In an ideal world you could probably get away with just a wee bit of glue …
**Reasoning? **
Think about how the box translates the forces on the fin (Above, Honolulu and others make the point.) There’s very little trying to pull it out of the board except a small component of the drag and gravity… and maybe a curious nephew. This of course assumes that your setup isn’t some highly toed creature or you’re not doing something equally creative(?), say, using some curious gizmo like a turbo or a swivel fin or a wingy thing, in which all bets are off… and you should opt for the full treatment -i.e. cement the sucker in. (By the way, in my opinion, most of the time, virtually all such gizmos just manage to generate whole new realms of undesirable drag, as opposed to desirable drag which is what most of surfboard design is about.)
The engineers will tell you, the typical forces on the fin result in a lot of moments, all of which must ultimately be handed by the box walls (the forces resolving somewhat differently for glass-ons)… the connection between the top of box really isn’t a big player (in translating those moments and forces from box to board) so just a minimum of glue or glass over is likely to be enough in an ideal world.
So if your box is deep enough you’ll probably be fine… assuming the best of all worlds… but then who does that…
Ah, but then there are the cosmetic arguments, ‘it just looks good or professional’, or even the quasi-hydrodynamical argument (like exposed boxes cause excess drag or something like that…), and I’m sure there’s also a quality control argument too, (which escapes me at the moment.) But such musings are beyond me… anyway, who, knows, right?! Surfer’s are always thinking outside the box…(ouch.)
kc
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