Building the foil was the most intersting part of the project, since I'd never made anything like it. There is a lot of information about foil fabrication on the internet.

The foil is a NACA 12 shape, which is a reasonable compromise between lift and drag. The 12 means that the maximum thickness is 12% of the chord (front to back) length. The formula for a NACA foil is well documented. I made the chord length 12.5", yielding a thickness of 1.5". The aft 0.75" is cut off to avoid an overly fragile trailing edge.

After laminating a bunch of cedar 2x2 strips (finished dimension is 1.5") I used an unusual shaping process. Rather than endless sanding and matching to a template, I ran the slab lenghtwise through the table saw many times. Each pass has a different cut depth and angle. A dado blade can reduce the number of passes. The depth is calculated directly from the formula. The angle is the arc tangent of the first derivative at each point on the curve. For each setting, make the cut on both sides to ensure perfect symmetry.

Here is a photo of the partially shaped foil.

After shaping, I sanded the foil, filled in a couple low spots where I had been careless with the saw setting and wrapped the foil in a single piece of 6 oz. fiberglass cloth. Hanging the rudder by the ends made applying the cloth pretty easy. This was my first ever fiberglass project, so I didn't know what to expect. I used West System epoxy over the glass. A bit more sanding and a few coats of UV resistant finish and the foil was complete. I added a 1 inch thick mahogany cap to the top for strength and appearance.

Here is a photo of the fiberglass being applied. Still a little squeegy work to do in the uppr left.