No, this is not a gel coat nor a laminate issue. The Hunter 170 is truly a plastic boat, not a fibreglass boat. Read the description from Hunter
When I was looking into boats I didn't give serious consideration to the 170 due to the unproven technology. Basically it is just a plastic outer shell with a spray foam lining. My guess is the cold made the outer shell brittle, there may have been some moisture in the foam or just a difference in expansion of disparate materials and "CRACK".
Basically you are in need of a new boat.