Cruise ships have many different assets:
- In the ocean (zombies do not swim)
- Mobility (sail anywhere you need or want)
- Very good visibillity
- Carries very large amounts of food, water supplies, etc.
- Onboard desalination plants (no need to carry water at sea/usable on shore to provide land bases with water)
- Fair potential weaponry (fire axes, heavy tools, other improvisational weaponry, etc.)
- Luxury (you'll be able to live out the apocalypse in style)
The nautical experience necessary to steer and maintain a cruise ship is admittedly rare. However, if it can be found, it is potentially possible to steer the ship near potential resupply points, such as abandoned docks and harbors, or deserted islands.
A potential drawback is that a cruise ship with a large number of people on it prior to formal physical inspection will likely have several infected on it that have been hiding their symptoms prior to total transformation. The large number of people that is expected to be in those ships seeking refuge, even if no one is infected, would quickly use up the supplies in the ship (a cruise ship carries large amounts of food for a large amount of passengers). A relatively small group of survivors would be incredibly lucky to find a well-stocked, running cruise ship with few to zero passengers. Another drawback is that the tremendous amount of specialized fuel that a cruise ship requires to travel. Not that a stagnant cruise ship is useless as a shelter by any means, but if one gets stranded hundreds of miles out in the ocean, it can be a death sentence completely unrelated to zombies. And if your ship's desalination plant breaks and you didn't bring any water along, expect mass deaths from dehydration.
It is advantageous to use a ship built as an ocean liner for your base. Ocean liners were built to sail through more dangerous weather than modern cruise ships, as liners need to make regular trips across the ocean with as little delay as possible. Ocean liners are also faster than modern cruise ships for the same reasons. Most ocean liners are now cruise ships, but there is little outward difference between the two types. Without a functioning internet, you'll probably need an expert on ship construction to tell. There is one ocean liner still in service as a liner - the Queen Mary 2. She makes trips across the Atlantic Ocean for part of the year, and the rest of the year, she serves as a cruise ship making round-the-world cruises. As one of the largest passenger ships and faster than any other ship of her size, she is an excellent choice for a mobile base.
Please note that as with all large seagoing vessels, a ship such as this could require at minimum dozens of trained and experienced crew. When underway, and functioning with a full complement, the vessel could require hundreds to keep the ship functioning optimally.