Another article from Howie on water retention in Sunfish. If they take on water the water needs to be drained immediately and leak repaired. Otherwise the foam inside soaks up water and is hard to dry out.
FMI: Overweight Sunfish
This picture is of a hull repair in progress. I made a backer patch and slid it inside, epoxied it into place and pulled it tight with string until it dried. Then I added 8 layers for fiberglass mat to rebuild the hull. Once dry I used marine tex for a finish coat, sanded and painted.