Plug Prayers Answered Page 3

Electronics — August 2005
By Ben Ellison

Plug Prayers Answered
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Should I get a full AIS transponder or just a listener? X.G, via e-mail
I’ve heard knowledgeable navigators opine that for small- to medium-size yachts, an Automatic Identity System (AIS) receiver provides 90 percent of the safety value you might get by also broadcasting your own location and motion. But those gentlemen are cynics who believe that ships just don’t alter course for yachts, so why bother showing them where you are? I have more respect than that for (most) commercial mariners. If I were going to spend much time in waters frequented by the big vessels currently mandated to carry AIS, and if I could afford it, I’d have a full transponder.

However, that second “if” is a biggie. Currently available Class A AIS units cost upward of $4,000 and can entail serious additional installation expense. Besides antennas and power, they need NMEA 0183 input from GPS, electronic compass, and speed transducer, any one of which may lack the horsepower to send data to yet another device. Then there’s the special, fast 0183 output to the various radars, plotters, and PCs where you might want to see the targets (you end up “seeing” what the transponder “hears”). Picture a lot of connections, a lot of possible points of failure, and another way NMEA 2000 can improve marine electronics. In addition, the powers that be are still working on a Class B AIS standard, and while it should bring down unit costs, there’ll be a lag between the finished standard—expected later this summer—and actual equipment.

By contrast, AIS listeners aren’t subject to standards or FCC approvals or complicated installations, and I sense that we’re about to see the field of available products explode. Si-Tex just announced an AIS Radar product that has its own little screen and retails at $700, as well as a $500 black-box “engine” that will plot AIS targets on several Si-Tex plotters or on a PC running a growing number of AIS-capable charting programs. I hear we’ll soon see a combination AIS listener and GPS that uses USB for power and data. And Nobeltec, perhaps the first company to offer AIS listening to yachts, just cut a third off the price of its receiver. So while 90 percent is an exaggeration, it’s surely easier to just listen to AIS.

Got a marine electronics question? Write to Electronics Q&A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: For fastest response, visit the Electronics forum at No phone calls, please.

Next page > Raymarine H6 > Page 1, 2, 3, 4, 5, 6, 7

This article originally appeared in the August 2005 issue of Power & Motoryacht magazine.

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