To cut the bevel on larger fins, I use a tenon fixture on the table saw. This fixture shown here is made by Delta. A tenon fixture is a heavy cast iron base plate with a rail that fits the table saw's miter slot. Attached to the base plant is an tiltable face plate that holds the work. An integral clamp holds the work.
Here is the fin clamped to the tenon fixture.
Copyright © Thomas Fetter
The tenon fixture uses a threaded adjuster to precisely position the work with respect to the blade. This makes it very easy to adjust the work so that the bevel is centered on the thickness of the fin.
The tenon fixture's faceplate was not long enough to support the length of a fin, so I added a longer 3/4 inch plywood faceplate to support the fin along its entire length. If the fin is not adequately supported, it can flex while being cut, and the bevel will not be precise.
The tenon fixture face plate can be tilted, so I use this rather than tilting the table saw blade. Here the tenon is tilted at 10 degrees, the angle I commonly use for my fin bevels.
Here is a close-up of the bevel cut.
The finished fin with all bevels. The next step is to fiberglass each side using a vacuum bag to ensure the fiberglass conforms to the bevel.