A few things I have found to be of a great help when doing wifi and voip..
1. Get the strongest flat panel or directional antenna you can get, with the highest dB rating. Ask Richard or Susan over at AntennasDirect (.com) for their advice. They have some excellent models for sale there. A flat panel will work a little better if you are in rocky waters.
2. Get the router with the highest amplification possible, such as the new D-Link DWL-7200AP (see dlink (.com) wireless networking). Choose a model though that will allow you to connect your external antenna with adapter.
3. Keep your router as close to the antenna as possible so that your wire run will be much shorter. Quad-shield RG6 is best if you can terminate it yourself (see your local radio shack).
4. Setting up a repeater [not needed] for your (stolen) wifi signal will allow you to rebroadcast that acquired signal with an omni antenna to all the boats in your area.. maybe even charge your neighbors a little fee and setup mac address filtering on the repeater.. hehe
5. Skype is absolutely fantastic. I use Skype exclusively for my phone. It is internet based, so your free wifi service will work great for this. Your laptop computer becomes your phone. If your stolen internet signal out on the boat isn't giving you enough bandwidth, then Skype also sells little handheld wifi phones now for under $200: (skype (.com)) Just take the handheld wifi phone into the closest wifi hotspot or cyber-cafe and use it like it was a cellphone. Great sound quality with skype too.
6. The stronger your antenna, and the stronger the amplifier is in your router, the more reliable your wifi/internet signal will be, and the better your chance will be for greater bandwidth (download/upload stuff a lot faster, watch movies online, broadcast video from your webcam, etc)..
Kind of off topic here, but I found a company called Rick's Satellite that sells satellite systems that will get you free HD tv/radio signals too (google: gofastmotorsports rickssatellitehome). I have his home system, but I think he has marine systems as well.
Hope this helps