I had the same problem a few years ago on the second day of my vacation on North Myrtle Beach. I came in from a sail and couldn't pull the boat up the beach so I took out a plug and drained a lot of water out. I lifeguard said he had a roommate who would fix it for me. The roommate owned several Hobies that he used for a business. He turned the boat over, mixed epoxy and put some glass cloth where the crack had occurred then made a channel on each hull with metallic tape. He poured epoxy into the channel so that I have two strips about 2" wide and at least 1/4" or more thick just about the full length of the hulls.. We didn't shape it to match the hull, just left it. When I got home I tried to file it and found it was so hard I quit. It has been that way for at least 10 years and now I check for water in the hulls about once a season, usually finding nothing.

Howard