I have a 1980s H16, with a 17-20 inch long crack in the bottom of the hull.
Cracks in the bottom of a H16 hull usually mean one of two things- if the crack is on the very bottom of the hull, then you've worn through the bottom from dragging the hulls on the beach and you need a bottom job. Or, if the crack is on the side of the hull near the bottom and in the vicinity of the pylons, then your pylon shoe has likely broken free and needs to be re-connected to the inside of the hull.
The bottom job is a pretty straight forward repair. The pylon shoe repair is quite a bit more involved. In any case, neither of these jobs can be completed by simply "squirting epoxy into the crack". The hulls will need to be glassed, and in the case of the pylon shoe repair, you will need internal access to the hull.
A 17-20" long crack is a major issue and needs to be addressed properly. As others have said, pictures would be very helpful.