The rudder consists of two flanges (3/8" plywood), a packing piece, and the blade. The packing piece and the blade have to be of the same thickness, 3/8" plywood or 1/8” aluminum.
1. Trace packing piece and blade on the same sheet of ply or aluminum. Cut.
2. Cut two identical flanges by tracing the packing piece and extending the flanges as indicated on the diagram below.
3. Laminate the two flanges with the packing piece.
4. When cured, insert the blade into the space between the flanges .
5. Drill the hole for the pivot (3/8" carriage bolt, bronze) through the flanges and blade.
If yours is a plywood blade, a shock cord attached to the leading edge, and let up to the tiller, will serve to hold the blade down in the water.