Re: would moth balls keep a cat out of my boat?
Cat's unlike dogs are a lot harder to control, you can't put up a fence for a cat, etc. There are lots of non-harmful ways to keep a cat away and just because a neighbor's cat is in your yard doesn't mean it is the stray that is getting into boat. There are repellents you can use, i also hear citrus is a good way to keep cats away. Granted I let my cat roam around and he has left some presents in other peoples yards, though he does a good job at keeping the mice, rabbits, and snakes at bay. I would rather have some poo, which can help your garden than have a rabbit devastate it. My cat also keeps those darn birds at bay that like to stain my deck white.
Keep in mind that animals will go to a place they want to, if you make some where else better or make it more hostile than the alternative, then that is the best way.
My cat nor any other cat has got into my boat. A stray will more likely find a home in your boat as a house cat would prefer the warmth of it's owners home.