I'm sure there's a sailor out there who's had a similar problem:
This winter I very carefully repaired a P18 hull (left side) that was split from the top of the transom to 4 or 5 feet up the inside seem.
I bought a couple dozen pinch clamps and rounded up about 10 C-clamps, injected WM goop with a big caulk gun and clamped the sh1t out of that seam. 24 hours later, I tipped the hull up and poured some of the goop down the seam. I got lucky and had it at just the right consistency so it ran down the seam from the inside like syrup and left a serious coating on the inside of the joint. I did it to make sure the bond would be totally waterproof, but I'm sure it had to add a certain amount of strength. No way was that split gonna open up again!
The trouble is it did...after about 3 hours of pretty rough seas on the first sea trial, I heard an ugly crackle sound. The crack is back!
I'm not sure if it sepparated at the same place...in fact I think it is different layers of the hull laminate. Untill I got a good look at it my first thought was to through-bolt it with a bunch of small ss screws, but in parts of the split the inside half is very thin. This also leads me to believe that it DID NOT split between the deck and hull joint, but the fiberglass itself is weak.
The top of the transom is still solid, so at least I got some strength there, but what if I simply bond this new split back together only to have the 'glass come apart in a new area? I would have bet a lot of money my repair would fix the problem forever, but now I'm not sure if I can find a way to ever trust my repair for deep-water sailing.
Thanks for any help you guys can offer...my family says they will not sail with me untill they know the boat is solid.