Pick up the west systems manual $3 and read about replacing transoms. You'll need at least 5 gallons of resin and 2 4x8 sheets of marine plywood . . . 2 sheets of marine ply will give you 3 layers. Also get a big bag of cabosil/aerosil.
Do NOT buy west systems resin and hardener . . . it's marked up 500%. Order resin and material from
www.uscomposites.com