finbox confusion

I’ve just completed my first board (shaping, glassing and hotcoat). I have to install a fins unlimted 10.5" channel finbox but the tail of the board is very thin. I’ve asked this question before and the replies I got said the box would be 1" deep (which I think would be ok) but the box I got is 1.25" deep. It has the fin slot which is 1/4" below the perimeter lip. My question is how much of this perimter lip can I leave above the glass and grind down once the resin has set. If I have to install the box the full 1.25" into the board I will be F&##%D. Not a good ending to a so far fun project.

Thanks in advance for all you help here at swaylocks


the 10.5" F/U box is 1" deep. it comes with a lip on top of it (i’m guessing it’s about 1/4" high) that gets removed. there’s also a little piece of plastic going over the fin plate slot that you’ll need to pop out. anyhow, the top should be sanded flush with that…and that should only make the box 1" deep.

If you have one inch thickness then you are good. The lip gets ground off. You could even go a little past that onto the actual box and take off several milimeters if you need to. The tail is rockered and taking down the back end of the box flush to the bottom of the board is’nt going to hurt at all.


 Howzit breid, Actually I think if you measure from the bottom of the fin box tab to the bottom of the box it's only 7/8". What I do is shim up the rear end of my jig and as I rout the area I check the depth so not to go through the deck. Most surfers don't have the fin at the very end of the box and even if you do all that happens is the fin tab ( if at the back of fin) will stick up a little above the box. Use some calipers to determine the thickness of the area where the back end of the box goes. Aloha,Kokua

Kokua’s right, it’s only 7/8" to the part of the lip that touches the glass. I route my first pass at 1/2" deep, then 3/4, then 13/16 (1/16 less than 7/8). I then adjust the depth at 1/32 increments until the back of the box is down. Templates will bend some when clamped depending on tail rocker, so I always start checking the depth using the box at 3/4". Don’t forget to clamp the box in when you set it so it doesn’t float any further up.