Any thing to worry about?

I have a used Hobie and there are a few cracks in the decks. One is 12" long but doesn't seem too deep. Nothing seems to have any give to it. (You can also see some very small ones below it in this pic.) This one is port side in front of the tramp pylon....


The others are more superficial but strange looking on the starboard side aft of the rear pylon....



Should I be concerned?

No reason to be concerned..those are surface stress cracks on the gelcoat not the fiberglass below it. If u want to repair them ull have to open up the cracks with a sharpened screw driver or the point of a knife then fill with gelcoat and sand/buff.
This is only cosmetic, It happens where there is a lot of flexing.

Excellent....I will live with them as most of them are too small and sailing weather up here is limited to only a couple of more months