choose UDP ports

[Techstyle]

In fact I want to route the position (RMC) to a VHF (NMEA interface), and the pilot control (APB, XTE) to a Pilot NMEA interface.

1st in opencpn, I created 2 outgoing UDP connections with the proper sentences : OUT1 to Pilot, UDP 10116, and OUT 2 to VHF, UDP 10118 ;

In the in nmea0183-to-nmea0183 plugin I also selected the proper NMEA sentences attached to 2 newly created output events (for both pilot and VHF ) ;

Then in Signal K, I created 2 connections : to the UDP 10116 to (the RS422 USB device linking) the Pilots' output event, and to UDP 10118 to the  RS422 USB device linking the) VHF's output event 's ;

I selected the port numbers (10116 & 10118) with a blindfold,   and by pure luck it is working, so far !

I would feel much more relax if a skilled person could bless this choice (in UDP port numbers) or adversely advise me which numbers should I use !

Firstly, RMC should come from your GPS device to OCPN through the existing, incoming to OCPN connection. which should look something like below:
   

then setup the outgoing connection from OCPN, notice I only send XTE, APB, RMB - this stops message loops.  your 10116 or 10118 should be fine, but you don't need separate outputs
   

On the Signal K side, add a data connection (Server => Data Connections) per below, make sure the port is whatever you use:
   

now you will have all the data in signal K and be able to see it on the Signal K data browser. 

after that, you can send the sentences out by setting them in SignalK to NMEA0183 plugin and a serial connection to your VHF and AP (which I think you already have)