if it is an old school rudder i would take a rounding over bit on a router and do every edge. then sand it to get it allitle bit more like the original. of course this wont work if your planing to race but for a day on the lake should be fine.
First, make sure that your new maple rudder blank is the same thickness as the
original (so the rudder fittings - pintles, and the tiller fittings will fit on it.) Then scribe a line about 1.5 inches in from the leading and trailing edges. Then take a nice, sharp plane and do a little rudder sculpture. The leading edge should be rounded over but still tapered a little into your scribed line. The trailing edge should end up sharper and less rounded. If your finished product looks a little like the cross section of a brown trout with flat sides in the middle, you have nailed it and will have a fairly good hydrofoil with fairly low drag and good steering characteristics. Enjoy - it's a fun project.
Alan, Joe -
Thanks for your input. I have been hassling with this for a while. I got the edges down by using the circular saw on a 45 degree angle. Next comes the sander. We'll see how it works. I guess I should have checked the thickness first though, eh?