No different from a land bar. If you are obviously drunk, the bartender/waitress has to 86 you. Just because you are at sea, does not mean that you can get "more drunk".
Now it does become a little trickier since you are at sea where Maritime Law comes into play.
"Did intoxication play a big role in what happen?" asked Brett Rivkind, a Miami maritime lawyer who represents the Smith family. "And if so, then you need to look at maritime law and legal responsibility, which holds the cruise line responsible to adequately supervise the serving of alcohol and alcohol consumption aboard their ship."