Port 8375
Deltas sent over tcp must be entirely on one line, and terminated by \r\n. (What happens if there is a solitary \n or \r in there?)
Seems to be it's preferred transport. Port as configured web interface, default 3000, maybe 80 / 443.
TCP port 10110.
It can use a SocketCAN adapter, e.g. CANable/candlelight as follows;
NMEA 2000 Source: Canbus (canboatjs)
Interface: can0
See also: CAN Interfaces
Recently OpenCPN has added SignalK support. It will connect to a SignalK server using the websockets protocol on (default) port 3000. You might still need to build from source to get a version that supports it.
SignalK has pretensions to being a reïmplementable standard, and so has two sets of documentation.
N.B. The specification is not entirely implemented in the server, and the server docs don't tell what doesn't conform.