NavPilot511 doesn't have a network connection so you have to connect your NavPilot serial with your computer.
In MaxSea you will find in connection wizzard a point for autopilot connection.
It is a Little bit off-Topic but I own tha navpilot 711 and would like to connect this gizmo with maxsea. But it seems that maxsea only offers the Connection to the AP via Serial, not via LAN/Navnet??!!