i've repaired a crack in a hull by cutting a hole for a port in the deck over the crack and working from the inside of the hull. i'd disconnect the hull, cut the hole, lay it on its side, crack down, on sawhorses. clean the cracked area with solvent (acetone?) paint the cracked area from the inside with epoxy resin (push on the crack to work resin down into the crack), then layer 3-4 layers of 6 oz glass cloth and epoxy resin on the inside maybe 2-3" bigger than the crack in all directions. allow enough time between layers for the epoxy to 'gel' before adding the next layer so the previous layer will stay put. you can trowel a thin layer of marine tex on the outside of the crack (be neat! i use an artists palette knife) then sand and fair when it sets up. hopefully the hull is white so you dont have to match colors. add the port, reassemble, and voila! hope that helps-