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NMEA 0183, NMEA 2000, or Ethernet?

NMEA 0183, NMEA 2000 or Ethernet?

We live in an era where chartplotters, echo sounders, radars, instrumentation systems, audio-visuals inputs, engine data feeds and many other sources of on-board information can be interconnected to exchange, process and display each other’s data.  It can therefore aid the decision-making process to understand the different ways that data can travel between the various units in what is generally described as an integrated navigation system.   There are three standards currently used in the leisure marine sector:

NMEA 0183

NMEA stands for National Marine Electronics Association (of the USA).  NMEA 0183 was first introduced in 1983 as a voluntary industry standard for data communications among shipboard electronic devices.  It uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one ‘talker’ to one or more ‘listeners’ at a time, and therefore cannot be used to create networks.   Data transmission is slow by today’s standard at 4800 bits / second and the standard does not allow for multiple ‘talkers’.  However it is still in widespread use and is perfectly adequate for situations where one piece of equipment, for example a hand-held GPS, is to be connected to another such as an on-board chartplotter where the user wishes to integrate the two sets of data.

Generally, however, NMEA 0183 has been superseded by the NMEA 2000 networking standard, although many devices are designed to communicate using either standard.

NMEA 2000

Currently the accepted standard across the international marine industry, NMEA 2000 is much more sophisticated than NMEA 0183 in that it allows multiple units to simultaneously both transmit and receive data.  With the inclusion of multifunction displays into a networked system the user can then choose any combination of data outputs to be displayed at any position or for any situation.  It is NMEA 2000 that has made possible the development of the integrated navigation and control systems that are now being fitted on craft of almost every size and application.

NMEA 2000 has a range of advantages over its precursor, NMEA 0183.  The cables carry the current as well as the data, reducing both the cabling requirement and the risk of electromagnetic interference.  Devices are connected using CAN (controller area network) technology and NMEA 2000 not only allows the transmission of data at vastly great speeds than NMEA 0183 (250,000 bits / second versus 4,800 b/s), but also in a more compact form, making it far more suitable for complex, multi-unit systems.  Navico’s SimNet networking system uses NMEA 2000 protocols.

Finally, as a common standard NMEA 2000 allows the boat owner to interconnect equipment from different manufacturers.

Ethernet

Ethernet is a widely-used cable-based technology for transmitting very large amounts of electronic data between units of equipment within a LAN (local area network) and as such can be found in all forms of computing technology across every aspect of modern life.

Capable of transmitting at rates of 10 MB per second and more (versus 0.25 MB p/s for NMEA 2000) it can play a valuable role with marine electronics that process high volumes of data, for example radar, electronic charts and weather overlay information, and it is now common to find such units that now offer both Ethernet and NMEA 2000 connectivity.  However there is no marine standard for Ethernet and equipment from different manufacturers may not be able to communicate with each other.  In addition, unlike NMEA 2000 it does not have the ability to prioritise the transmission of critical data and so is not recommended for applications such as steering or throttle that require a near-instant response.

Summary

All three technologies continue to play important roles in the inter-connecting of marine electronic devices, and users are advised that they discuss their requirements with their dealer before determining which is most suitable for their particular needs.

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