If you are worried about that crack around the whole boat, don't be. The deck wont fall off. that is where somebody attempted to cap your rub rail gap.
The only way to fix this though is to ground out the whole crack and re glass( NOT BODYFILLER) prime and re paint. If i were you i would just slap a rub rail back on.
Thank you! What if I just repaint the boat and slap a rail back on would that be ok? I don't have money for good paint job just was going to spray it with a gun