I have defined them as follows:

Cruise Line/Ship: a ship that leave one port and cruises to another port or spends 12 or more hours on the open sea.

Day cruise or Coastal cruise. A boat that is setup strictly for gambling and must go out beyond a preset limit to gamble (3 miles out in the Atlantic and 9 Miles out in the Gulf of Mexico for Florida, but each state can set there own limits provided they are at least these). Note: there are some cruise ships that have been converted to this type of boat
so size is not a restriction in my definition.

Riverboat: a boat that is moored to a dock or leaves the dock to move into a channel and allows gambling. Does not leave one jurisdiction for another.