There are a couple ways to do this. The first and best way would be to remove the mast and the deck plate. Let it dry out and see how much permanent damage you have. If there is no damage, you need to at minimum replace the wooden posts under the mast. If there is damage to to the deck, there are two ways to fix it. The first and hardest is to cut that area out and reglass a new area in. The second way is to have a custom deck plate made that is at least twice as big to help support the weight on the deck.
1979 Seidelmann 299