Posted April 21st, 2010, 08:59 AM
Fixed ballast, very wide beam, high cube design, water ballast, are all elements that combine to give a very stable ship with a draft of less than 26 feet in most cases. The deepest draft ship running until recently was the old Regal Empress which drew at least 32 feet. She was built in 1953, so that makes sense.
The modern cruise ship is flat bottomed and slab sided. This is why they are very stable.
A very good discussion about this aspect of ship design can be found in George W. Hilton's book Eastland: Legacy of the Titanic. The Eastland capsized in the Chicago River in 1915. It is out of print, but should be available at Amazon or ABE Books.
My first cruise was on the regal empress when she was the caribe I back in 1989.
Anyway like most have said here these ships have huge heavy keels google for some pics of some of these ships in dry dock you'll see.