A:Answer I don't see why they wouldn't be. These work by relaying the radio transmission between the two radios, so no external relay antenna is needed. Each radio is acting as it's own antenna. Plus, a cruise ship is pretty small compared to the distances I've been getting out of mine, which is 4 miles. Now, that being said, I am not sure if the cruise ships have any policies against two-way radio communication due to the fact it may, or may not, interfere with their communications with ports-of-call or other ships.