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ContinuousWave: Small Boat Electrical
FCC Announces Approval of Class-B AIS
|Author||Topic: FCC Announces Approval of Class-B AIS|
posted 09-22-2008 05:49 PM ET (US)
The Federal Communications Commission (FCC), a government regulatory agency that oversees and regulates all radio transmitters in the United States of American, has announced it has decided to approve Automatic Identification System (AIS) Class B transponders. See
posted 09-22-2008 06:09 PM ET (US)
Got the Readers Digest version?
That's from someone who can read these publications. Yikes!
posted 09-22-2008 08:58 PM ET (US)
The legal jargon isn't really important. Class B AIS has been in operation globally, except in the United States of America Now we are going to be able to have AIS transponders on small boats. The cost is currently about $1,000, but I imagine that this might fall with higher production levels.
posted 09-22-2008 10:31 PM ET (US)
I read most of the PDF from Jim's link. I was particularly curious about what security standards would need to be met to insure the safety of the network from threats.
I do agree with the discussion that the Marine Mobile Service Identity (MMSI) should probably not be handed out by BoatUS for the end user to program and should be filed with the Federal Communications Commission when you purchase a radio for a particular vessel. (Section 31)
I don't have enough faith in the marine electronic retailers to trust them handling this sensitive information.
posted 09-23-2008 09:16 AM ET (US)
There are probably more recreational boats in the United States of America than anywhere else, so it is likely that there will soon be more Class-B Automatic Identification System transponders in the United States of America than anywhere else. On that basis it will be interesting to see if the Federal Communications Commission's requirement that they cannot be user-programmed with their Marine Mobile Service Identity and static data turns out to be a nuisance or a blessing.
posted 09-24-2008 12:33 AM ET (US)
The complexity of an Automatic Identification System transponder is about the same as a
Digital Selective Calling (DSC) Very High Frequency (VHF) radio, so IF the volumes are there, the prices should
be about the same. Volume vs. price is a chicken/egg problem.
A question for the Radio Frequency (RF) mavens: Could Automatic Identification System be built into a
I don't see a problem with Boat US handing out the Marine Mobile Service Identity,
Will I get an Automatic Identification System transponder? No. Where I boat, there's
|Tom W Clark||
posted 09-24-2008 12:49 AM ET (US)
Over the last seven years, there are very few instances here on ContinuousWave when this is literally true:
I have no idea what you guys are talking about.
posted 09-24-2008 09:20 AM ET (US)
To use the same antenna for receiving and transmitting simultaneously a Duplexer is needed. And there has to be some frequency separation between the transmit and receive frequencies. At 156-MHz the resonant circuit components are generally too large to be feasible for inclusion inside a radio cabinet. Most implementations use large cavity resonators which are often 1/4-wavelength--about 18-inches. Also the Automatic Identification System frequency is relatively close to the rest of the channels in the Very High Frequency Marine Band.
Channel 1 of the Very High Frequency Marine Band is 156.050-MHz. The Automatic Identification System Channels are 161.975 and 162.025. The channel separation there is about 5 to 6-MHz. That would certainly be feasible to adapt to an antenna duplexer. However, the receive frequency of some of the higher split channels are in the range of 161.8 to 161.9 MHz. That's very close.
A good chart is found at http://www.navcen.uscg.gov/marcomms/VHF.htm
posted 09-24-2008 09:29 AM ET (US)
Tom--We're talking about the Automatic Identification System. It is a system in which an active radio transponder transmits vessel identification, course, speed, and all sorts of other data. There are two categories:
Class-A transponders are required on all large commercial vessels in U.S. waters (and around the globe).
Class-B transponders are optional on smaller vessels, including recreational vessels.
Anyone can receive and monitor Automatic Identification System transmissions with a Receive-only Automatic Identification System. This allows a vessel to discover and identify other vessels within about a ten mile radius. Most modern chart plotter devices can display Automatic Identification System information on their plot displays, or a dedicated Automatic Identification System plot display, something like a RADAR screen, can be used.
For more information see
The big event here is the announcement that the Federal Communications Commission is going forward toward authorization of Class-B Automatic Identification System equipment in the United States of America For several years now only Class-A equipment was authorized. This effectively prevented most recreational boaters from participating in Automatic Identification System due to the high cost of a Class-A Automatic Identification System transponder installation, which was typically $5,000 or more.
An Automatic Identification System receive-only device is currently only about $250. See
for links to some Automatic Identification System receive-only device manufacturers.
|Tom W Clark||
posted 09-24-2008 09:49 AM ET (US)
Jim - Thank you for the explanation.
posted 09-24-2008 03:54 PM ET (US)
This is really cool. When I buy my next chartplotter for the boat, I'll be sure it has Satellite Weather overlay capability as well as this Automatic Identification System technology. This could solve your "really big headaches" in fog: Freighter traffic. You'd still have to excercise caution, as it isn't as good as Radio Detection and Ranging (RADAR) gear. (You thought you had me, didn't you?!).
posted 09-24-2008 10:35 PM ET (US)
To add to my comment above, I meant to say that AIS, while an improvement to and important element of modern navigation in weather and crowded comercial waterways, still won't take the place of RADAR, which identifies EVERY object near you, not just the ones transmitting AIS signals.
I'd actually like to see it eventually become mandatory that a boater equip the vessel with electronics that transmit AIS signals, so that the system is most effective.
posted 09-25-2008 12:08 AM ET (US)
Dave--There has been some argument about the spreading of AIS to non-mandatory carriage vessels. The issue divides along these lines:
--it would be best if every vessel had AIS so we could all be aware of each other, or
--if all vessels have AIS transponders the display in busy areas will be too cluttered to be useful.
There are also technical concerns raised about the capacity of the system to allow for a high number of vessels in one area, and also for the usefulness of the data from Class-B transponders, which do not transmit as often or send as much data.
AIS uses a very interesting protocol for its communications scheme, using a technology called Self-Organized Time Division Multiple Access (SOTDMA or STDMA). This allows groups of vessels which happen to encounter each other on the high seas or elsewhere to integrate their transponders into a sort of ad-hoc network in such a way that they do not interfere with each other.
ASIDE: Curiously, there is a dispute about this intellectual property. See
for some of the details.
FInally, there seems to be a sort of hysterical concern that AIS amounts to a big-brother invasion of privacy for recreational vessels and you'd be nuts to get one to facilitate the government keep closer watch on your while you are boating.
posted 09-25-2008 09:43 AM ET (US)
A good description of the AIS is given in
and reading it will provide a thorough background on the AIS. Also the Coast Guard has a good website with excellent information at
posted 09-25-2008 08:43 PM ET (US)
[Removed sidebar discussion on acronym use.]
posted 09-27-2008 08:31 AM ET (US)
I was out on Lake St. Clair over Labor Day Weekend and parts of the lake were almost paved over with boats. I can't imagine how the system can handle that amount of traffic nor how the display would remain intelligible.
posted 09-28-2008 09:41 AM ET (US)
In crowded conditions with recreational boats a visual watch could be more effective, IMO. However, if desired, displays could be simplified by using a shorter range or by zooming in to thin out the number of signals displayed.
Software for displays could also allow for some discrimination based upon user needs. Perhaps it could be set to display vessels of a certain size or on a course such that a collision could occur unless action is taken.
IMO, a system need not display every vessel in your waters in order for it to improve boating safety.
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