What happens when the ship runs into stormy seas? Does the cruise director make an announcement, "Ladies and Gentlemen, I regret to inform you that due to (hurricane) (typhoon) (gale-force winds) (you name it) this evening's ice gala has been cancelled"?
I imagine that huge cruise ships have a small amount of "rocking" from side to side, as there has to be some kind of motion while the ship's engines are running. I guess this kind of action is something the skaters get used to. If they can skate outdoors in wintry conditions, they can probably adjust to skating on a ship.