NMEA 2000 basics June 7, 2010

Posted by Aquatronics Marine Electronics in NMEA 2000.
Tags: Maretron, NMEA0183, NMEA2000, SeatalkNG, Simnet
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This article is about NMEA2000 basics for integration into the new generation of marine instruments.

The idea behind this is to give you a basic understanding of what will be required to start a NMEA2000 instrumentation system. In future articles I will add ideas for expanding your system, integrating across different manufacturers systems and integration with your existing NMEA0183 products.

A New Standard

This new standard is now followed by most leading marine electronics equipment manufacturers around the world. Some of them having their own name for basically the same thing. Raymarine have the  “SeaTalkNG” network , Simrad use  “Simnet” and Lowrance Net,  products being part of the Navico group. Both  Garmin and Furuno and others have generally opted to use NMEA2000.  A relative newcomer to the marine electronics market, Maretron have been at the forefront of allot of high quality NMEA2000 products.

I have used the Maretron WS100 solid state wind sensor with Raymarine ST70 and E series displays with great success.

NMEA2000 is the new standard to replace NMEA0183 which has been around for a long time. The NMEA0183 standard has been useful if not at times very frustrating when trying to link several pieces of equipment together.

The NMEA2000 standard has gone some way to addressing the above problems. The standard is derived from the automotive world who developed the  J1939 standard.

Unlike 0183 There are 2 elements to the 2000 standard. A physical and electrical characteristic and a programming or data exchange component. The new format will transmit data at a much higher speed than the old system so the cable and connectors are an important part of the overall system components.

Setting up a NMEA2000 system.

Unlike 0183 the NMEA2000 system relies on providing a data bus or “backbone” for the system. This Back bone is essentially a long cable from one end of the boat to the other (possibly stating at the top of the mast) with a “termination”  at each end and a power source in the middle. All the senders and receivers are then “hung” of this line. The maximum length for the data bus (back bone) is 300 meters. The power must be injected about the mid point ( if the run is long). and the maximum spur length is 6 meters.

The terminators are important and will cause system failures if not working or have been removed.

As you can read from this there is a bit more design work required “up front” than a conventional 0183 system but it is possible to expand and modify a basic system if you have the back bone laid out.

Here is a basic system one might expect to construct. As part of the specification involves waterproof connectors – all connections are made using “spurs” . Do not cut and connect as you would have done with NMEA0183 cabling (there are field installable DeviceNet connectors for this use).

This drawing shows the back bone (highlighted in green) with the power inserted at the mid point.

I found this useful article from Panbo about the use of field installable  connectors.

NEMA 2000 issues

One of the main issues is that each manufacturer has their own proprietary sentences and this can cause some problems with interconnecting communications. You may find that some controllers will not able able to program the features or calibrate  senders made by other suppliers even though they can display the data. As well as this some suppliers will only display some of the data. This can be frustrating and it is therefore worth while careful consideration when mixing and matching products from different manufacturers.

Further information and products