SV Tashmoo wifi system.
We have tried many different wifi antennas or configurations aboard Tashmoo. Including both directional and omni-directional. The directional antennas work okay but not on a swinging boat at anchor. The best system we have found was made up of the following three components:
1) HG2415U-PRO HyperGain® 2.4 GHz 15 dBi Professional Omni Antenna $99.95
2) CA4NMRSF030 Custom Cable Assembly, N-Male to Reverse Polarity SMA-Plug (Female) 400-Series 30 ft $44.99
3) EnGenius EUB-362 EXT $44.00
I purchased the antenna and cable from www.HyperLinkTech.com. You want a high gain antenna and a good cable. Cheap cables will add loss. I don't remember where I purchased the EnGenius from but if you do a goggle search on the part number I'm sure you'll find several places selling the unit.
I've mounted our antenna ~10 feet above the water on our arch and it is not unusual that we have wifi several miles offshore. This system also does not require any external power to be supplied. It only requires one USB connection. The cable listed above is 30' long, which is what Tashmoo required. Other lengths are available from HyperLinkTech. We've compared our wifi to many other boats and haven’t found one that works much better and is so simple.