Not a cruise ship, but my brother-in-law is captain of 98-foot yacht that he help design and build in 2004. Since then, he and my sister had invited me on board during one of the (frequent) periods when the owner and his family aren't using the boat. I finally got to take them up on it last year.
I was expecting great DX, but the reality was just the opposite. The radar, sonar, and other electronics create a ridiculous noise level on deck....while below deck, the superstructure blocks all AM signals. Even if you're within sight of the stick. I've heard the cruise ships are pretty much the same thing, except that you might be able to get physically far enough away from the noise to hear something.
That has actually been my experience on the ferries that run from Vancouver to Sydney (Victoria), BC. The journey lasts a little more than 90 minutes, and outside on the top decks reception is pretty good. These are big boats and very comfortable . They hold over 600 cars, and IIRC, can also handle about 2,500 people on their 3 or 4 decks. (Great views, too).