So that's communication over 8 nautical miles, or 15 km, presumably line-of-sight. Consumer equipment (5 GHz wimax ac) can do that with a 20x20 cm directional antenna. Have a look at a Ubiquiti NanoStation, for instance. Sticking up a pole with a 20x20 cm fiberglass antenna on it won't give a radar return distinguishable from wave noise even at calm seas.