When I got my second nmea device, i was excited -- "hook it up" the manual said
-- support said "yes; you just hook up all the nmea out with nmea in of the
other devices and visa versa" so I did.

It appeared to work. however, since I have some weird things recently
discovered, we've traced it down to the fact that the info I got was wrong; and
my understanding of nmea was woefully weak.

GPS: listens & talks (2 lines of each)
RADAR: listens & talks
navtex: listens only
autopilot: listens only
flowscan: listens only
VHF listen/talk

Navtex, Autopilot & flowscan need to listen to the gps
radar & gps need to listen & talk to each other
The VHF radio talks/listens to the gps.

AIS receiver is in the budget & will need to talk to the gps & radar.

From a few hours search; it seems I need multiple-multiplexers to make this work
"correctly" -- can anyone give me a hand?

-josh