There are some lengthy, knowledgeable threads on this topic at the SSCA Discussion Board in the Communications section - http://ssca.org/sscabb/index.php They are very thorough.
The bottom
line is that you can''t expect much more than 1 NM range unless you start getting quite fancy (and $$)...and even then, more than a few miles is unrealistic. Occasionally, a boat will exceed 1 NM but that may well be because of the height of the shoreside wifi system and the boat using a directional vs. omni antenna.
Jack