i would be checking the centre board case more throughly. on our 18 we took a fair bit of water through the case. when the boat is moving the case act like a pump put great pressure inside the case therefore opening the cracks. also check under the front beams, i know of a boat who had cracks under the beams. this boat was about 13 years old and the cracks appeared where the boat sits on the trailer. just out of curiousity how old is your boat??