Yeah Wot - I thought I was seeing double...

I'm no expert on gelcoat, but my .02. Fiberglass needs a coating to fully waterproof it and protect from the elements. Gelcoat works great, but is hard and brittle, so it chips and cracks whereas fiberglass will flex a bit.

The cracks originating from the screw holes may just be from improper drilling or tightening the fasteners too much. However, the fact that they've traveled so far may indicate you've got some flexing going on back on the transom (which would also explain those around the swim platform). A one time big bump or overload of the platform could also be the culprit. Either way, I'd check the transom for stiffness and flex in case the glassed in plywood has given up - otherwise you risk the cracks re-appearing after any repairs.

I'd consider any stress cracks above the waterline as cosmetic (fix em if you want), but definitely repair those below. Constant wed/dry hot/cold cycles can cause the gel to delaminate and flake off. Gelcoat repair is like good auto body work - an artform. Not necessarily hard, but difficult to do right. Lots of books and articles on the web, but the real basics are: wipe on a marking solution to show all the cracks, grind them down to the glass full length plus a little, mix to match new gelcoat (the hardest part), apply (use waxed gel or cover to cure), block sand, repeat gel application if needed, sand, compound, polish.

The good news is it's the off-season for boat repair & you might be able to find a hungry glass man. Good luck.