I didn’t think too much and ended up not installing a stringer on my EPS-epoxy soon-to-become singlefin. How do I install the US-Box so it’ll be strong enough? Do I make the hole deep enough to hit the deck?
Sorta depends on the EPS density and glassing schedule.
20kg/m3 and higher you can use microsphere thickened resin to set the box. I lay some glass all along the cavity prior to pouring the the resin in and I also make sure that the edge immediatly under the glass is scoured away with a nail or some other shap instrument. The idea is to maximise the bond with the skin. You pour the resin, set the box, tape it all up and when hard you sand the box down level. It is good practice imho to cap the box with a large football patch and re-hotcoat. This will give you maximum bond with the skin, the glass reinforcements in the cavity should hold off any weakening of the eps around the box and resin seeps into the eps immediatly around the box making that more water resistant in case your box breaks/cracks in a collision. Some boards are thin and you do actually end up bonding the deck skin as well but YMMV.
For lower densities I would suggest a hard foam insert. With windsurfers I have done it using expanding PU foam to make the insert and had some good results. Basically you rout a oversize cavity, squirt in the foam and clamp a flat piece of plastic or plywood covered in cellophane over the cavity. Make sure there is a hole in the clamped piece to allow excess foam to escape. When hard, use a rasp or sander to flatten to the board shape and proceed with box install as per above into the PU. Of course you could pre-fab the insert or use other hard foams. Imagination…
Thanks, dave! I have one question though: what’s a football patch? is it a patch that is shaped like a football? and it covers the whole box area after sanding the box down? Meaning the surface of the box in level with the bottom is covered with the lam. Do you then cut out the cloth that’s covering the fin slot?
yeah a patch that covers an area larger than the box, tape the slot before so no resin seeps into the box. the patch adds some strength to the bottom skin and seals the box to the skin. you then hotcoat the the area again and do the final sanding to even the whole thing out again.