soak some food in anti-freeze, that will fix your problem. Or fill the bilge up with water, cats hate water. Try putting a trap in the boat and catch it, then soak it down with a water hose and it will never come back to your boat. We used to do that all the time. There was some old lady that had about a million cats and they would always get on our cars. I killed a few but I soaked most of them and they never came back.