If you're on a boat all your devices probably have NMEA (RS485) phoenix connectors on the back for the "A" & "B" RS485 signals.
If you use MAX485 chips you might be able to connect them that way but you need to know about "talkers" & "listeners" and what the "talkers" are saying and what the "listeneners " are listening for. (all of which is in their manuals)