Sitting in Gulf Harbour just now..... stern mounted AIS
Ant ( base of which is 1.7 metres above sea...not on a 'roll bar')..... happily picking up Class B signals from harbour ferries down at Bucklands Beach 16.1 miles away. This isn't 'line of sight' as Rangitoto Island -which is no small thing -lies between here and there. Ant height on the ferries is maybe 6 or 7 metres.
Thats them down lower right.....
The ferries here all run Class B and typically poke along at 20 knots..... HMNZS Wellington is also running Class B... don't know about the rest of the NZ navy
and also... that's the display software
that came with my AMEC.