Learning Fin Construction Part I: What shape am I?

I am a TOTAL newbie when it comes to laying up and glassing anything. I know it’s always cheaper and easier to just go out and buy an item instead of making it yourself- especially for these types of projects- but:
a) I want to learn how to do new stuff too (that’s what life’s about, right?)
b) I don’t want to show up at the party wearing the same old outfit as everyone else
c) It’s just neato to see something come into finished form as you work through a project

The downsides, however, are that for these types of projects, PLEASE use extreme care when working with any tools, chemicals, or materials. They make safety equipment for a reason, and it ain’t for show.

My better, more talented half has been doing some small fiberglassing projects for a while- for a boat, for board repairs, etc. But, both of us wanted to try making a “practice” fin since fins can be very creative, as well as a compact project for a hobbyist. This is not meant as a how-to, but rather an account of my initial experience doing this- hopefully I’ll get better!
I’ve looked on different websites, but never found anything really showing a how-to on vacuum bagging a fin start to finish. I’m sure there’s something out there, but I’m a total newbie, so it would have to start from the absolute basics for me. I’m sure experts who read my progress will think I’m extremely slow or stating the obvious, but sometimes you just gotta mess up and ‘fess up.
We wanted a simple shape for the practice fin, maybe an old school looking skeg. I really wasn’t going to worry too much about the proportions, but my husband did draw up a shape on the computer that had some nice proportions and curve, and most importantly, had a base (bottom of the fin that meets the board) that was about the same length as some of our professionally made fins. We used a 9″ longboard single fin as a guide to help with overall base dimensions as well as bottom part of the fin that fits into the fin box on the board.
To start off, we figured we’d use some thin craft balsa wood for the core of the fin so we could have a skeleton to build the fiberglass onto. To try to give it some dimension, we concluded that we would make the core out of three layers of this 1/16″ thick balsa, but the two outside layers would be a 1/4″ smaller in fin shape. We thought this may help give the thickness of the overall fin some dimension and mimic curve on the edges (see the term foil).
Since the craft balsa we had around the house came in these thin planks that are about 3″ wide, but several inches long, we cut up the planks with a pen knife and glued them together by the thin edges to form a greater surface area on which to draw the shape. We used carpenter’s glue and cling wrap to protect the wood and put books on top until the glue had dried.

Measuring the pieces to be glued side by side

After the three larger surface area pieces’ glue seams had dried, and handling them very carefully, I traced the fin profiles onto the balsa with the grain going up and down in relation to the profile. I also made a pattern for the fiberglass profile that was 1/4″ bigger than the wood pattern, and included a long rectangular base in that pattern- extending longer that the front and back of the profile of the fin- about 7/8″ down from the bottom of the edge of the wood profile pattern- this box area would become the part that you mount into the board, but made only with fiberglass, no wood core. This came from studying the fins we already had and measuring those.
After tracing, I cut the balsa core shapes out with my scroll saw:

Finished cutting center piece

After cutting each piece out, I gently went around the thin edges with an old multi-grit emery board of mine- don’t laugh, it works- and gave a little roundness to the edges so they weren’t super sharp.

Gently sanding the edges of each balsa piece
All pieces cut out (left side, center, and right side) ready to be sandwiched together into one fin core


Part II: Glassing Shouldn’t Suck

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