So I got a single fin and am seeing suspect play in the fin-box assembly, anyway to fix this short of speaking with the builder?
Get it professionally reinforced with fiberglass cloth on both sides and above and below. Otherwise you'll end up with a constantly worsening wobbly fin box rot situation. It turns ugly and your whole tail becomes waterlogged and the foam gets soft underneath the glass and then you get delamination and contamination and the board goes so slow it feels like constipation.
Dang thats a pain, i was thinking a slow cure 2-1 marine epoxy may work in there nicely for sealing and structural strength once its set down in there.
If it is as new as it looks in the picture, and if the builder is nearby, have builder do it. He probably has more experience than you do having done lots of them. just opinion.
If it was mine and the builder wont fix it, id cut the box out and reset it ,to pile cloth on top of it might not last and looks terrible,one thing tail is under water more so pressure will force water in so fix it soon cuz next it will rot your stringer
Looks like the box wasn't prepped properly, or the glasser who installed the box used sanding resin instead of laminating resin - the bond that's failed is between the box and the resin in the routed hole. This probably means there's not much water getting into the foam, but there's always a chance that it is... you gotta fix it, and not with marine epoxy. My recommendation is to pop that box out and route out the resin using the proper jig, then do a clean install. And if you can't pop the box out, rout out both the old box and the resin. And by the way... this is a good argument for the fin box patch to go OVER the box instead of under, and for the use of a cloth "sock" around the box. If either one of those box install methods where used here (I do both), you'd never have had this problem.
Looks to me like the sander might have overheated the box when he ground it down flush with the bottom of the board......I've made that mistake myself. When you're grinding boxes if you create too much heat the plastic expands and then when it contracts you lose the bond to the fiberglass.
