another fin box question

Aloha

I am trying to get a 7" center fin into a F/U box, and when the fin sits in the box, the base of the fin is raised above the bottom of the board by about 3/8" of an inch or so, rather than sitting flush in the box.

I tried a different fin in there, and it also sits above the bottom of the board. It appears that the box was set in at a slight rise and then sanded down, but the groove where the fin goes is raised at an angle as a result.

Should I grind down the base of said fin at the leading edge to encourage the fin to sit flush in the box, thereby “correctifying” the situation? Help, help, swell is on its way!!

Aloha

Kit

You can safely ground off the base edge of the fin IF you have enough room to do so below the cross-pin. If not, you will break the cross pin out in the surf. With 3/8", I am wondering if you are screwed and need to get a new finbox and re-route the hole to the appropriate depth.

3/8" is a LOT to miss by. Most people do not realize the box is going to rise about 1/4" when the resin sets, and depending on how hot you run that batch and whether you clamp the box down, it can be even more.

Tricky business - that gluing boxes into blanks stuff…

thanks for your reply, Blakestah. I just measured the rise and it is 1/4" inch, instead of 3/8". The good news is that the cross pin is at the other end of the fin, so I should be able to sand safely.

If I leave it “as-is,” will this affect performance (i.e. having a slightly raised fin)? I am not concerned about water flow at the base but the angle of the fin. This is for a 5 fin bonzer too, so more variables in the mix.

Quite honestly, I’d take it back to the shaper and demand he fix it before riding it. It oughta be free, the glasser screwed it up. The finboxes are built with extra lip to allow it to be ground down.

I can’t really visualize how the angle is changing from here, but a 5 degree change in rake angle will be quite noticeable. Before sanding the fin, I’d talk to the shaper. If you’re good you should be able to get a loaner and get them to install the finbox properly. There should be 1 inch of depth in there.