Strength and clarity are two different issues from the issue of range.
It doesn't matter how much you spend on an antenna, the simple truth is that VHF radio waves are limited to a maximum range of line of sight. Period.
Bu when you add in angle of transmission amplitude (rocking of the boat), your effective
transmitted line of sight can momentarily be pointed straight at the surrounding waves, for as much as 60% of your actual time of transmission. This is where the decibel amplitude of the antenna comes into play. (SEE IMAGE)
Obviiously, a 3db antenna gives you the widest local transmission, where your vessel movement makes the least difference. The 9db antenna gives you the best range, with the sacrifice of angle of transmission amplitude. 9db antennas are really designed for a fixed land antenna. The 6db is best for most private small craft, and the 3db is best for sailboats where the antenna is located at the masthead.
Good advice can be found at West Marine here.
http://www.westmarine.com/webapp/wcs...s#.UajjrJz4KVg
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury