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Electronics

Controlling Power

Twenty-first-century technology has changed the way your electronics communicate.

It’s more than ten years now, since we learned to spell “millennium,” stocked up on canned food, and braced ourselves for the computerized apocalypse that was supposed to happen as we rolled over into the 21st Cen-tury—but never did. Yet while Y2K never lived up to its hype, one millennium project is, at last.

NMEA 2000 (or N2K, as it is sometimes known) is an internal communications system that distributes power and data to different pieces of electronic equipment around a boat. It allows a GPS, for instance, to send position information to a DSC radio and enables a chartplotter to display data supplied by an engine-management system.

Of course, the idea of sharing information between different pieces of equipment is hardly new: even in 2000, marine electronics had been communicating with each other for almost a quarter of a century. The first bash at the “industry standard” that made this possible was introduced by the National Marine Electronics Association (NMEA) in 1980, and by 1983 it had been through several revisions and one major rewrite that morphed it into the NMEA 0183 protocol. It says a lot for the success of NMEA 0183 that it is still the most widely used method of getting an instrument made by one manufacturer to communicate with one made by a different manufacturer.

But NMEA 2000 is far more than an updated version of NMEA 0183: it’s a ground-up redesign combining a communications protocol (CANbus) that has been thoroughly tested in the automotive industry with rugged cabling and connectors (DeviceNet) that were originally designed for use in automated industrial equipment. Consequently it has plenty of advantages over its predecessor:

  • In N2K, the cables and connectors that carry data from one instrument to another also carry power—not a lot of power, it’s true, but enough for most electronics, apart from radars and autopilot drives.
  • In NMEA 0183, each “talker” instrument can send data to just a handful of “listener” devices. With no standard color-coding or terminology, connecting each talker to the right listeners can be a lengthy process in which mistakes are easily made and time-consuming to rectify. N2K, on the other hand, allows up to 50 different devices to communicate with each other via simple plug-in connections and standard color-coded wires.
  • Brand-specific names such as Simrad’s “SimNet” and Raymarine’s “SeaTalk NG” tend to conceal the fact that the marine electronics industry in general is enthusiastic about the “new” system: SimNet and SeaTalk are both essentially N2K systems using identical data messages, the same signal voltage, and very similar five-core cables. The most obvious difference—and the reason these protocols are described as NMEA 2000 “compatible” rather than “compliant”—is that they use different plugs.

    But allowing navigation instruments to talk to each other, or getting engine data to appear on a chartplotter screen, is just the beginning. Simrad, for instance, has just announced an upgrade to its NSE series of multifunction displays. As well as adding autopilot controls and the high-frequency, high-definition Structurescan sonar, the new version is now compatible with Marinco’s C-Zone digital-switching system. Why is this important?

    Conventional electrical systems use very heavy cable to carry power from the boat’s batteries to a distribution panel or main circuit breaker panel, then use slightly lighter cables to distribute power from the panel to each individual switch and appliance around the boat. This works well on smaller vessels, but as their size and sophistication increase, this type of system becomes more and more expensive to install, and the sheer weight of copper wiring involved becomes significant. In a distributed electrical system, each part of the boat—the engine room, galley, accommodations, wheelhouse, and so on—has its own individual distribution board. In C-Zone’s version of a distributed system (shown here) conventional circuit breaker panels are replaced by electronic output modules using digital switches instead of circuit breakers, backed up by good old-fashioned fuses to provide ultimate protection in case any of the digital switches fail.

    A distributed system also brings big savings in installation time and in the weight of copper involved. And digital switching brings a host of new benefits including the possibility of alarm systems that warn of low current, like those caused by the failure of a navigation light bulb, or high current, such as might be caused by a clogged pump. These systems can be programmed to switch off unnecessary loads if battery voltage falls and can even incorporate dimmers and timers.

    By joining forces, Marinco and Simrad have taken another step: using NMEA 2000’s ability to transmit control messages as well as data, a boat’s entire electrical system can be monitored and controlled by a chartplotter! An NSE display can now display information like battery condition, charging current, and shore-power voltage, and it can show which circuits are in use and which are switched off. But it can also switch individual circuits on or off and be programmed so that a few keystrokes are all you need to switch from one operating mode to another—from underway to anchored, for instance, or from daytime to night.

    So while Y2K was a flop, N2K has been a success, making control of your electrical system much easier.

This article originally appeared in the May 2010 issue of Power & Motoryacht magazine.

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