I have been talking to a very interesting acquaintance of mine this afternoon, he used to work on cruise liners for years. He got me thinking about the point of balance because he informed the gathered throng, sitting around in his garden, about an American, middle aged chap, who for exercise each morning, would Unicycle around the deck a few times. Apparently, this guy favored the pitching and bucking of the ship in foul weather to calm, orderly riding.
This entire image started me thinking about how hard that must be, or is it? Anybody on here have experience of riding a unicycle on a moving platform of some design…? 
No experience of that, but I can’t imagine it’s that difficult once you get used to it - especially given that the movement of a large ship is relatively regular and predictable. Certainly no harder than muni where the obstacles are far from regular and predictable.
I knew a guys who did shows on a cruise ship, with unicycles and bicycles. Mostly his challenge was fitting his act onto the relatively small stage area, and under the low ceiling. Like when he did the headstand on the bike’s seat, he would have to have his legs bent to not hit the lights.
My experience on cruise ships suggests that they are pretty boring in terms of movement, since mostly you can barely detect it. I remember one day of rough seas on an Alaskan cruise, where the pools were splashing around like a disaster movie. That would also be the day I’d like to ride around on a uni.
I’ve ridden in elevators and escalators, and I once did a show on a small boat (small show for small kids), but the boat was tied up in the marina. Not too much movement.
On a unicycle, your point of balance is always in motion (same as when you walk), so it’s something you have to “chase” to stay on control. Mastering it, I guess, is being able to plan ahead and move the wheel so that it will move your point of balance where you want it. 
Fascinating subject though… Thanks for the answers guys, at least I can now go back into the discussion loaded with info… !!
Once I did a unicycle performance on a smaller cruise ship during a storm. I needed a few minutes to get used to but after that it wasn’t that hard. But on a small ship/boat I imagine it to be very hard as it seesaws much faster an less predictable.