Building a boat out of plywood is not possible without fiber mat and Epoxy Resin.
Epoxy is an easy to use chemical compound that becomes very hard and strong especially in the connection with fiber mat. You can use in almost on any material that do not have a surface which is 100% smooth. It works perfectly on wood (boats) concrete (swimming pools) and other stuff with a slightly rough surface.
On the other side, it does not stick at all on smooth plastic foil or pvc surfaces. So you can use plastic foil to protect the floor and plastic or rubber gloves to protect your hands.
After I bought Epoxy for the first time, I wanted to test the strength of it so I glued two battens together and let it harden over night. The next morning I tried to break the battens and they would break anywhere but not along the seam with the epoxy. Very impressive.
However, Epoxy is a toxic Chemical! If you open the can it smells very bad. Always work with epoxy in well-ventilated areas or outdoors (best). Wear protective gloves and a mask when working with epoxy or when sanding the boat.
Do not breathe the dust and don't get epoxy on your skin.
It can cause allergic reactions and skin irritations. Keep it away from children. Handle with care!