You need to understand that delam is not something you can see (hopefully). I'm not sure if yours has foam or not, maybe someone will comment. I have a friend with a 76 P16 thats in perfect condition. A couple a weeks ago someone sat on the hull just foward of the front beam and we all heard that noise so I'm pretty sure it had a foam core. I'm assuming from what you described that the sound was indeed that sound no one wants to hear.

FYI foam core construction means the deck-hull has
about a 3/16" layer of glass on top. That is bonded to about a 1/4" layer of foam and then another 3/16" layer of glass. A sandwich. Delam occurs when the foam seperates from either layer of glass. If you push on the hull where it was sat on you will probaly find that the area is soft compared to the rest of the deck. Don't push too hard you don't want to spread the area, or like suggested above take the handle of a screwdriver and lighty tap and listen for a change of tone. Hope this helps.

Someone a while ago posted a picture of a hobie hull cut or busted open. If I can find I'll post it so you can see what a foam core laminate looks like.

Have Fun