Water can get into the bilge through the mast and down the compression post. There is a weep hole in the deck plate that often is obstructed so the only place for the water to go is into the boat.
The photo below is the bottom side of the deck plate. If you look at this from the top, it looks like there are a number of weep holes around the sides but those objects are simply cutouts for the bolts. The weep hole is the small grove at the top o the picture. IMHO: It is too small and gets blocked easily.
From Mike and Morning Glory