As far as the legality of FRS radios...

Cruise ships are usually of foreign registry, so while on board, you are subject to the laws of that country (and the country is seldom the US). FRS radios will probably not be legal in that country, and if so, they would be illegal on that ship. If your ship is registered in Europe, Europe has a radio service similar to FRS, but would require buying those radios, which would then be illegal to use in the US. In short, probably not worth the bother.

Maybe now would be a good time to get an amateur radio license <img src="images/graemlins/cool.gif" alt="" /> Only $12 for the test (plus $20 or so for the study book). Then you can get a 5-watt radio which should be legal anywhere (provided that you get the permits from the registlry country ahead of time).