Wow, that sucks.
A lot of marinas will tell you that they are not responsible for any damage to your boat. You have to take the responsiblity to make sure it is properly moored and that everything is secure for anything that might come along. The marina is responsible for is the ground takle, chain and bouy. However, I believe a simple phone call would have been in order.
If your leaving the boat for an extended period an easy insurance pratice is to simply wrap and tie the rolled up Genny with a short piece of spare
line.
Edit: (Too Late, the Dog and I think a lot alike)