Our FP Maldives
had an incident with a rock before we bought it which delaminated one of the small ply sub bulkheads in the keel area from the skin. We ground it out and relaminated. The surveyor
also found that presumably the same impact had delaminated the hull
in a couple of patches up to the size of a hand palm. We ground those out with long tapers and relaminated. There was a chunk of keel missing which was replaced in the same way. One advantage of having a solid grp underwater shell.
First check out the keels and rudders for indications of damage. That should then give you a clue as to the cause.
I would suggest you have the shell in the region of the keel area (and any other areas found above) surveyed inch by inch for delamination
. The sort of impact that could crack a bulkhead like that is likely to have done other damage. The surveyors tap with a small hammer, good shell rings (doong), delaminated areas don't (duh), areas over bulkhead are very short and sharp (dong). Apologies for the poor fidelity of the sounds but if you do it yourself then practice on a good bit of hull, you will quickly pick it up. It will not work so easily in the sandwich areas above the waterline. I have surveyed 3 100 ft patrol boat decks with faulty layup
using this method and apart from being hell on the knees it is extremely accurate and easy, if somewhat tedious.
The same method will also detect if any of the other sub bulkheads, floor supports etc have delaminated which is a possibility.
The good news is that if confined to the solid layup
are relatively easy and will make the boat as good as new