the bottom of the deck around one of them. i'm going to have to fix this at the next haulout, so now is the time to figure out how to proceed.

i've read up a bit, and right now this is going to be my plan of attack:

- get the old chainplates out & construct new ones from them as patterns.

- do some exploratory surgery on the bulkhead to see how far the rot runs. at the surface rot does not appear to have extended much past the immediate point of leaking but I expect it to be worse than it appears once the chainplates are off.

depending on severity i will either:

a) replace the entire plywood panel. this looks straightforward enough, but involves a fair bit of furniture disassembly in the cabin.


b) if the rot is limited to a small area, cutting away ply-by-ply in a "inverse birthday cake" manner to clean wood from either side & treating with boric acid anti-rot. then glue new plies in, allowing significant lap joint overlap with each additional layer. i.e. the innermost ply is the smallest piece and each layer of ply is 1-2" larger then the one underneath it. depending on extent i'll probably lengthen the chainplate a bolt or two into virgin bulkhead.

- reinstall, using butyl tape as sealant around the deck penetrations.

does this sound about right? any words of advice? anyone had to do this repair on their yamaha 25?
Nov 21, 2012
Yamaha 33 Port Ludlow, WA
Pictures always help! Others may have had similar issues but are not familiar with the Yammies. I have a Y33 and had to replace the chain plates due to crevice corrosion. There's a thread with pictures in this forum. I pulled the chainplates and had new ones fabricated and polished. The rigger (Brion Toss) recommended increasing the amount of material above the top attachment point because the originals had slightly elongated holes. This change was incorporated into the new plates.

I also had a minor amount of rot around one chainplate. I drilled a grid of holes in the top skin around the chainplate and filled grid and deck penetration with Git Rot. This had the added benefit of creating a solid epoxy core for the chainplate deck penetration. I redrilled the holes and finished with a rasp. I filled and drilled the other penetrations as well. 3M 4200 was recommended by the rigging crew for sealing the plates. It failed within months. I dug it out and used butyl tape. That has worked pretty well, but I still get a drop or two if I've been sailing hard. With the deck core now protected by epoxy I don't worry about it as much.

I don't have pictures as I found the rot just before we were scheduled to restep the mast and it was pretty much an all-nighter.