Depending on time of year, you can see Southern Cross from Caribbean. Just check a star chart. Also, around time of new moon it will be easier to find.
Definitely can see plenty of stars from the ship. I recommend bringing along a star chart or ask one of the ship's officers to help you identify the stars.
"The test of a first rate intelligence is the ability to hold two opposed ideas in the mind at the same time and still retain the ability to function."
F Scott Fitzgerald
Seven Seas Navigator (12nts) - San Francisco - Vancouver - May13
Silversea Silver Explorer (23nts) - Kangerlussuaq, Greenland - Nome, Alaska - Aug 14