Should the 10 1/2" Fins Unlimited fin box be installed before or after the hot coat and with what grade of sandpaper or grinder be used to remove the lip that sticks up around the perimeter of the fin box? Also, what brands of fins will the Fins Unlimited box accomodate? Thank you Ambrose for the previous response, it was concise and to the point.
Both are possible. If you choose to install the box before hot-coating, just be sure to protect the whole bottom of the board from the dust that you will necessarily produce when using the router. Grinding the top of the fin-box can be done with a surform or 50 grt with a sander (care must be taken not to overheat there, lower the rpms and don’t stay in the same place too long).
Sureform the tab stick out… then sand with 80.
All American box fins fit, up to 9", then you gotta sandwich the box with woodies for bigger fins, or post thru to deck of board, with deck reinforced with another 3 layers of cloth.
Euro fins will need sanding at the base to fit.
I saw off the lip to about 1/16 above the bottom then sand the rest with 80 since you’re going to lam a patch over it anyhow. I think that sawing is safer than a 50 or 60 grit disk which can take a big bite out of the glass if you slip. I use a Japanese woodworking saw (Harbor Freight) and mask around the box with 3" tape.