Hi…I’ve seen a bunch of different methods for dropping in a single fin box into 1.5# styro. I’m making a big 10-6 glider that’s gonna house a good size 11" fin.
Wanted to get your opinions on what method is the most nuke proof. The board is not vacum bag composite sandwich…I just hand laminated 6/4 on the bottom and 6/4/4/ on the deck.
Waiting to hear from y’all before I drop a box in. Appreciate any of your input.
I usually use an HD foam insert that is foaming PU glued into the EPS blank.
Install is capped with glass and resin.
No bagging but a small nod to the windsurf industry.
EDIT: added pic of finished box with a Robin Mair fin. I probably should have painted the HD foam with white epoxy to make it blend in more and/or not yellow but sometimes I just let things be what they are- some HD foam given to me by my fiberglass vendor here in Minnesota.
Another option is a balsa insert.
Very well done. I’d give 10 points, if it was allowed.
Thank you everyone…I do have some divinycell as well as corecell and will get on it…
Would the balsa method be strength sufficient as the pvc foam?
My main concern with balsa is keeping it sealed so it doesn;t take up water.
There are other ways to build in robustness to a fin box install.
Looking for the Bruce Jones mini-stringers picture I saw this old thread:
https://www.swaylocks.com/forum/59943/q-bout-replacing-fin-box
Easiest and strongest way is to just use this stuff https://www.aeromarineproducts.com/product/4lb-density-foam-1-2-gallon/ . Never had a box come out in 10 years of repairing eps core boards. Cut the slot about 1/4" larger all around and you’ll need to clamp the box down and use a piece of plywood for vertical alignment. Trim the excess then put a glass patch over. You can also pigment that stuff. Keep what’s left for repairs. It’s best to do this post-glass since you’ll be clamping the box down with wood strips out to the rails (front & back).
For inserts of equal dimensions, balsa would likely be stronger (8-14 pcf) than HD foam – related to density, pounds per cubic foot, pcf.
As jrandy mentioned, balsa will soak up water if the glassing around it cracks. But if the HD foam is not closed cell, it will soak up water too. Difference being, balsa will rot if it soaks up water, while HD foams “may” not.
If installed before glassing the board, an insert that extends from deck to bottom surface will be much stronger (glass skins on top and bottom). But that requires much more accuracy and precision in shaping. And you don’t want to cut entirely through the stringer to install it. Curved ends on the inserts will minimize the potential for “hinging.”
If it has a stringer nothing special but cut accurately so no gap low resin content no exotherm fusing eps. Use cabosil and or flock in the mix, cap over with glass, easier and effective to do with those new US box plugs with flange (future…). If no stringer, add one, the length of the plug, through the board 3 to 5 mm marine ply. Alternative is to drill 2 to 3 20mm holes in plug cut through the blank, glue in wood Pilar. Connected plug with deck with something hard is the best way to go for me since I spend lot of time those last 2 years to repair foil boxes…
