Coosa Bluewater is a fiberglass-reinforced foam that is 100% rot-proof. Cons: Significantly more expensive than wood.
Only use Marine Grade Plywood (like Okoume or Meranti). Never use pressure-treated wood, as the resins often won't adhere properly. 2. The Composite (Coosa Board) Upgrade
Remove the outboard, trim tabs, scuppers, and the aluminum transom cap.
Chisel out the rotten wood. On older Gradys, this often turns into "mud".
Butter the new core with thickened epoxy or polyester resin, clamp it into place, and glass over it with layers of 1708 Biaxial Cloth .
The only way to be 100% sure is to drill small exploratory holes from the inside . If the shavings are dark, wet, or smell like mulch, the core is gone. 🏗️ Repair Options: Wood vs. Composite