Could not find the post about the emergency rudder
so I am putting it here.
My boat is 28 feet and 7400 pounds with a sqaure transom and a transom hung rudder
The rudder in the water
is 42 inches X 15 inches, above the water
it gets more narrow ( front to back ) to about 6 inches where the tiller bolts on. It is 2 1/4 thick at the thickest part, and a 0015 NACA foil section. The leading edge at the bottom has been rounded. There is also 17% forward of the balance point. That would not be required for an emergemncy rudder. The greatest strain appears to be next to the lower pintle.
The internal frame is plywood
and that is covered with three layers of cloth. More would be better.
My next rudder which may have a small sekeg in front of it, will have five layers of cloth and a hardwood interior