Looks like those linear cracks are caused by flexural strain...............but fixable. If you want to repair these yourself do an internet search on "repairing linear gelcoat cracks" for repair methods OR hire a gelcoat guy.
My concern is that the cracks are an indication of flexing. The question is: is the flexing caused by the mast, jib track or something else? A gelcoat repair is certainly the cheapest and easiest band-aid repair, but there is a good chance you will end up with the same results.
I don't know how you would figure it out, but you really need to know what caused the crack in the first place. If there is some play with the below deck mast support, maybe some shims. If it is the jib track, then it would probably be best to attack it from the ceiling below. Take out the balsa wood core and replace it with glass.
There are more questions than answers, so you may want to get an expert opinion.