Here Comes Class B

Thanks to Software Radio's all-in-one PCB, firms like Comar coan easily produce Class B AIS units-once they are approved.

That printed circuit board (PCB) at right may not look like much, but it's a key ingredient to the any-moment-now advent of Class B AIS transponders, and for that we kiss it. The evolving Automatic Identity System (AIS) has already revealed itself as a revolutionary improvement in marine safety. As I wrote here in January 2006, phase one was the mandated installation of Class A transponders on almost all large commercial vessels, which lets them "see" each other with more precision and detail than the most sophisticated radar (which they neatly complement). Phase two was the arrival of simple AIS receivers along with compatible charting programs and plotters that let us recreational boaters "see" the big guys, too. Now even that little 5.6-inch Northstar Explorer can deliver a wealth of information about nearby—possibly too nearby—ships.

AIS phase three will include low-cost, easy-to-install Class B transponders meant to allow smaller boats to actually participate in, not just monitor, the System. Now, ahem, I did write that Class B would arrive late in 2005 and "probably in the $2,000 range." Obviously I was wrong about the timing, but happily I also had the cost wrong. U.S. Coast Guard AIS regulatory project officer Jose Arroyo told me that two of the Class B units currently awaiting U.S. approvals will retail at around $900. He couldn't reveal brand names, but I'd bet that both contain the PCB above, which is a virtually complete, and economical, AIS transceiver created by an English company called Software Radio Technology. SRT, as it's known, was the first to pass Class B's hardware standard—Coast Guard and FCC approvals go on top of that—and this PCB is already selling abroad, though specifically packaged and detailed by companies like Comar and SevenStar. You won't see SRT-branded Class Bs, but it may be valuable to understand its position behind the scenes as we begin to experience the technology.

You see, there may be performance issues, or at least "growing pains" in Arroyo's words, with these purposely low-powered (2-watt) and slow-talking transponders. Creating the Class B standard was delayed as the authorities struggled to ensure that the Class A system, working so well, would never be disrupted by a congestion of smaller, B-talking recreational boats. In fact, the B standard, finalized in early 2006, uses a communications protocol and message slots slightly different from Class A. Simulations indicate overall system integrity, but the true test won't happen until a lot of real Class B transponders are in use. In the meantime, several short-term glitches are apparent and worth knowing about.

For one thing, existing AIS target plotters may not recognize all Class B data, particularly the static variety—boat name, type, dimensions, etc.—which is now slotted differently than anticipated in the original standard. In other words, your plotter, not to mention those on ship bridges, may show a Class B target moving across the screen—the dynamic data—but not its name, etc., until the plotter's software is updated to understand the final B specs.

Now is a good time to mention that not all ships plot even Class A AIS targets as well as you might think, a fact that concerns navigation experts like Andy Norris, who chairs one of the international committees concerned with such matters. Class A transponders constantly must monitor both AIS frequencies, but their mandated minimum display is just three lines of text describing the nearest targets, and that's all some economy-grade bridges have (and some personnel don't even monitor that). Frankly, yours truly was naive on this point, which underlines Norris' worry that recreational boaters will presume greater Class B transponder visibility than may actually exist. On the other hand, bear in mind that many ships have superb AIS target displays, even able to "fuse" them with radar targets, and these will be mandated on all large vessels over the next few years.

This article originally appeared in the March 2007 issue of Power & Motoryacht magazine.

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