a specific point of flex isn't good. fiberglass can take a lot ... but along a specific line a 'back and forth' movement will cause the fibers will fail. think of bending a piece of pressboard (like from a cereal box) along a line and you can see how the 'line of flex' will get softer and eventually come apart. (i'm sure jerry, bob and the other that 'worked in the fiberglass business' can give a better technical description.) anything like you describe would make me NERVOUS on my M17 (or M15, or any other water craft ... esp. below the water line!). look for feedback from jerry and/or bob. sound like a grind and build up new glass job IMO. there was a discussion about trailers i bit ago. some recommended getting rollers to make launch and retrieve easier ... guess your M17 is an example of how easy isn't always the best for the boat. dave scobie M17 #375 - SWEET PEA visit SWEET PEA's www-site - http://www.m17-375.webs.com --- On Tue, 7/28/09, Gordon Gilbert <gordon@financialwriting.net> wrote: I've noticed some cracking on the inside hull of my '83 M-17, and I'm wondering if anyone else has dealt with this situation. There's a single crack, parallel to the lapstrakes, under both quarterberths just under the access hatches -- at about where the boat sits on the trailer bunks. The cracks are about 12 - 15 inches long; one is about 1/32" thick and the other is about 1/16" thick when the boat rests on the trailer. Both cracks appear to close to hairline width when the boat is in the water (which suggests that the hull flexes inward slightly when on the bunks, opening the cracks a bit). I've noticed no water leakage, and there's no evidence of the cracking on the hull exterior. I keep the boat on its trailer and not in the water. The size of the larger crack is prompting me to do something. Should I grind the inner surfaces a bit and epoxy fiberglass "bandages" over the problem areas? Would it be best to do the work when the boat's in the water and the cracks are tightened up? Is there another approach I should consider? Are these cracks just superficial and I should forget about them? Any suggestions/comments are welcome! Gordon M-17 "Sapphire" Milwaukee P.S. Bones and I enjoyed a wonderful cruise to Isle Royale last week. Great weather, fun sailing, beautiful scenery and good companionship. I'll be posting photos soon, as will Bones I expect.