what causes this

Fiberglass boats are made of fiberglass cloth and resin (all different kinds of resin) the reason they crack is because resin by itself is a lot like cheap plastic, it has no strength what so ever, the fibered glass is where the strength comes from, the resin just freezes it into the desired shape (a little bit like the cement in concrete).

Stress cracks can happen for all sorts of reasons, but "stress" like Ralph says is numero uno....LOL


Most of the time stress shows up in areas of complex angles or where the area has a lot of resin and gel coat thickness above the first layer of glass, whether it be matt, cloth or roving (and in some cases choppered in)...You have to remember the colored and polished surface you see is the first process of the hull build because the hull is built in reverse (in a mold) so it is very easy to get things too thick, especially in the corners...(a convex becomes a concave and vice versa)..

What do I win?   

GT

nothing yet down boy down can or will it do anything (besides look like shit) that will cause any kind of failure

thanks GT I tryed to put up some pics but it says my file is 2 big so I need 2 figure that out 

Ok so i've been lookin at my boat and i dont no what 2 think about these cracks and it seems like more than just that 2 me so i dont know how 2 go about it i dont want the boat 2 fall apart so I wanted 2 see what the pros thought about it sence everyone around here thinks its ok   Big thanks on all your feedback

cant really tell, but if the white in the 3rd pick is in relation to the crackes in the other 2 pics, that is delamination and should be tended to.

x2

IT Looks like someone tried 2 get rid of them b4 by repainting it becouse the paint has alil bloch were it dosent match and yes the white in the third pic is on the inside of the boat would delamination be the cause of this or would hitin something cause it or both. In any case how should I go about repairing it? thanks all of u

Thanks 4 the info Ralph. So what caused it is it delamination becouse it looks like its just chiping of it dose'nt look like its hit anything.

i do not know

one more thing, dont be afraid to go all the way through the hull when you start grinding

A little trick I have used many times. Before you go all the way through, throw some mat and resin on it then grind from the other side (if accessible)...This not only makes an incredibly strong repair, but prevents you from having to reinvent the angles and contours...

GT

  X2, that is what I did with a crack on one of my chines that had a crack. I by no means am a pro at it, or the experience, but it sure was easier, than what I heard it couldve been.

 if your not joking about being pro at it.. ill pay you to fix my hull! lol