Connect your plotter directly to NMEA2000, it doesn't understand Signal K (yet!)
The iKommunicate will translate NMEA0183 and NMEA2000 to Signal K. Additionally it will output your NMEA0183 inputs as well as the NMEA2000 inputs over Ethernet on port 2000, see the admin page.
There are a number of Signal K ready apps, but OpenCPN
is not one of them. I know that there are plans for OpenCPN to support Signal K directly, but for now that is not implemented yet and I don't know when Pavel will be able to add this. Certainly not before 5.0, maybe later. So for now you'll have to use the NMEA0183 conversion done by the iK.