On commercial ships, I doubt there's any full-time IT position since they really try to go almost crewless in order to keep costs to the bone. On cruise lines--you are looking at something arguably worse: A combination of the 'hospitality industry' and shipping, each of which generally believes that pond scum can be whipped into working harder and for less money, and easily replaced if they object. A lot like corporate IT in many ways--but you don't get to go home at night, you get a bunk bed in a shared cabin, indoors, below decks, with instructions not to fraternize with the paying passengers.
It depends what you're willing to put up with, I suppose... Some people don't mind shared quarters in steerage if it means an interesting and varied job.
IT positions on cruise liners and mega-yachts certainly do exist and will become more so as ships get bigger (thinking "The World"
and things like that).
One thing is for sure - your typical "IT" role might be only 5% of the job, so if that is all you're good at, forget it.