I''m a ham radio operator as well as a sailor so maybe I can help. AS in sailing, there are a number of variables to consider. The frequency you are operating on, antenna, atmospheric conditions, time of day, and type of signal you are listening to (morse cose vs voice), all impact your question. Without getting too involved, your communication can be world wide under the right conditions. Your interest in listening to the Caribean area would make me consider 14mHz band (20meter band) and you will probably have the best luck near sunrise and sunset times of the say. You should have good listening. Good luck.
Phillip Wilson, N8IPS