We've just added a new member to the family, and will need to put a litter box on the boat. Looking for innovative ideas, or someone with experience.
You said you wanted innovative ideas!
What's pictured below is really possible. We have stowed a small bag of litter to use in case we're in a situation where the weather is rough and Donatello has to go, but can't because of the wave motion. He is 11.5 years old now and in 10 years of cruising, we've never had to resort to using that emergency cat litter. He seems to have developed a travel routine of using the toilet just after eating his breakfast in the morning, but before we get under way (which is rarely before 11:00). He's then good for the next 5-8 hours of travel. As soon as we dock, he finds his way to the toilet again.
We may find, as he gets further on in years, that we'll have to switch to a litter box. Cats become less agile with age and can develop kidney issues that require more frequent urination. Our last cat lived to be 23.5 yrs and, thankfully, was able to use the toilet up to age 22. Then we had to switch to a litter box.
So, with the pictured method, there is no litter tracked around and there is no smell. Best of all, no litter box to clean out every day. There's a tradeoff, however. It's about like having another human passenger on board, as it generates more flushes -> more frequent pumpouts.
https://www.amazon.com/How-Toilet-T...o+toilet+train+your+cat&qid=1616403477&sr=8-1
We first trained our previous cat (the one that lived to 23.5) at 6 yrs of age. Our current cat, Donatello (the one in the picture) we started training at about 6 months. The book does a very good job at explaining the process. The best scenario for training is at home (and hopefully your home has two bathrooms, which makes the process less inconvenient for humans during the training period). Once training has been completed at home, we've found that the skills are portable. Hotel = no problem. Boat = no problem. At first, we were not expecting the cat would ever adapt to a marine toilet situation - and we were pleasantly amazed when he did.