It depends on the size of the ship. I don't remember from my NCL days, but RCCL has a minimum of 2 on the smaller ships, 3 on VY class and I've seen 4-5 for special installations and dry docks. One is always the manager. The only other IT type gig is the ITV (interactive TV), but I don't think that's as well paid.
Two to three is usually fine for the size of the operation. It they run into any serious issues, they bring in the vendors who sold them the systems, or service contractors - who are usually based at the turnaround ports. As I remember, the IT guys don't deal much with the navigational or engineering areas . . .
I just found this blog last week - It's done by an onboard IT guy and is one of the best blogs on what it's like to work on a ship.
I work for Sun MicroSystems, and we have systems aboard the Carnival ships. I board, and repair our systems (Sun) here in Tampa while the ships are in port. It seems to me that there are usually two IT people aboard, however these are not the largest ships. I think about 70,000 tons are the largest they can get under the Sunshine Skyway Bridge in order to get in to the Port of Tampa. Good luck!
I never really considered it from the shoreside support point of view. How often would you have to board a ship to maintain the Sun Systems. Would it be more hardware maintainance, or general SysAd stuff?
Without revealing too much about Carnivals systems ( which I assume you're not allowed to ), what would your typical maintainance event consist of? How does the systems being aboard ships compare to the land based systems you maintain? Does the fact that the systems are aboard moving vessals affect your job much?
I suppose the ships standing still when you do your job, but I'm just trying to imagine racking a T2000 in the open seas.