I would avoid anything USB as the drivers are very flaky. I have tried several brands and none are stable. I would suggest the Ubiquiti products. this is a really old discussion, but there are a few that discuss teh NanoStation2. I use the NanoStation2loco it was under $50 and works really well, is weather proof, and is powered by power over ethernet, so there is only one wire leading to the antenna/radio unit. I went from a 1 megabit connection that was in and out to a full 54 megabit connection. It can run for weeks, and likely longer but I do a lot of torrents so that equals hundreds of connections and that seems to bother any wireless device. But for normal use I would imagine it would be stable for years without rebooting. I got mine here:
NanoStation loco - NanoStation loco 802.11B/G 8dbi CPE
No business connection, just a happy customer. Actually had the best customer service I have ever experience. They have a product called a bullit that allows more choice on the antenna, but you don't want anything to directional on a boat, as you are moving and your signal will go in and out with a very directional antenna.