NMEA2000 Networks

Back in the mid 80s Bosch developed the CAN bus, or Controller Area Network Bus to allow all the electronics on a modern car to talk to each other. In this case, a bus isn't a big long car with wheels, it's a type of network where all devices on the network share information such as the ethernet network in a home or office.

NMEA networks are a standard developed by the National Marine Electronics Association that is electrically compatible with CAN bus developed by Bosch for cars. The first version of NMEA was NMEA0180 which was a single talker multiple listener network. The current standard for boats is NMEA 2000 (sometimes abbreviated to NMEA2k or N2K) but there is also a legacy NMEA0183 standard that is slowly being phased out (in recreational boating at least.)

To understand why such a network is a good thing, let's go back and look at the way things used to be. Originally Renko had a radar, GPS, radio and depth sounder in the wheelhouse, none of which could talk to each other.

The next step in the evolution of this technology was to have a multifunction display where each sensor is plugged directly into the display. By sensor I mean a sonar transducer or a radar transceiver. This allows features such as radar information being overlayed on top of a chart, but still means that the MFD is at the hub of all communications.

Similar to the way your printer used to need to be connected directly to your computer's USB port but can now be on your home network and shared by all computers, NMEA allows marine devices to be shared in a similar way.

Renko has a SeaTalk NG network which is electrically compatible with NMEA2000. NMEA2000 is a bus network which means that no one device is at the centre of the network and all information is broadcast for all devices to receive. This means you can have multiple displays in multiple locations, devices can continue to operate even when all the multifunction displays are turned off. An example of this is that the P70 autopilot control head can direct the Evolution course computer which can in turn control the ACU200 Actuator Control Unit to turn the rudder all while the main MFD is turned off. As another example, if I send an emergency distress signal from the Ray63 VHF radio it can fetch my location from one of 4 different sources of GPS information broadcasting on the NMEA network. As you can see, this gives a huge amount of flexibility and redundancy.

Rather than the standard Micro-C connectors, a Raymarine SeaTalk NG network uses proprietary connectors that are both marinised (o-ring seals), colour coded for easy installation and smaller diameter for easier running through conduits etc. Cables with Micro-C on one end and Raymarine connectors on the other are readily available.

To make things a little bit more complicated, Renko currently has two networks, an NMEA (STNG) network for low data devices and a RayNet network which is essentially a marinised ethernet network for both regular computing and high-bandwidth devices such as cameras and radar.

The next generation of NMEA networks aims to bring these two together and is unsurprisingly called NMEA OneNet. This will bring the bandwidth required for all modern marine instruments and sensors as well as internet connected computers onto a single network.

It's also worth noting that NMEA networks are capable of powering low-current devices from the NMEA backbone itself. One such device is my P70 autopilot control head. These devices are rated in LEN (Load Equivalency Number) where 1 LEN equals 50mA. The P70 is a LEN 3 device so it draws 150mA.

Finally, NMEA isn't just for big boats! Most larger modern outboards are also designed to send data to an NMEA network so that information like temperature, RPM etc can be monitored and displayed anywhere.