If your getting that much water in the hulls, start with all the obvious possible points of entry:
Caulking around the pylons - sometimes the caulking looks good, but upon close inspection you can pull it back with your finger nail.
The Hull / Deck seam - Any small crack might look innocent, but press hard against the hull under any cracks in the seam and see if you can make the crack open more. (Particularly around the side stays)
Rudder Gudgeon's - You could be taking water in through the screw holes. You could try taking out the screws and re-seating them in a fresh new bed of caulking.
Bung's - Check your bungs. Sometimes if you screw in the bungs too tight you can pinch the rubber seal between the bung and the bung hole causing it to twist and not create a good seal.