I was an orchestra musician on a cruise ship for 6 months in the late 90s. For the last few weeks, I subbed on another ship and had a roommate who would watch "Titanic" every night with his girlfriend. That was a bit weird. Still, he was a nice guy and great player.
Orchestra musicians would play in the main 1500 seat auditorium with a wide variety of shows including a Vegas-style show, working with magicians and comedians. We had an incredible singer who had the best charts for a set of Sammy, Frank, and Harry Connick Jr tunes. On the nights we weren't playing in the lounge, we'd do a small group jazz set or R&B review in another lounge. As a rhythm section player, I worked more hours than most musicians on the ship, but even then, it was only 14 hours a week. Lots of free time. Not a bad gig really.
The singer/pianist in the piano lounge would hammer away through various songwriter and piano rock material. I don't remember him being the most amazing player or singer, but he had a great personality, could read the room, and sure did rake in the tips.
We also had a Polish string quartet who taught me how to say, "I'm hungover" in Polish.
It was the largest cruise ship in the world at the time and wouldn't fit through the Panama canal. Since then, the canal has been widened and ship designs have changed. The largest cruise ships now are more than twice the size of my ship.
Since my experience was over 20 years ago, I can't say what it is like now, but if anyone is interested in learning more or trying it out, Windish Productions could be a good place to start. http://windishmusic.com/billboardonboard/