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Author Topic:   USCG Requests Feedback on AIS Aids to Navigation
jimh posted 03-14-2014 11:16 AM ET (US)   Profile for jimh   Send Email to jimh  
The United States (of America) Coast Guard announced last month (on February 2, 2104) that it would in the near future begin test transmission of AIS messages for a new category of aid to navigation (AtoN) called AIS AtoN, a sort of virtual and electronic-only navigation marker. The USCG issued the following statement on their NavCenter website:


U.S. Coast Guard to Test Automatic Identification System (AIS) Aids to Navigation (AtoN)

In the near future, the U.S. Coast Guard and other authorized agencies and organizations (i.e., U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, Marine Exchange of Alaska) will begin transmitting AIS AtoN messages and marine safety information via AIS for testing and evaluation. The exact content, location, and times of these broadcasts will be announced in future Local Notices to Mariners.

AIS is an internationally adopted radio communication protocol that enables the autonomous and continuous exchange of navigation safety related messages amongst vessels, lifeboats, aircraft, shore stations, and aids to navigation (AIS AtoN). AIS AtoN stations broadcast their presence, identity (9-digit Marine Mobile Service Identity (MMSI) number), position, and status at least every three minutes or as needed. These broadcasts can originate from an AIS station located on an existing physical aid to navigation (Real AIS AtoN) or from another location (i.e., AIS Base Station). An AIS Base Station signal broadcasted to coincide with an existing physical aid to navigation is known as a Synthetic AIS AtoN. An electronically charted, but non-existent as a physical aid to navigation, is identified as a Virtual AIS AtoN. The latter two can be used to depict an existing aid to navigation that is off station or not watching properly or to convey an aid to navigation that has yet to be charted. All three variants can be received by any existing AIS mobile device, but they would require an external system for their portrayal (i.e., AIS message 21 capable ECDIS, ECS, radar, PC). How they are portrayed currently varies by manufacturer, but the future intention is for the portrayal to be in accordance with forthcoming International Standards (i.e., IEC 62288 (Ed. 2), IHO S-4 (Ed. 4.4.0)).

Mariners capable of receiving and displaying these test AIS messages are encouraged to provide feedback and report any anomalies to the USCG NAVCEN Website: | Contact Us Tab | Subject: AIS | Category: AIS Testing.


jimh posted 03-14-2014 11:44 AM ET (US)     Profile for jimh  Send Email to jimh     
The AIS AtoN devices will be of three characteristics: real, synthetic, and virtual.

A real AIS AtoN is an actual physical aid to navigation, such as a buoy, a day mark, or a light house, whose actual position is transmitted as an AIS message. The AIS transmission originates from the actual physical location of the aid.

A synthetic AIS AtoN is also an actual physical aid to navigation, but the AIS transmission originates from a base station nearby, not from the physical location of the aid itself.

A virtual AIS AtoN has no physical manifestation. There is no buoy, day mark or tower, but only an AIS signal. The AIS signal originates from a nearby AIS base station.

In order for these AIS AtoN signals to be received, the AIS receiver and the associated display device must be capable of decoding AIS messages of Type 21. Not all recreational chart plotters are necessarily assumed to be capable of properly handling AIS messages of Type 21.

Further, assuming that a recreational chart plotter can handle and decode AIS messages of Type-21, the manner in which they will present an AIS AtoN described in those messages on a chart display is also likely to be variable.

In order for recreational boaters to participate in the USCG request for feedback, it will be necessary to have an AIS receiver and chart plotter that can handle AIS Type 21 messages. It will also be necessary to be in range of the AIS transponders that will be sending these signals.

padrefigure posted 03-14-2014 12:17 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
Any idea which recreational chart plotters are capable of receiving, translating, and displaying Type 21 messages?
jimh posted 03-14-2014 01:06 PM ET (US)     Profile for jimh  Send Email to jimh     
I am fairly confident that most AIS receivers will be pleased to receive an AIS Type-21 message and output the received data. The problem will be in the chart plotter receiving the AIS message. I suspect that many recreational chart plotters may not know what to make of a Type-21 message.

At the moment, I don't have any source of a Type-21 message to test with. I have written to the support website for my chart plotter to see what they have to say about display of Type-21 messages. As soon as I have an answer from them, I will post the information. Perhaps several readers could do the same for their particular brand and model of chart plotter, and we could collect the data here.

I have written to:

Polar Navy regarding PolarViewNS

and to

Lowrance regarding HDS Gen1 chart plotters.

jimh posted 03-15-2014 08:24 AM ET (US)     Profile for jimh  Send Email to jimh     
For the type of AIS AtoN the USCG refers to as a real AIS AtoN, there will be an AIS transponder on the actual aid to navigation. The transponder will need electrical power to operate, and, if the aid to navigation is a floating aid, such as a buoy, this electrical power will have to be carefully managed.

Typically an AIS AtoN transmitter will have a power output of about 2-Watts. Unlike lighted buoys, whose lamps are only illuminated during darkness, an AIS AtoN will have to operate its transmitter continually, day and night.

A further problem for a floating AIS AtoN is the power consumed by its AIS receiver. It may be necessary for a floating AIS AtoN to also have an AIS receiver in continual operation. The transmission of AIS signals is done by coordination of all AIS transponders in range of each other. For the AIS AtoN to know when it should transmit, it would have to listen for AIS traffic in its local area, and then coordinate its transmission.

An alternative method is for a floating AIS AtoN to be designed to work in tandem with a base station. The base station will transmit an AIS signal that includes data informing other AIS transponders to reserve a time slot in their time-shared network for the AIS AtoN. The AIS AtoN can then always transmit in the reserved time slot. It would not have to continually listen for local AIS traffic and fit itself into the slot pattern. This approach can conserve power drain by reducing the receiver operating time.

Also, the AIS AtoN must operate a GPS receiver so that it can know the actual position to send in its AIS broadcasts.

Chuck Tribolet posted 03-15-2014 02:17 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
However, the AIS AtoN doens't need that 2W 7/24. It only
needs the 2W in its time slot. The duty cycle is pretty low.


jimh posted 03-15-2014 02:38 PM ET (US)     Profile for jimh  Send Email to jimh     
A recreational boat grade Class-B transponder says its average power consumption is 170mA at 12-VDC, or about 2.1-Watts.

Compare at: pdf Page 29

jimh posted 03-16-2014 09:44 AM ET (US)     Profile for jimh  Send Email to jimh     
The power consumption of an AIS AtoN will be related to

--the need to have a receiver listening for traffic on the AIS channels all the time

--the frequency at which its transmitter is actually operating

The least power consumption will be for an AIS AtoN that is working in tandem with a base station that is reserving the transmit time slots, and thus does not have an AIS receiver running, and the AIS AtoN only transmits its position in those reserved time slots once every three minutes. (In AIS, the frequency at which an AIS transponder sends its position is a function of how fast it is moving. Rapidly moving vessels transmit their position more often than slow moving vessels. Apparently AIS AtoN, which are not moving at all, only transmit every three minutes.)

The SRT company has such a device, their CARBON model for AIS AtoN applications, and they rate the power consumption as less than 0.1-Ampere-hour per day in certain modes.

Compare at AtoN%206pp%20brochure%20PRESS%2011.10.13.pdf

A very good overview of AIS Aid to Navigation can be found at

The above publications sets out the three general types of AIS AtoN:




For the real category, it sets out three types:

--Type 1: transmit only station

--Type 2: similar to Type 1 but with a receiver for remote configuration

--Type 3: full transmit and receive station

All three types of real AIS AtoN are able to "switch off and sleep" between transmission to conserve power.

In addition to just sending their identification and position, a real AIS AtoN can also send sensor data. The sensor can provide data on weather, tides, and sea state.

A significant benefit of a real floating AIS AtoN is the confirmation of the position of the aid. For example, a floating buoy with an AIS AtoN can confirm its position as being on station.

jimh posted 03-16-2014 09:54 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the three-minute transmit interval: I have not found that mentioned in any official specifications, but it is mentioned in some literature about the SRT Carbon Type-1 AIS AtoN device at

under the "Specification" tab:

'Power consumption: from 0.1Ah/day (Type 1 AtoN with 3 minute position reporting rate)"

In that same place under the "Overview" tab the device power consumption is also mentioned:

"It exhibits by far the lowest power consumption requirements in the market place at 0.06 Ah/day (Type 1) and 0.5Ah/day (Type 3)."

That is really rather remarkably low power consumption. I guess if a floating aid has enough battery power to run a lamp all night, it will be able to run a Type-1 AIS AtoN without too much trouble.

jimh posted 03-16-2014 11:27 AM ET (US)     Profile for jimh  Send Email to jimh     
The technical term for the frequency of transmission of an AIS transponder is reporting interval. The reporting interval is given in a standard, ITU-M.1371-4, "Technical characteristics for an automatic identification system using time-division multiple access in the VHF maritime mobile band." There are two general categories: Class A shipborne transponders, and all other transponders. Here is a summary of the reporting intervals:

Class A shipborne
Ship at anchor or moored and not moving faster than 3-knots = 3-minutes
Ship at anchor or moored and moving faster than 3-knots = 10-seconds
Ship 0 to 14-knots = 10-seconds
Ship 0 to 14-knots and changing course = 3.3-seconds
Ship 14 to 23-knots = 6-seconds
Ship 14 to 23-knots and changing course = 2-seconds
Ship faster than 23-knots = 2-seconds
Ship faster than 23-knots and changing course = 2-seconds

Other than Class A shipborne
Class B "SO" not moving faster than 2-knots = 3-minutes
Class B "SO" moving 2 to 14-knots = 30-seconds
Class B "SO" moving 14 to 23-knots = 15-seconds
Class B "SO" moving faster than 23-knots = 5-seconds
Class B "CS" not moving faster than 2-knots = 3-minutes
Class B "CS" moving faster than 2-knots = 30-seconds
Search and rescue aircraft = 10-seconds
Aids to navigation = 3-minutes
AIS base stations = 10-seconds

"SO" means self-organizing time division multiple access or SO-TDMA; "CS" means carrier sense time division multiple access or CS-TDMA.

Source: itu-m.1371-4-201004.pdf
See Table 1 and Table 2 on page 4.

jimh posted 03-17-2014 03:13 PM ET (US)     Profile for jimh  Send Email to jimh     
I asked Lowrance support:

Will my HDS-8 Gen1 display AIS targets described in AIS Type 21 messages?

Lowrance support replied:

Yes, our Gen1 units use the AIS Type 21 message.

By inference, I suggest that this means all the HDS Gen1 and Gen2 chart plotters will show AIS targets described in Type 21 messages, and it is also likely that the similar SIMRAD chart plotters will, too.

Now I just need a source of some AIS AtoN Type-21 messages to test my HDS. I will watch the USCG website for more information on announcement of some tests and the location.

jimh posted 03-18-2014 09:00 AM ET (US)     Profile for jimh  Send Email to jimh     
I asked Polar Navy (developer of PolarView NS):

Does the present version of PolarView NS know how to handle AIS messages of Type-21? Will it display aids to navigation whose position is sent by Type-21 AIS messages?

Polar Navy replied:

At this time PolarView does not display non-vessel AIS targets.
jimh posted 03-20-2014 01:21 PM ET (US)     Profile for jimh  Send Email to jimh     
I had some correspondence with the USCG about the present marketplace of recreational chart plotters and their ability to show AIS AtoN targets. The USCG expressed confidence that, now that they have begun to broadcast AIS AtoN messages, the marketplace will diligently upgrade or bring to market equipment that can decode AIS AtoN messages.
jimh posted 07-19-2014 02:42 PM ET (US)     Profile for jimh  Send Email to jimh     
I was hoping that the Coast Guard might deploy an AIS aid to navigation in the Great Lakes region, and, if they did, I would have tried to receive it in order to see if its position showed up on my two chart plotters. So far, as best I can tell, there are no Aids TO Navigation (ATONs) using AIS anywhere close to me, but there are plenty in the San Francisco area. Accordingly, I would like to encourage anyone in the vicinity of the Golden Gate Bridge with an AIS receiver and a chart plotter (that are connected together) to test their system. Check to see if the AIS ATON's show up on the chart display of your recreational grade plotter.

You can see where these AIS ATONs are located by using MARINETRAFFIC.COM. On their website you will find the AIS ATONs marked with distinctive (pink) icons. There are about 17 AIS ATONs in the region. I would appreciate hearing any reports of how they display (or do not display) on various recreational-grade chart plotters.

jimh posted 07-19-2014 02:52 PM ET (US)     Profile for jimh  Send Email to jimh     
In addition to the San Francisco area, the USCG appears to have also deployed a few AIS ATONs in the following areas:

--several on the Mississippi River from New Orleans to Baton Rouge;

--one offshore from Astoria, Oregon;

--two around Seattle, Washington.

To anyone in those areas with an AIS receiver connected to a recreational chart plotter, I invite you to also check to see if these AIS ATONs are showing up on your chart plotter due to reception from an AIS receiver.

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