Into the Nitty-Gritty of NMEA 2000
The N2K data-sharing standard can improve your electronics network, but don't dive in without some knowledge of cable and power details. An electronics review from our July 2009 issue
Courtesy of Ben Ellison
|Stripped back cable from Maretron (above, left) and Raymarine reveal similarities: White and blue wires carry data; red and black wires are for power.|
For some of us more elderly sailors, just getting a wind gauge in the cockpit was a big deal; reasonably accurate at-a-glance apparent-wind direction and speed was a significant upgrade from neck-wrecking Windex pointers and overrated ear-lobe anemometers. But a sailboat skipper really wants wind data everywhere. What if your boat could have as many different wind displays-dials and/or graphics-as the crew could possibly need for trimming perfection, a wind rose overlaid around the helm plotter's boat icon for situational awareness, and the same data delivered to, say, the performance software the offwatch likes to fool with on the nav station computer?
And what if the masthead wind sensor easily networked with the GPS, a knotmeter, and heading sensors so you could select among readings for apparent, true (relative to boat), and ground (relative to Earth) wind on any of those displays? And finally, what if the various components of this system could be sourced from multiple manufacturers according to your personal criteria, be they accuracy, style, durability, or price?
That's the promise of the National Marine Electronics Association's 2000 data-sharing standard, and I'm here to tell you that it makes all of the above quite possible, and more. NMEA 2000-compliant sensors and displays can share not just such familiar data messages as wind, depth, and go-to waypoint, for example, but also a growing list of more esoteric items, including fuel-flow rate, bilge-alarm status, and system-control commands.
Moreover, the standardized N2K plugs and cables containing the wire pair on which all this data travels also contain power wires bearing enough juice to run many types of sensors and some power-efficient instrument displays, further simplifying a boat's wiring. And finally, various strategies are emerging that enable older electronics that use the original NMEA 0183 standard or such offshoots as Raymarine SeaTalkNG to marry a NMEA 2000 network, thus allowing a boat to evolve into the new standard.
Ah, but of course: There are confusions and complications. Many of the very manufacturers that worked together to develop the 2000 standard a decade ago appeared to get cold feet as it was actually introduced. My guess is that the original marketing premise-to make the then-prevalent mixed-brand "best of breed" helm concept work better-got torpedoed when new multifunction displays proved that one brand alone could own the whole helm. At any rate, some companies were slow to adopt N2K, while others used loopholes in the standard to create N2K variants obviously meant more to integrate their own devices than to plug-and-play well with competitors.
It really wasn't until 2008 that NMEA 2000 became the dominant way to pass around succinct data messages. (Radar, sonar, and video are too verbose to use N2K, and while Ethernet is often the cabling employed, the overall connections remain proprietary.) So while most new multifunction displays, autopilots, instruments, and sensors support N2K, many of the folks who sell and install them are still inexperienced with the nitty-gritty. Which is one good reason why it behooves sailors contemplating new or updated electronics to learn some N2K details, even if they don't intend to undertake their own installation-although in many cases, N2K makes that easier than ever.
Consider the weird profusion of available N2K cables. The NMEA itself based its plug and cable specification on an existing industrial standard called DeviceNet, specifically its Mini and Micro sizes. While garden-hose-thick Mini is more suitable for ships and megayachts, even Micro is waterproof, heavily shielded from electromagnetic interference, and very tough. Nonetheless, Raymarine and Simrad each designed its own proprietary cable system, SeaTalkNG and SimNet respectively, and some companies, including Garmin and Lowrance, came up with lighter Micro clones. The latter are plug-compatible with Micro, but their plugs are plastic, not metal, and none of these cables seem to offer Micro's level of shielding and ruggedness.