A crack in the gel coat should not occur while lifting a boat from the mold. Cracks as you described can occur while the boat is beaten in the wind with bad
rigging constraints. While you can repair, unless the basic
rigging questions are addressed and the stress points are taken into question, the crack will reappear. The fact that no blisters have shown yet is moot - it can take a year (or more) for the moisture in the lamination to show.
Best wishes,
MaryBeth