Building Rudder/Sealing Marine Plywood
I suppose I''ll put in my two cents.
Plywood is good for building rudders mainly because as you plane off the wood to make the foil shape, your progress will be shown on the glue lines between the plies. For a twenty-five foot boat, I''d suggest you plan to make it 1 1/2 inches wide by gluing two pieces of plywood together.
As far as the shape goes, there''s an old saying: “If it looks right, it is right”. Cut the initial shape out with a jig saw, then get a good and sharp block plane and go to town! Make the leading edge round and try a 5 to 1 taper for the trailing edge. Leaving a small, perhaps ¼ inch round or flat to finish the trailing edge won’t hurt anything. I’m sure there are some who would cringe at that shape but it will work!
What seems like a lot of work will turn to enjoyment as the curls fly away and the shape of the rudder starts to come out of the wood. Be careful here because you may find yourself actually starting to like this stuff and having thoughts about building your own boat!
Once you''ve shaped your new rudder and sanded it fair, you can coat it in two coats of fiberglass. I''d recommend epoxy instead of resin for this job. WEST, System 3, what ever will do. Paint it with two coats of epoxy then start laying down the fiberglass while the second coat is still wet.
Once the glass has kicked hard, sand the rudder fair again and paint it over. Hang it on the boat and ask her what she thinks! Just take your time and you''ll be proud of the results.