Michigan Windsurfing

Windsurfing & Stand-Up Paddleboarding in Michigan

Apologies if you already saw this posted on the DAWG Facebook page....

While in Hatteras last week, Glen tried my board and rig to see if he should rig up. He came back asking what the vibration was. I hadn’t noticed, but in looking it over, we found the fin to be loose in the box (Powerbox). Turns out the screw was tight, and not too long as I tried a shorter one and it still had a little slop from side to side, not fore/aft. I always torque them down good, as I lost one on Cass a few years back for no apparent reason, and give them a fore/aft shake to make sure they are seated. I never thought to try side to side.

Today, I got that combination of board and fin out to see what I could find. Short story, I ended up having all 13 weed and straight fins, and my 3 Powerbox boards out, to see if there was some commonality resulting in looseness. Among several different fin manufacturers and 3 different board builders, it turned out almost half the fins (not one brand) were loose in all three boards. Being tapered in two views, I could not find measurements with a caliper that would tell which ones worked and which did not. After a lot of head scratching and template attempts, I observed the loose ones sat proud of the board bottom. The fin was not going fully into the board. It turned out they were bottoming out before the tapers held fast. With a stationary belt sander, I slowly took a little off the top of each fin to allow it to engage further into the receiver pocket. In some cases, the fin “base’ was now a little underflush of the board surface, some near flush. Now they all fit tight with a torqued screw.

So, I suggest checking your fins and boards. I found out one board was a touch looser that the others, so I used that one to do my tuning with. Obviously don’t take off more than needed. Even after sailing over thirty years, I still learn stuff.

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Good tip Bob.  I always fit my fins when I get a new board or new fin. 

One more tip, when the fin is loose side-to-side, you sometimes need to shim the fin.  The best solution for that I think is to use plastic shim stock.  You can super glue the shim stock to the side of the fin base, and then trim it with a razor blade and clean up with sand paper. 

You can fit the shim stock dry first and then glue it to the fin with you find the fit.  The shim stock comes in typical shim stock thicknesses and is available from Amazon, Grainger, McMaster, etc.

I tried using sail repair tape on the side of one fin in the past, but it started to walk out. I bet your method is more reliable, but sanding the top was pretty easy too. No muss, no fuss (so far).


Yeah, the plastic shim stock is much more durable than the sail tape.  I cut a piece larger than the fin base and glue it on.  The CA glue with activator is best, but regular super glue works if you give it time to dry, given the large area.  Once the glue dries, I trim it with a razor blade and then sand the edges.  It really only takes a couple minutes once the glue is dried.




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