Hi Simon

It may be just the paint cracking a bit, if its on both sides of the beam, and is on the rear beam, theres a fair bit of twist occuring at the rear beam, but I guess theres movement at all beam mountings, especially a mossie with its smaller beams.

Beam bolts - I think firm, but not over tight as you will damage the bolts and make them hard to remove when you want/need to. Without really knowing the right answer, I would say if you've had the beam bolts undone at any stage, do them up firmly and after been for a sail I would check them again. Not sure how often they need checking after that, as much as you like I guess.

Sorry just re-read your post, being the main beam, but I still think it applies anyway.


Regards