it depends. There are deck "plates" that separate from the rest of the hull on the inters. Getting them off and sealing the new ones isn't east though. If you've got substantial cracks (not just gelcoat) in your hulls then you should really be taking it to someone who knows what they are looking at becasuse it could be a case of structural failure (reference H20 hulls "cracking" around the front crossbeam back in the day)