I understand Cat5 as a "normal" IP/Ethernet wired network. (For me Cat5 is the technical capabilities for the cable hardware
and not what kind of data is sent trough that cable.)
As long your PC can connect to the IP-network OCPN can read and send data. So it's all about what your MFD's are sending. OCPN can interpret most NMEA 0183
messages but not NMEA 2000
. Most makers, like Raymarine
, use a data bus either called something cryptic or just NMEA 2000
(2k) and seldom transmit using the NMEA 0183
protocol. There are a couple of soft- and hard-ware converting from 2000 to 0183 but you've to be more specific about your needs.