Article by Capt. Steve Katz
What is NMEA2000?
This week, we will review a technical aspect of marine electronics - data communications between hardware on-board our boats. Just as we like to share information and talk to other people, our marine electronics have for years had the capability of doing the same thing.
The National Marine Electronics Association (NMEA), founded in 1957, is the trade organization that brought us popular standards such as NMEA0183 and NMEA2000.
The NMEA0183 standard was published in 1983 to allow marine electronics to talk and listen to each other using a standardized communication protocol. Updated many times since its inception, the NMEA0183 standard is still in use today. NMEA0183 is a serial data interface that allows one talker and multiple listeners. For example, a GPS is the talker and the VHF radio is the listener and maybe the depth sounder or autopilot also. This standard allowed marine electronics from different manufacturers to share data, allowing helpful integration of the navigation electronics at the helm of the boat. The physical connection between the devices is not standardized by color or connection. Generally a two wire conductor is used to connect the devices together and wires are identified by transmit and receive depending on the function.
In the middle 1990's NMEA members and other industries leaders (over 40 organizations) started to develop a more robust data protocol that would be able to expand with the capabilities of the current and future marine electronics. The first NMEA2000 standard was published in 2001. This standard is based on Controller Area Network (CAN) technology which shares some similarities with the auto industry's J1939 standard.
The NEMA2000 standard is a complete standard, with specifications for connectors, wires, power and data format. NMEA2000 is 50 times faster than NMEA 0183 and can have multiple talkers and multiple listeners at the same time. It also doesn’t require a master controller or device on the network.
NMEA2000 is sometimes advertised as a plug and play system due to the fact that the NMEA2000 certification means the product has been tested by NMEA and is capable of being used in a properly configured network with no known issues. This means you should be able to go out and buy any manufacturers marine electronic device and it should talk and listen nicely with the other NEMA2000 hardware on your network. Since the connectors are all the same, all one needs to do is plug in that new device to your existing network and it should work.
This may be a good place to break from the technical aspect and talk about the benefits.
Here is a real world example - You have a 5-year old 4212 Garmin chartplotter on your boat with an existing NMEA2000 network connecting your GPS antenna to the chartplotter. At the boat show you see the new ICOM M506 VHF radio that has built-in AIS (Automatic Identification System). You buy and install the new ICOM VHF radio and using a standard NMEA drop cable and tee, connect the ICOM to the Garmin through the NMEA backbone. This allows the Garmin to tell the ICOM your latitude and longitude for DSC while at the same time the ICOM can tell the Garmin chartplotter about the AIS vessels in your area and draw them on the Garmin display. This is a practical example of different brands and ages of hardware all sharing data back and forth.
So how do you get started with NMEA2000? The good news is that you might already have it! Manufacturers such as Garmin, Furuno, Simrad, Lowrance and Raymarine have all used NMEA 2000 standards in their hardware or brand specific connectors, such as Simnet, (that can be adapted to NMEA2000). If you do not already have a NMEA2000 network, it can be set up rather easily with the numerous technical publications and instructions from major manufacturers.
The NMEA200 network is comprised of a backbone cable (think of it as a tree trunk) and drop cables to each device (think of it as a tree branch). The backbone transports the data from end to end, sharing it with each network drop along the way. A backbone, using standard NMEA2000 cable, can be no longer that 100 meters (328 feet) and each network drop can be no longer than 6 meters or about 20 feet. So now that we have a backbone and drops, we need a few more pieces of hardware to complete this network. We need electrical power, 9-15 volts DC, properly fused and connected to the backbone using a tee. We also need network terminators (120 ohm resistors), one on each end of the network. Now that a proper backbone is set-up, all you will need to do is install tees and drop cables to connect each NMEA2000 certified device to the network. This can be done when the network is powered on, it is not necessary to shut down the network to add or remove devices. Remember you can only have one device per drop You CANNOT daisy-chain devices.
Once your hardware is connected, there may be some minor configuration needed, but for the most part, the devices will automatically begin to transmit and receive data instantly.
There are some private communications that move across the NMEA2000 network that is not available to all devices. A popular example is Garmin's Autoguidance, where the Garmin chartplotter designs a route for you and only a Garmin autopilot can use that data on the network. A Simrad autopilot can not follow the Garmin Autoguidance data, but a Simrad autopilot can follow a regular waypoint course or route broadcast on NMEA2000.
There are many, many NMEA2000 devices being designed everyday for almost any application, such as engine data, multifunction screens, weather stations, stereo controls, electronic switching, tank level gauges and flow meters.
The NMEA2000 standard will allow you to easily expand and compliment your marine electronics system when and how you like with the ease of plug-and-play technology.
Captain Steve Katz is the owner of Steve's Marine Service and holds NMEA MEI, AMEI, NMEA2000 certificates, ABYC Master Technician certification and factory training from many manufacturers.
