The board is a 10’6" noserider with a 2" High density foam stringer sandwhiched by two 3/8" baswood stringers.
I will be using a fin box, and naturally it will sit in the middle of the foam stringer thus not adjacent to any wood. There will be a glass loop on the deck for a leash.
Can I get away with just glassing it in as normal or should I add two side pieces of wood that run perpendicular to the box to contact the side stringers for additional support? And if so, anybody have any advice on that matter?
Here’s an idea… after routing your box channel, take a knife blade and cut the foam along the sides of the channel until you hit the stringers. Do this about 1/2 the depth between the board surface and the bottom of the channel. The cuts will be sideways from the inside of the channel towards the stringers and won’t be visible from the surface. This will give you a resin bridge that will anchor your box between the wood stringers. Glass a patch over the box. I’d also consider a through the box leash attachment rather than a loop but that’s just a personal preference of mine.
How about using a 2" x 12" block of balsa with rounded or V’d ends, route & install that between your stringers and router the fin box hole into that block? It would be strong and look good, and probably not add much weight by the time you made a hole big enough for the fin box…
Well, when you think about it, how much contact does a fin box have with a stringer in a ‘normal’ single-stringer board ? Especially as those boards have plain old relatively low density foam surrounding something like 95% of the fin box. And those seem to hold up pretty good. It’s not as if there was glass cloth tying it all together, generally the fin is just set in a hole with some resin and such to bed it and glue it to the foam and that’s about it.
With the high density foam the fin box would sit in, plus maybe bedding the box in some cloth to tie it into the lamination over all, I think you’ll have something stronger, not weaker. You could inlay some wood, maybe a nice basswood chunk with pointed ends, between the stringers but not all the way through, just the depth of the box, but that’d be more for appearance and psychology than anything else.
Didn’t think about the block of balsa idea. Intruiging indeed. But i think that I might take Doc;s advice and just let it ride in the foam. There isn’t going to be a leash attached to it and the surfer iot is for is quite experienced. Besides that Wlker high density foam is some tough stuff.
The sailboard industry used the “woodie” concept on a lot of boards, adding extra strips along the box. I liked this, but used 1/4" glass sheet strips along the boxes, they don’t assorb water if cracked. Glassing over the box works great, no need to tape over while glassing, use minimal resin, then route out the glass over the slot after glossing. When done,put a slight bevel along the lip of the channel, this keeps the fin from snagging the glass and pulling it loose