This has been siiting up in my garage rafters for at least three years now.
I can’t even remember why it got sidelined. There must have been more pressing short term projects that got the better of it. But all of those are now done with, and it is back on the table.
6’3" x 21" x 3" single fin. I had planned to fit it with a fin box, but now past experience has taught me that over time, and with enough use, these can be a source of leaks. So I will be going with a glassed on Spitfire outlined fin instead.
I used a double internal stringer, instead of a single one, to help minimise twisting of the frame when the bottom skin is being glued on. Top skins will go on next, and then the shaping of the rails will commence. Hopefully I won’t get distracted again.
I never faced a problem with leaking fin boxes, but I do not reinforce with foam, but with balsa blocks. A solid balsa block glued in with contacs to bottom and stringer will hold, if with additional contact to deck it will definitely last forever. I would be more afraid with a glassed on fin, because any damage will harm the glassed area and I judge the chances to leak then much higher.
I usually do longboard fin boxes only, but even with the old fcs sidefin cups, there was never any problem if set into a block of balsa. the weight of balsa will not significantly increase the weight of your board, which looks like some kind of redwood.
Thanks for sharing your experience with fin boxes Surfdude. You’re probably better at fin box installation than I am. In the past I’ve found the tiniest bubble, in the wrong spot, in the resin surrounding the fin box, can lead to maybe not a full blown leak, but intrusion into the surrounding wood, and it can slowly move from there. Once bitten, twice shy. I will glass the fin on strongly enough to withstand a meteor impact. Plus I like the look of a glassed on fin and the board will never travel, apart from in the car. The board is Paulownia.
That’s clean gdaddy. I got a Brewer gun stashed away that is an easy 8 out of 10 except for one thing; the fins. Some “hack” routed the fins in and did a really poor job… In fact it doesn’t really look like the hack used a router at all. Maybe a kitchen knife?? I figured out though that I could refitt it with Futures and the flange would hide the muck up around the base.
It’s good to see that you are going to go ahead and finish up. I’ve got too many projects around my shop that are half done. Had you thought about using " J Foam "? The grey green construction grade foam?
I installed high density inserts into that eps blank before I shaped/glassed it, that being a trick I learned from the compsand guys (Thanks, Sways). . So those fins are supported by 4# PU foam. They’re not going anywhere. I don’t even use a finrope fillet at the base, I just seal the seam with some resin/milled fibers.
I can only imagine how solid the install would be in an HWS if they used a balsa or pawlonia insert.
I did consider routing and setting the fin for extra stength instead of using a fin box, but I fear it will indeed be a hacks job, given my non-skills with machinery of all kind. The foam currently there is blue construction grade XPS.
I thought I might try the following method that Bill Thraikill generously posted here some years back now.
"Guys,
In 1960 I abandoned the use of rope, or roving, when mounting a glass-on fin. The STRONGEST method, as described in part by Balsa, is to use staggared layers of glass cloth. I would use six, or even seven layers, on each side of the fin, using care to make the junction of the fin to bottom surface of the board, as tight as possible. The ‘‘secret’’ of exceptional strength, is to cut the cloth on a 45 degree bias. This puts twice the amount of fibers up the side of the fin, at that junction. In pre leash days, glass-on fins would routinely break on a trip to the beach. After adopting the above method, I NEVER had a fin crack, or break off. Today, with the leash in universal use, that level of strength may not be necessary, but it’s available if you want it. It’s not a method that lends itself well to a production environment, but great for one offs. It’s a method I still use to this day."
I believe I will too Bill. Many thanks for sharing your method here.
Your single fin positioning methodology, which has proven to work perfectly for me, will also be put to use. If not for it I probably wouldn’t have the confidence to go with a glass on fin to begin with. I love how it easily accounts for tail width in the positioning of the fin. Just choose a sensible fin height, and the rest is easy.
