I just bought (and returned) a Radio Labs RVWave usb wifi adapter and
antenna. It didn't work any better (or worse) than the wifi card built into
my laptop. It (and my laptop card) would only give me about 200 feet usable
range from my home wifi router. Other users reported similar results on
Panbo. Out of 3 or 4 posters only one said it worked.

The Engenius system looks nice, but requires 110V ac for the Ethernet DC
injector. It works on 48 V DC, so DC power is not an option on my boat.

I am leaning to a system assembled by a cruiser from commercial parts. See
www.islandtimepc.com. Bob Stewart builds these using an Ubiquiti
Litestation2 board. It is powered by 12V DC injected into the Ethernet cable
and is a 400 mw amplifier. The amplifier specs indicate good sensitivity.
Bob sells a package with cables, POE injector, the Ubiquiti board mounted in
a waterproof NMEA aluminum box and an 8 dB antenna for $329. Skip Grundlach
a cruiser on this board swears by the system.

David