Micheal,
Welcome to the forum. Great to see another Mozzie racing in QLD. Hope you enjoy the experience as much as the rest of us. I believe Ben Cutmore was the last owner of your Mozzie so it has seen some serious racing in the last few seasons. Just a couple of questions for the register: Did you re-name your Mozzie ? Do you race from Bribie Island Yacht Club ?
I agree with Rob; it's just flexing of the paint that has caused the cracking. It is also usually seen on the deck where you normally sit.

Maybe someone was sitting in front of the front beam which is not uncommon in very light winds.
When you get around to repainting then use a thinned 2 part epoxy which will sink into the timber and make everything alot stiffer. I did my decks a few seasons ago with Everdure and haven't seen a crack since.
Regards,
Peter