A guide to NMEA 2000® installations for yachts
Last updated: 19/10/2016
Who are the NMEA?
The NMEA (National Marine Electronics Association) is a ‘not for profit’ organisation based in the USA who aim to strengthen relationships between manufacturers in the marine industry and make it easier for marine electronics devices to share data with one another.
The first international interfacing standard released by the NMEA that is still in use and recognised today is NMEA 0183, originally released in 1983 and still being actively updated on a regular basis more than 30 years later. NMEA 2000 was the second international standard released by the NMEA in 2001, and over the past 10 years has become the primary standard used on leisure marine vessels. The NMEA OneNet® working group is developing a new standard (now in beta test phase) designed to work hand-in-hand with NMEA 2000 and allow its data to be shared safely over Ethernet.
How does NMEA 2000 work?
Marine electronic devices from various manufacturers that are all NMEA 2000 certified can be safely connected to one central cable running through all relevant areas, known as a backbone. The backbone can provide power to all low-powered devices (requiring less than 1 Amp) whilst sharing data among all of the devices on the network.
The NMEA chose the DeviceNet standard for its NMEA 2000 cables and connectors as it was a proven and robust standard already used by the agricultural, industrial and automotive industries. Connections are "plug and play" which makes it easy to build an NMEA 2000 network and connect devices from many different manufacturers due to the standardised wiring and connector system.
A great example of how this can help the user in real life is when a yacht engine’s fuel flow meter and fuel tank level sensor share their data with the chart plotter so it can calculate how long it will take to empty the fuel tank – add vessel speed as well and the ‘distance until empty’ can also be calculated. Another is when a yacht engine’s data can be monitored on MFDs anywhere throughout the vessel, not just at the helm with the help of analogue to digital converters like the Actisense Engine Monitoring Unit (EMU-1).
How to set up an NMEA 2000 network
The first part of any NMEA 2000 network installation must be to decide the route taken by the backbone cable. On a large yacht this could be made up of multiple cables connected in series running through the whole vessel, or at its simplest, just two T-pieces connected together.
Wherever there is a need to connect an NMEA 2000 device, a “T-piece” is inserted in to the backbone and a “Drop” cable used to connect the device to the T-piece. NMEA 2000 connectors are simple to connect to each other using threaded ends that screw together and device drop cables can be attached or removed from a T-piece without interrupting the network.
A drop cable should never exceed 6 metres in length and a real effort should be made to keep them as short as possible. Other limitations users should be aware of, as well as the different cable sizes that can be used for NMEA 2000 backbones, are listed in the table below.
<h2>NMEA 2000 cable specification</h2>
The backbone is powered via a “Power T-piece” or more advanced solutions such as the Actisense Quick Network Block (QNB-1). As the name suggests, this looks just like a regular T-piece used for device drops, except the middle connection is a long cable for connecting to a fused battery supply. Ideally the power T-piece should contain two power pairs so that it can be placed in the “power” middle of the backbone (with regards to electrical demand), with power distributed evenly to each half.
The backbone must be terminated at each end with a “Terminator”. Data corruption will occur if there is anything but two termination resistors per NMEA 2000 network.
The Actisense NMEA 2000 Starter Kit provides everything necessary to create a minimum NMEA 2000 network, making it an ideal way to start building your NMEA 2000 network. The complete Actisense A2K range provides networking solutions to help build an NMEA 2000 network as the demand for devices grows.
Problems with NMEA 2000 for yachts
The cornerstone of NMEA 2000 is extremely high reliability when sharing vital navigation data where reception of that data must be guaranteed. As Ethernet networks cannot guarantee data reception, the NMEA chose “CAN” (Controller Area Network) for NMEA 2000 because it guarantees reception of messages by all devices.
A benefit of that decision is that no “switches” are required to build a network, however it cannot transport video and other imagery signals that require a high-bandwidth connection. This results in Ethernet cabling being required on some yachts to transfer radar, sonar or video camera images in addition to the NMEA 2000 backbone cable. Looking forward, NMEA OneNet will bring these two networks together to form a hybrid network that has the capabilities of both.
Whilst NMEA 2000 is "plug and play" at the (cable and connector) physical level, networks that offer more than one data source of a particular type (for example, two GPS or depth sounder devices) require some device configuration to manage the increasing complexity. When networks grow further still, an NMEA-trained dealer or installer is recommended to help create a reliable network.
Benefits of NMEA 2000 for yachts
NMEA 2000 allows a yacht engineer, owner or captain to choose the best possible products from a wide range of manufacturers. They no longer need to stick to the same brand for every device, and as long as the electronics carry the NMEA Certified mark, all of the products will work together seamlessly.
Steve Spitzer, NMEA Technical Director has previously stated, “to date there are nearly 600 marine electronics products that carry the NMEA 2000 label, and more are being added all the time. You can see a comprehensive list by visiting NMEA.org.”
Diagnostic tools are available to help a user and/or installer understand an NMEA 2000 network, from a list of the devices, to the exact messages being sent around the network. “PC Gateways” (like the Actisense NGT-1) are invaluable when used with diagnostic software (such as the freely available NMEA Reader) to find the source of an issue and understand the actual data available on the network. They can also record this data to a “Log” file that can be shared with the Tech Support teams from a number of manufacturers.
Connecting NMEA 0183 and NMEA 2000 together
Many yachts and boats still have working NMEA 0183 marine instruments that the owner would like to be part of an NMEA 2000 network. Products known as “NMEA 2000 Gateways” (like the Actisense NGW-1) convert data from NMEA 0183 to NMEA 2000 (and vice versa) can be used with these NMEA 0183 devices to give them a new lease of life and allow their data to be shared on an NMEA 2000 network.
A typical real life use of an NMEA 2000 Gateway is to allow the vessel’s latitude and longitude (from an NMEA 2000 GPS) to be shared with an NMEA 0183 VHF radio so that it can send that data in case of an emergency distress call. Another is to allow an old-but-still-good NMEA 0183 depth sounder to share its depth data with an NMEA 2000 MFD or radar.