[Gabriel] put together an impressive writeup of his autonomous catamaran, Atlantis(PDF). It was certainly done as an academic project, but there's a thorough explanation of the math logic behind the control systems. The heart of the boat was a waterproofed Pentium laptop with a CAN bus parallel interface used to talk to everything on-board. Sensors included GPS, wind, hull speed and rudder angle. In case the site can't handle the load, I've mirrored the 1.4MB PDF here.