Hey
I’m planning to make a few fins with the mountain of left over fibreglass that I have from laminations.
I’m thinking of doing the normal standard fins that fit into standard fin boxs
How many layers should i put in each fin ???
Brian
26 layers of 6 ounce in a hand layup works well for the thruster boxes, which are 0.25 inches wide on the flange.
36 layers of 6 ounce for the Fins Unlimited boxes, which have a 0.375 inch width.
Each layer of 6 ounce is about 0.01 inches. You can sand the flange down, or add small snippets of glass to beef it up, if you are off by a little.
The archives at Swaylocks have TONS of info on fin layups, and grinding/sanding foils on fins. Use the search function…
Laying up fins this was is a humbug, and trying to get them “just so” with regard to thickness for fitting a box or FCS system is a major humbug. I’ve tried. I don’t do it any more, for boxes; only use this technique for glass-on fins.
I’ve found the quickest way to make a nice fin is three layers of mat with a layer of 1/8 inch mahogany 3-ply on either side. Precut the mat and wood about 1/4 inch oversize on all sides. Cut the ply so that the second layer will go up the fin rake when it’s foiled. Lay down one ply, wet with resin, lay down and wet a layer of mat, making sure to work out the bubbles. Lay extra resin and then the second mat layer. Wet out, repeat for third layer, then lay on the second ply. Try to line up the two layers of ply within the 1/4 inches extra you cut it out with. Stand back and let every thing cure.
Note: gotta use catalyst since there’s no light between the layers of ply.
A fin like this will be easy to foil, since most of what you’ll be grinding is wood, not glass. The layup is quick, and with a little tint in the mat there will be a nice halo around the leading and trailing edges. The leading edge will be mostly glass, so it’s adquately strong.
A fin made this way will almost float, depending on how much you foil the wood; might float if you use epoxy.
Two layers six ounce up both sides when you glass 'em on.
Thanks very much Charlie & Blackstah.
Am gonna start experimenting 
Brian
I agree with using some wood. I use 1/4" ply, foiled first, then glassed with 3x10oz volan, both sides.
I make glass bases first. Whenever I’m laminating, repairing, or epoxy-hotcoating, I set aside a little pile of about 15 pieces of scrap volan glass. I use any extra resin I have to set up these little laminated piles, like 2" x 9". Once that’s set, a couple trips through the bandsaw and I have 7/8" x 8" x 1/4" glass fin bases, the same thickness as the wood core. Pop those on with hot glue before laminating the whole pile.
Then heat the epoxy with a halogen light so there aren’t bubbles in the lam…(the lamp does not work with poly resin in my garage in the winter…eh, Schwuz?)
I’ve been making wood core glass-ons for a while, but the base/box thing is pretty new for me.
i know nothing about tri-fins.for singles, use 36-40 layers of 6 oz. volan or 54 of 4 oz.
When I make glass single fins for a fins unlimited [multifins in oz] box, I’m using 50 layers of 5oz flatweave, but it DOES seem to depend on how many layers I do at a time, and how much resin per layup.
I usually do either 10 layups of five or 7 of 7 [8 for the last layup].
... hope this helps !
ben