Interfacing with NMEA 2000

NMEA 2000 is a newer version of NMEA 0183 with higher speed and better electrical connections it is electrically compatible with the CAN-bus developed for automobiles by Bosch in Germany .

There are different CAN-bus to USB converters available. With a simple converter the Raspberry Pi can be interfaced to the NMEA 2000 network onboard. 
Converters can be found several places, one example is (isolated) : USB-CAN USB to CAN Bus Converter Adapter. These controllers uses a chip that bridges between USB and a range of other interfaces, more here at FTDI. It's important to keep both +12V and service power GND isolated from the low voltage and sensitive computer system, hence the focus on isolation between the CAN bus (NMEA 2000) and the computer system.