Aft Buoyancy Tank
The aft buoyancy tank has a longditudinal stiffener to support the deck. It fits between the aft bulkhead and the transom reinforcement pieces.
Transom Stiffeners
The transom stiffener pieces go in first. The vertical stiffener gives the strength for the rudder fittings and the horizontal one reinforces the transom ply across the boat.
They should be made from solid timber and the corners rounded with a router cutter.
Longitudinal stiffener.
The plywood piece can now be fitted between the bulhead and transom as shown.