We have two cats at home, but we have not had them on the boat yet. In my opinion the best cat litter is called Cat Attract, but it cost a little more than the others. It clumps very good, and that makes a difference in keeping the smells down. There are also sprays available that can be put on the litter, that sweeten or kill the smell of the litter as it gets older.
I think when you decided to take an animal on a boat, there are going to be adjustments to be made...just like with any crew member. If you have to take a cat on the boat, then you need to get that cat good litter...this is an area that I don't think people should be skimping on.