If the fin don't fit- fitting a center fin that is too tight or too loose

The US center fin boxes that are installed on most longboards and SUP's are supposed to be a universal fit.  In real life, however, there a small variances in the width and depth of different boxes and fin sizes, so sometimes the fin won't go into the box or fit too loose.  We are often asked about this and here is what you can do if the fin does not fit well:

If the fin fits too loose, the fix is to use a shim.  This is an easy fix.  At our shop we use some packing tape and fold it on itself so no sticky tape is exposed.  You can adjust the thickness of the shim by using more folds if the fit is very loose or less if you just need a little shimming.
Put the shim under the base of the fin and push it into the finbox as you push down the fin, like in the pictures below,  you should have a tight fit with the shim, no wiggling.  If you still have some wiggle with the shim, pull it back out and add a couple more folds of tape to the shim, if it's too tight, make a thinner shim with less tape.

If the fin is too tight and won't go into the box, you can carefully sand the sides of the fin base to make it fit, this takes a little bit more time and patience.  Carefully check where the fit is tight and slowly sand the area down until it fits tightly.  Often it is the bottom of the fin that is hitting the bottom of the box.  In that case, you have to sand the bottom of the base to make it fit, not the sides.  The other option is to find a fin that fits the box without sanding.

Another tip: You can use the fin key used for the side fins to put the fin plate into the box and to line it up with the screw hole so the screw goes into the plate easily.  That's it, enjoy!

This is a playlist, so keep watching for more videos about our Blue Planet products:

Inserting the fin plate into a US center box

If the fin is loose, you can make a shim like this one using packing tape folded in on itself

Aloha, Robert Stehlik
www.blueplanetsurf.com