72board.com
25 modification - building deep foil box
May 10, 2022
Materials
6oz Carbon Fiber Cloth
4oz Fiberglass Cloth
Epoxy Resin
Glass Microspheres Filler Additive
Epoxy Glue
PVC Foam
Tools
Deep Foil Plug (the mold)
Packing tape
Mold release wax (Partall#2) and PVA liquid (Partall #10)
Vacuum Pump, Bag, Hose etc.
Dremmel, Sandpaper
Clamps
Steps
Create the plug
Create a plug from wood - exact same dimensions as the mast head.
Make the "cups" and posts for the fin bolts.
Cover plug with packing tape (smooth surface acts as a release) and Partall.
Create the foil box
Laminate the cups with carbon fiber.
Laminate the foil box. I used 12-14 layers of carbon fiber.
Put in vacuum bag to cure. (Use Peel Ply, Perforated film, Breather Cloth, Vacuum Bag).
Remove the vacuum bagging materials.
Separate foil box from plug (screw in bolts to pull the mast head plug out of the carbon fiber).
Trim the carbon fiber edges with a dremmel.
Attach the fin bolt "cups" to the foil box with epoxy glue.
Cut PVC foam to fit the box.
Assemble the box using carbon fiber, epoxy resin and resin thinckened with glass microspheres.
Clamp box until cured. (Use tape/plastic to prevent clamps from sticking).
Remove box from clamps, sand edges flat/square.
Check fit on the mast head, sand the slot if necessary.
Notes
The bolt pattern for a tuttle vs foil mast may be different. So a slot rather than hole may be necessary to accommodate different fins/foils. Also, creating a deep "cup" for the bolts puts the bolt heads nearer the top of the mast head and therefore requires smaller bolt slot than if the bolt heads were at on the deck surface.
When creating the cups, an initial layer of 4oz cloth makes it easier to wrap the carbon fiber around.
I used gorilla glue to stick the larger bottom pieces of PVC foam together before finally assembling the box with carbon fiber and epoxy..
There are some good videos showing similar techniques for building a foil box:
https://www.youtube.com/watch?v=rpfZXUwUSpY