Being a geek I tend to put 15 dBi gain antennas on the research
vessels I work with. These feed LMR400, LMR600 or LMR900 coax depending on the cable run.
I've not seen many problems with the beamwidth of the 15 dBi antennas. But then again big ships don't heel too much generally. And, on my sailboat I typically only use wifi
. No need to make the antenna
too high for a mile or so. Just 8 feet off the water
could be all that is needed.
Hyperlink technologies (L-com) has a good selection of antennas, cable and pigtails (to match you wifi card)
The max power (ERP) in the US is 4 watts. That is a 6 dB antenna
and a 1 watt transmitter, 9 dB antenna and a 500 mW transmitter or a 12 dB antenna and 250 mW transmatter or 125 mW and a 15 dB antenna.
You can actually fudge these figures a bit when you take into account cable losses but for the most part that is splitting hair.