Thanks to all for the replies and I will go through the suggestions. First to clear up what I have done:
1. I have a setup on the boat and I am using a simple setup at home to test the further development.
2. On the boat I am using 2 RPis :
a: one is connected via usb/RS232 to a SeaTalk
converter, a GPS/AIS, and a wind
instrument; it runs KPLEX and successfully outputs through wifi
and an ethernet cable to the chartplotter
b: the second RPi is the chartplotter
sitting inside an HDMIPI screen
and receiving data from the first RPi through eth0; it works well and OpenCPN correctly receives data
c: I can receive nmea on Android tablet and run mobile OpenCPN on that
3. at home I have 2 RPi connected by ethernet cable. I have inputs from a GPS
dongle (with view of the sky) and from barometer, temperature, and humidity sensors.
4. I can successfully ping both ways between the RPis
5. I can run KPLEX on each RPi and send GPS
or sensor messages both ways, combine them and send them back. I have tested with GPS on one RPi and sensors on the other and with both on one.Thus my basic communications
setup seems to work OK
6. I am trying to prepare for outputting autopilot messages on the boat and replicating it at home. I have OpenCPN running on one RPi and KPLEX on the other with GPS and sensor inputs. Open CPN
runs fine and receives all data and filters as required. I have set up separate outputs on OpenCPN trying TCP, UDP, and FIFO file. The output works fine for retransmitting incoming sentences such as GPRMC but when I activate a route it does not send EC messages.
7. I also have a receive TCP or UDP on the KPLEX RPi and this only shows the retransmitted data (rapid loops can be developed. Very occasionally I see EC messages on the KPLEX machine but this is mainly when I am shutting something down.
8. Both RPi are v2 and run at less than maximum capacity.