Marine Technology Notes: Plug and play for boat networks

For years the National Marine Electronics Association has had a standard method for interfacing electronic devices. Called NMEA 0183, it allowed a GPS from one company to exchange data with the autopilot of another company. As a standard, however, 0183 had some problems, not the least of which was that sometimes it lacked, well, standardization. Not every manufacturer used this interfacing language in perfect lockstep.

The shortcomings of 0183 have long been known to the technical people at NMEA. So for some time, this industry group worked on an improved technology. Called NMEA 2000, this latest networking standard is a big improvement over 0183, giving boat owners added power and flexibility to move data around a boat’s onboard network.

Although many voyagers may not have heard of it, the NMEA 2000 standard was released to manufacturers and the public a few years ago. “It’s a fully functional and released standard,” said Larry Anderson, NMEA standards committee chairman. Acceptance by manufacturers and the public has been slow, however. According to Anderson, only five products had been certified by NMEA as of early September. The standard may be picking up steam, however, as Anderson noted, “Within the next two to three months there are 30 to 40 products in process to be certified. A few companies are working on families of products.”

Most boat owners with an investment in 0183-based products won’t be ready to switch over to NMEA 2000 right away, but they will undoubtedly be interested in the advantages the new standard provides when the time comes for new instruments and a new network on their boat.

Unlike the 0183 standard, which is a general framework for simply exchanging data (and a loose one at that) and which doesn’t have rules concerning how data will be exchanged on a network or what type of networking hardware is acceptable, the NMEA 2000 standard specifies not only the format for data, but how it will shuttle around on the network and also what networking hardware can be used.

The 0183 system uses “point-to-point connections, with each unit needing to be wired to each other,” Anderson said. NMEA 2000, by contrast, is a modular network into which components can be plugged and unplugged without affecting the operation of the whole. NMEA 2000 uses a backbone cable, which can be up to 656 feet (200 meters) long with T-connectors that allow up to 200 individual components to be connected and disconnected from the backbone at up to a total of 50 nodes. Like the FireWire (also known as IEEE 1394 and i.Link) networking technology used in the computer world, NMEA 2000 carries its own power, so low-power devices can be powered from the network. Devices that use more than one amp when operating need to be powered from an external source.

NMEA 2000 is based on CANbus (certainly better than CAN’T bus) technology. The acronym CAN stands for controller area network. This means that unlike a system that uses a central controller to run a network, in this system each device contains a CANbus chip with the full instruction set, allowing each instrument to be a full-fledged citizen of the network and eliminating the need for a centralized brain and “traffic cop” to route signals.

The CANbus system used by NMEA 2000 was originally invented by Bosch in Germany as a network standard for cars. When Frank Cassidy of NMEA — Anderson’s predecessor at the standards committee post — was looking for a system to replace 0183, he chose the Bosch-derived CANbus system. In addition to the advantage of using a network system that was already developed for vehicle use and only needed some minor modifications for marine work, the NMEA could also count on the fact that large numbers of autos are built each year, and thus, networking parts (the cable and connectors) for the NMEA 2000 system are readily available and relatively inexpensive. In addition, the CANbus chipsets are made by a variety of microchip manufacturers, like Motorola, NEC, Siemens and Phillips.

Of course, if you are looking for a networking system even more widely used, the answer would have to be Ethernet, the networking technology commonly found in offices and in homes. The NMEA standards committee did look at basing the successor to the 0183 standard on Ethernet, which can easily transmit data in the 10-megabit-per-second range compared to CANbus’ relatively sedate 250 kilobits per second. But the committee decided against it since Ethernet-based systems have higher electrical power needs than a CANbus system. “CAN is a type of Ethernet, but it doesn’t have the power requirements,” Anderson said. “We have a strong eye to cost (when choosing a system). And we didn’t want to drive up the cost, especially for small boats.”

According to Scott Kern, chief software manager at Teleflex Morse, another reason for choosing CANbus over Ethernet was to ensure critical data arrived on time. NMEA 2000 is designed to prioritize data, so for example, data from an electronic throttle control will take priority over water-temperature data. On an Ethernet network, data flies around in more of a free for all, resulting in “data collisions” that require data to be re-sent. “With NMEA 2000, mission-critical data always gets there,” Kern said.

Because of its limited bandwidth, an NMEA 2000 network can’t be used to move around video, radar or electronic chart images. However, that is where proprietary high-speed systems like Furuno’s Ethernet-based NavNet and Raymarine’s HSB network can be used in conjunction with NMEA 2000 to handle data-heavy applications.

As noted above, one of the drawbacks of the older NMEA 0183 standard was the sometimes nonstandard way various manufacturers applied it. NMEA has made an effort to avoid those types of inconsistencies by requiring all manufacturers who wish to use the standard to submit their products for certification by the NMEA. The certification process is designed to make certain that all products on an NMEA 2000 network operate according to certain hardware and software requirements. Or as Anderson put it, to ensure “all the data that plays in the game of 2000 can be sent over the network.”

Even though NMEA 2000 offers plug-and-play capability as well as a slew of other attractive features, acceptance by the industry and the boating public has not been rapid. “It’s true that NMEA 2000 has been slow to be accepted by marine electronics companies,” Anderson said. “But as someone with experience in putting together engineering solutions, I know that these changes tend to be slow.”

One company that has embraced NMEA 2000 is Teleflex Morse, which offers a fully compatible NMEA network called MagicBus, along with a variety of instruments and controls. “We started five or six years ago and looked at where the next-generation boat would go,” said Teleflex’s Kern. “We were struck by the idea of an open architecture standard. As we progressed, we became more and more convinced it was the right solution. We feel this architecture has the best chance of being around down the road.”

By Ocean Navigator