Glassing Wooden Fins

I’ve searched the archives, but I still have a question on technique for glassing wooden fins that are made by the method of sandwiching two wooden panels with a fiberglass layer in between. Here is what I am thinking of:

Would it be best to glass each side as pictured above (with laps), or let the glass layers ‘meet’ in the middle and extend out like so:

I’m thinking that the 1st method would make for a better approximation of the wood foil without having to ‘refoil’ after glassing (except for cleaning up the laps), like would be needed if glass rope were to be used as a ‘halo’ around the fin. Also, the fins will be angular, ‘747’ type fins, so many relief cuts would not be needed (except the corners), as might be on a strongly curved template. Any advice would be greatly appreciated.



Hey John,

the glass layer in the middle will not do any mechanical work for the fin as this is

a maximum shear zone and not a tension/compression zone. I’ve been making those

wood keel fins for over 3 decades and the easiest way is to meet the two outer

layers around the perimeter without any lapping. One hint is to make your wood

blanks with a blunt edge, that way you will end up with a slight resin/glass bead.

Hope this helps,



Thanks for the advice and pics, I’ll give it a shot. The main reason I am using the glass core is mainly to have a ‘centerline’ to foil from (I have never foiled fins before, so I need all the signposts I can get), and for frontal impact strength. I was thinking that the center glass panel would be a good reinforcement for run-ins with rocks, doorframes, truck beds, tailgates, etc.

One question though: do you glass both sides at once, or one at a time? If one at a time, how do you keep drips from one side getting onto the other side and showing up as bumps to be ground down later?

Thanks again; I love this forum.


PS- Is that a fisheye lens on the second pic, or a series of undercambered fins with a symmetrical foiled ones in the center? My guess is the former, but it would be cool to see what differing amounts of undercamber could do to a board’s handling!

Hey JSS,

The easiest way to glass the fins is one side at a time. (there are ways to do both

at once, but the keels must be reverse-nailed to a mount = hassle) esp first timers.

Find a flat clean expendable surface. I use masking paper, but DO NOT use newspaper.

I like to tape the paper to the table at the corners to maintain tightness.

Lay pair of fins about 1/2 inch apart along the bases. Glass both outsides or insides.

The two keels should make a heart shape kinda.

Lay a big square of 6 ounce cloth so there is at least 1 inch safe margin around the pair.

Hint: use a 3 inch chip brush, no squeegee. use lam resin, pretty hot (wood inhibits the

cure a bit).

Brush out your resin sparingly so there are not too may drips running off the fin and down

the excess cloth. No puddles but move quick, I got to the point where I pour dollop in the

middle and work it out.

Big Hint: use your wet brush to “tack down” corners of the big square cloth to the paper

on your table. This pulls the cloth tight like a tent or a drum head. Tack down areas so

the cloth coming off the fin are exiting off the fin like you want.

Now, brush resin around the leading and trailing edges, so you have about 1/4 inch of wetted

cloth out past the wood fin. (this will act as your “dam” when doing the other side). Be clean

and try to be precise. Give time for the cloth to wet out, don’t push down and force it.

Look really closely for any pinholes in this 1/4 inch overhang. Try to brush them away as

your resin starts to thicken.

Be sure NOT to over-wet the fin panel areas as the cloth can “float” and change your foil.

Once dry:

I use my glassing shears (they won’t dull doing this) and trim out the fins. I start by cutting

a rough outline (paper AND cloth) then go back and get my 1/4 or 1/8 inch extension looking

the way I want.

(I DO NOT separate the two keels, the bases remain 1/2 inch apart, it makes handling easier).

Repeat the paper, taping, glass square, brush out, etc. Then, toward the end, use your

brush like a stippling tool to force bubbles out of your leading/trailing edges. A light bouncing

touch will wiggle and coax most bubbles out. I wait until the resin starts to thicken- I have

about 45 seconds to go all around the edges really before gelling starts and the brush can’t

be saved.

Trimming the second side entails cutting the two fins apart using a Utility knife and trimming

flush at the base. I use my shears to get within about 1/16 inch from my final edge.

I use a high-speed (11,000 rpm) 5 inch grinder to form the final edges just right.

Now I wished I posted some build pics- I should take some! (fingers are tired)

Hope this helps,



No pics necessary (can’t speak for Chipfish, of course), the explanation was great and very thorough. Time to bookmark this thread for future reference! I’ll be starting on my fins in a week or two.

Thanks again,



Here is a really good thread from a few years ago.



Yes, that thread is wonderful, and first gave me the gumption to try my own fins someday. The only thing that I don’t like about the method is the amount of re-foiling that has to be done after glassing, with that much fin rope around the leading/trailing edges. I suck at sculpting, which is essentially what fin-foiling is all about. on the wood, I have the ply veneers to give me ‘contour lines’ I can use to mark my progress, but a solid chunk of clear glass gives me less to go by, and I don’t think I could make the curves as nicely as I could on the wood itself, without lots of practice.

I have to make 2 sets of fins for 2 paipos I am making for a classmate, one 4’0", one 4’6". I am thining of making the fins small, around 3-4" depth and 5-6" base chord, trapezoidal (like an airliner/747 tail) to make the foiling easier (all straight lines). They will both be twins, with 0-1 degree toe-in, and 0-very little cant. Classic Fish-like.