"Wm Watt" wrote in message
oups.com...
On Sep 10, 12:00 pm, "Toller" wrote:
My Potter 15 rudder is made of 4 pieces. The top is a solid core about
10"x15", with two pieces of plywood screwed to it on either side
measuring
10"x30". The solid blade mounts between the plywood, below the solid
top.

Those side pieces are called the rudder cheeks. I've replaced mine on
a 21 foot mahogony strip saiboat. They get a lot of stress when
running before the wind with waves comming under the transom and
trying to change your course on you. I just used ordinary fir plywood
without any voids in it. It should be thick and stong. The thickness
might be determined by the hardware used to hang the rudder off the
transom (pintles and gudgeons) although you can rout the plywood to
accept narrow hardware.

Rudder Cheeks eh? What is the piece between the cheeks called?
Mine are 3/8" ply, routed down to 3/16" at the hardware.

What did you put on them to waterproof them?