Re: Some Basic Info Is Needed...
Cats do have a problem with falling in the water. If you are at the dock, they do not understand the boat moves and can miss a jump ashore or onto the boat. You should have a very large (2") line over the side so it can get back aboard. Netting could be a really great option, though a lot of work. We lost a kitten overboard on a trip to Hawaii; it was so sad.
Kitty litter is a huge problem. It gets in limber holes and pumps and as it is clay, it kinda gunks things up. I have tried to use the crystals instead.
All that said, I had a cat aboard my boats for 18 years and she did OK. Though she'd never lived ashore, I'm pretty sure she always dreamed of a life ashore.