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Author Topic:   AIS Search And Rescue Transmitters

jimh posted 11-29-2014 08:30 AM ET (US)
[I separated this discussion from another topic, Marine Mobile Service Identities.]
In c.2010 a new type of emergency locating radio device was created by international agreement. These devices are called Automatic Identification System Search and Rescue Transmitters or AIS SART for short. An AIS SART has its own modern and advanced GNSS receiver which has a very fast time to first fix (TTFF), allowing the device to quickly deduce its own position once activated. The SART AIS then transmits an AIS message, broadcasting its position and identity on the regular AIS channels. Any vessel or shore station in range of the VHF Marine Band radio transmission that is monitoring with an AIS receiver or has an AIS transponder will be notified of the distress. Note that these devices do NOT send a digital selective calling (DSC) distress alert message. The AIS message they send is only going to be received by stations or ships with AIS receivers or transponders.
Hoosier posted 11-28-2014 09:36 AM ET (US)
Here's an AIS SART device I stumbled on. This is really cool:
http://www.westmarine.com/buy/ mcmurdo--smartfind-s10-personal-ais-beacon--13342605
It is part of the GMDSS and offers all the benefits of it with the added advantage of the units being low cost and very portable.
jimh posted 11-28-2014 12:01 PM ET (US)
The Personal AIS Emergency device utilizes an MMSI for identification. Let me explain this briefly--I am working on a more comprehensive explanation of MMSI numbers that I hope to publish soon based on ITU RRecommendations.
In the MMSI number space created with its nine-character 0-9 digits, there is a further subdivision as follows:
For "Devices using a freeform number identity", and in the sub-group, "Man overboard" devices, such devices will use an MMSI that consist of the following sequence:
972XXNNNN
Here the prefix "972" indicates the nature of the device: man-overboard device.
The XXis a two-digit manufacturer identification code 01 to 99;
The NNNN is four-digits 0 to 9 with a sequence number. When a manufacturer runs out of sequence numbers, they apply for another manufacturer identification code and restart their sequence number.
For "Devices using a freeform number identity", and in the sub-group, "Emergency position indicating radio beacon-automatic identification system" devices, such devices will use an MMSI that consist of the following sequence:
974XXNNNN
Here the prefix "974" indicates the nature of the device: EPIRB-AIS device,
The XX is a two-digit manufacturer identification code 01 to 99;
The NNNN is four-digits 0 to 9 with a sequence number. When a manufacturer runs out of sequence numbers, they apply for another manufacturer identification code and restart their sequence number.
In these assignments, the MMSI indicates the identity of the device itself, not the identity of the ship it might be associated to. Like the 406-MHz EPIRB, these AIS-EPIRB devices have identities pre-established at the manufacturer, and the user does not enter their own MMSI. The user apparently must register their ownership in some manner. Let me see if I can find how that works.
Note that in this numbering space there are only 000 to 9999 available for discrete identifications for each manufacturer code. There are only 00 to 99 available for manufacturer codes. This number space runs out of identities when 100 x 10,000 = 1,000,000 devices are manufactured. This does not seem like a very large number space for these devices, particularly compared to the vastly larger number space of the hexadecimal 15-digit 406-MHz EPIRB devices.
jimh posted 11-28-2014 12:18 PM ET (US)
I found NO information about registering an AIS-EPIRB device. Apparently when you activate the device it quickly gets a position fix from its own GNSS receiver, then begins transmitting on the AIS channel with its own MMSI. I assume there is something in the AIS specification that provides for a special category for this device so it draws some attention on an AIS display. I will have to research that, too. There is a lot of room in the AIS message structure to send data. The real concern is what sort of response will occur on an every-day recreational-grade chart plotter connected to an AIS receiver. That might be interesting to investigate.
jimh posted 11-28-2014 01:40 PM ET (US)
The AIS-SART device that David links (above) is apparently on the cutting edge. I found a Radio Technical Commission for Maritime Services (RTCM) presentation from a 2014 "manufacturers workshop" that says one of the goals of the organization is to work "towards an EPIRB AIS standard."
I am guessing that an AIS-EPIRB is going to send an AIS MESSAGE #1 (CLASS A POSITION REPORT) and set the value of NAVIGATION STATUS to be "AIS-SART is active." This is about the only place in an AIS message that there is a place for an AIS search beacon transmitter, as far as I can see. If anyone has a better suggestion, please mention it.
For reference, see
http://www.navcen.uscg.gov/?pageName=AISMessagesA
and see the options for data content in the field NAVIGATION STATUS. A data value of "14" is reserved for "AIS-SART (active), MOB-AIS, EPIRB-AIS."
For these devices to have value, the ships that are receiving their signal must have some sort of display device (and perhaps even an alerting method) to indicate that the AIS target is a rescue AIS transmitter; without the coordination of the display processing the AIS data, no one will pay special attention to this AIS signal, it would seem.
Don SSDD posted 11-28-2014 09:42 PM ET (US)
My friend who owns the 25 Guardian has a [what turned out to not be an AIS SART but rather a 406-MHz personal locator beacon].
jimh posted 11-28-2014 11:52 PM ET (US)
An AIS SART manufacturer, WEATHERDOCK of Germany explains how their device works:

quote:
Function
Being activated, the easyONE [the model name of this AIS SART device] starts transmitting a full AIS MOB emergency message. This contains the individual unit ID, current GPS position, als well as COG and SOG of the victim. Because the unit ID starts with "972...", each AIS receiver within range of 7 to 8 nautical miles (bad conditions and height of receiving antenna may lower range) identifies this emergency message. The connected chart plotter or PC screen will display the official MOB symbol (red X with red circle).
Two LEDs show functionality of the unit easily. This will ease the usage in situation of distress.
If the easyONE is triggered once, the battery capacity will last for more than 36 hours of continously transmitting. Because of this and [its] palm size the AIS MOB easyONE is the perfect companion.
The easyONE is ready to use and there is no registration or license needed.
Source: http://www.easyais.com/en/products/ais-s-a-r-t/a109-easyone/
Several important disclosures there:
--the AIS transmission from any AIS transmitter with an MMSI of 972-prefix is apparently supposed to be immediately considered to be an emergency alert for man overboard or other distress. If a device with MMSI 972-prefix is only activated if there is a distress situation. I am very curious to see if my run-of-the-mill recreational chart plotter can properly respond to reception of an AIS message coming from a transmitter with MMSI beginning 972xxnnnn and perform the appropriate identification of this source as an emergency message.
--there is no registration or license needed. Apparently these AIS SART transmitters are just considered an emergency or distress alert, and likely to be from someone in the water (or soon to be in the water).
--as mentioned in the tab "techincal details" the message sent is AIS MESSAGE #14 SAFETY MESSAGE and the message text is either "MOB ACTIVE" (in real use) or "MOB TEST" (in test mode). For details of AIS MESSAGE #14 see
http://www.navcen.uscg.gov/?pageName=AISMessage14
I will also be curious if my run-of-the-mill recreational chart plotter will display the AIS MESSAGE #14 message text contents. (I seriously doubt it will, as it can't even display routine message text correctly.)
jimh posted 11-29-2014 12:27 AM ET (US)
Here is a recording showing the response of a GARMIN GPSmap 720S chart plotter connected via NMEA-2000 to a Garmin AIS300 receiver when an WEATHERDOCK AIS SART broadcast is received:
https://www.youtube.com/watch?v=HuosuRavqRU#t=24
Spool ahead to the 1:00 mark to see the actual demonstration if you don't want to sit through the explanatory remarks that precede it. (It is in French, so perhaps not completely intelligible to many English-only viewers.)
The chart plotter responds with an on-screen alert box and an aural alarm sounding. Nice work on handling the transmission from this relatively very new AIS device--that's is what you expect from Garmin.
Another recording shows a similar demonstration. This time the AIS receiver is part of a VHF Marine Band radio made by NAVICOM, a model RT650, and the data link between receiver and chart plotter is via NMEA-0183. The results are similar. Spool in to 0:40 to see the demonstration:
https://www.youtube.com/watch?v=zKk75w2VTsg
(Again, narrated in French.)
And the perfect demo: no narration, and right to the point:
https://www.youtube.com/watch?v=uPaznf_Qzy8
And it is almost three years old! These Europeans seem way ahead of us here in North American and USA on this technology.
jimh posted 11-29-2014 12:57 AM ET (US)
A few more technical details of the general AIS SART devices:
--the transmitter power is 1.5 to 2-Watts
--the AIS message is sent eight times per minute; this helps insure a message might be sent when the man overboard is at a wave crest, increasing the height of the transmitter in the waves and improving its range
--the battery power lasts from 24-hours to as much as 96-hours
jimh posted 11-29-2014 08:56 AM ET (US)
There seems to be two general types of AIS SART devices:
--manually activated devices which require someone to push or hold a button to activate the device, and
--automatically activated devices, which start operating as soon as they detect that they have been immersed in water.
jimh posted 11-29-2014 09:24 AM ET (US)
One limitation of an AIS SART is the need for a would-be responder to be monitoring for AIS transmissions. Let's briefly look at several methods of sending an emergency distress alert and how many people might receive it:
The oldest method of making a radio emergency transmission: you make a MAYDAY call on voice on Channel-16. In theory, every boat or ship with a VHF Marine Band radio is supposed to be maintaining a radio watch on Channel 16 at all times, so any vessel in radio range with a VHF Marine Band radio should hear your transmission. Not all vessels actually maintain a constant radio watch on Channel 16, so your distress call might be missed.
A newer method of emergency alert: you make a DSC distress alert transmission. This transmission should be received by every boat or ship with a DSC radio in range. For the last ten years most VHF Marine Band radios on the market have had DSC capabilities of some sort, so just about every boat with a radio not more than ten years old should be capable of receiving a DSC distress alert. Since DSC radios are keeping a continual watch for DSC calls, your distress alert has a good chance of being received on any DSC radio that is turned on and is in range. The DSC radio also stores the data it receives, so the operator of the radio can retrieve it and review it.
This newest method being discussed here: you activate an AIS SART transmitter. Only vessels with an AIS receiver or AIS transponder in radio range will receive your message. Also the Coast Guard of the USA has an extensive system of AIS base stations, and if you are in their coverage area (which is mainly coastal waters and the Great Lakes) the Coast Guard should receive your AIS SART transmission. [The concern is what the Coast Guard will do in response; this is discussed further, below.] The number of recreational vessels with AIS receivers or transponders is only a small fraction of total radio-equipped recreational vessels.
Hoosier posted 11-29-2014 10:36 AM ET (US)
I was surprised to see it when I went looking for PLBs. I think they are a neat device especially since an AIS receiver is becoming a common standard feature in new radios and chartplotters. Even the relatively low end Link 8 and Elite series from Lowrance has AIS as a standard feature. What’s missing from the low end is a cheap general purpose AIS transmitter, this may be the beginning for that.
jimh posted 11-29-2014 12:28 PM ET (US)
Yes, to paraphrase a classic limerick:
A friend, both older and kinder,
Gave us this important reminder:
In an A-I-S SART
You have all the best parts
Of a shipboard Class-B Transponder!
Hoosier posted 11-29-2014 01:43 PM ET (US)
This really is a whole new area for recreational boats. How does Rescue 21 deal with AIS? Oh, remember this discussion?
http://continuouswave.com/ubb/Forum6/HTML/003493.html
It's starting to look like there's a trend towards "the Giant Vacuum Cleaner in the Sky" approach to everything, all under the guise of keeping us "safe". At some point the old Mk 1 Eyeball has to take over from technology and let common sense rules keep us out of trouble.
jimh posted 11-29-2014 04:09 PM ET (US)
Let's keep this discussion on AIS SART. If you want to add something to the other conversation, you can revive it. It might be better to revive this thread:
http://continuouswave.com/ubb/Forum6/HTML/003660.html
It is a more recent discussion and analysis of non-radio-transmission AIS computer applications being developed by the Department of Homeland Security.
Hoosier posted 11-29-2014 07:41 PM ET (US)
When we were in the North Channel this summer I found it interesting, and annoying, that so many Canadian vessels had AIS transpnders on them. The AIS alarm on my Link-8 was going off all the time until I finally turned it off. I'm now thinking it could become a case of the data become just so much noise that no one will pay attention to it and they will turn off their CPA alarms or set them so tight that they'll be usless.
jimh posted 11-30-2014 09:05 AM ET (US)
I have made inquiries with navigation software makers, navigation hardware makers, and the USCG to ask about support for the AIS messages from an AIS SART device. I suspect that there will not be at present completely universal support for these types of AIS target. I was quite impressed that some older-generation chart plotters seen in the recorded presentations appeared to competently report the AIS SART target.
jimh posted 11-30-2014 04:08 PM ET (US)
AIS SART devices transmit on the VHF Marine Band, on the AIS channel, and they can be received by any vessel nearby with an AIS receiver. AIS receivers are now routine options on VHF Marine Band radios, increasing the probability that a nearby vessel will be able to receive the transmissions.
Since the nature of these devices is to be used in man-overboard (MOB) situations, any vessel having an AIS SART would, correspondingly, be very likely to have an AIS receiver that could receive the transmission from an AIS SART that was deployed and activated. It would make no sense for a vessel to carry an AIS SART and not have an AIS receiver or AIS transponder that could receive the signal from the AIS SART.
In stark contrast, is you are the man-overboard and you have a 406-MHz locator beacon, there is a very low probability that the vessel you just fell from into the sea has any radio direction finding equipment or can even receive the 406-MHz transmission. Your 406-MHz beacon signal will have to be relayed to rescue agencies via a complicated communication system of satellite to satellite, satellite to earth station, earth station to data network, and data network to terminal. At that point, some administrative process has to be initiated to attempt to contact the owner of the beacon device, who should have registed himself, and his identity must be retrieved some sort of database maintained on a global basis. While all this is going on, the boat you just fell off has no access to any of this data.
With AIS SART, there is a very good probability that the boat you just fell off has an AIS receiver that will show the people on board where you located within about 50-feet, as long as you're within five miles of the boat. And, if the AIS SART is an automatic activation type, the AIS SART should be activated automatically as soon as the MOB hits the water. (It may take a minute for its GNSS receiver to get a position fix.)
jimh posted 11-30-2014 04:45 PM ET (US)
This topic of AIS SART devices gets more interesting the deeper into it I delve. The transmitting pattern of the AIS SART is often described to be a transmission of eight messages in one minute. There seems to be more complexity to it that just that. The eight messages are divided into four on the AIS A-channel and four on the AIS B-channel. And all eight messages are sent within a 14-second interval. Apparently, this 14-second periodicity was intended to coincide with typical wave periods, so that there is a higher probability that one of the messages is sent from the crest of a wave.
The personal or MOB AIS SART is assigned its own MMSI so there is no confusion between an AIS transmission from a ship and from the MOB device.
jimh posted 11-30-2014 05:12 PM ET (US)
Regarding how an agency like the Coast Guard will treat an AIS SART transmission, I found this document:
http://www.navcen.uscg.gov/pdf/AIS/0510.pdf
The salient point seems to be:

quote:
Usage During Emergencies - With respect to using AIS safety related text messages in emergency situations, users must be aware that they may not be received, recognized or acted upon as Global Maritime Distress Safety Systems (GMDSS) messages would be by the Coast Guard, other competent authorities or maritime first responders. Thus AIS must not be relied upon as the primary means for broadcasting distress or urgent communications, nor used in lieu of GMDSS such as Digital Selective Calling radios which are designed to process distress messaging.
That document is a few years old. I don't know if there has been an update.
jimh posted 12-07-2014 07:30 AM ET (US)
I asked the USA Coast Guard about the expectations for RESCUE21 radio watch standers to monitor for AIS SART transmissions. They responded that Search and Rescue Transmitters (SARTs) are not distress alerting devices, but, rather they are homing devices. Homing devices are used by on the scene responders to help locate a vessel in distress, a man overboard, or a life raft.
RESCUE21 watch standers will be a notified of distress situations by distress alert devices like a DSC distress alert transmission.
There is distinction between distress alerting devices and search and rescue homing devices. Also there are search and rescue homing devices that employ RADAR.
jimh posted 12-07-2014 07:33 AM ET (US)
More about AIS SART devices can be found at
http://www.navcen.uscg.gov/?pageName=typesAIS
In the subsection AIS Search and Rescue Transmitter (SART) you find this explanation:

quote:
Mobile equipment to assist homing to itself (i.e. life boats, life raft). An AIS SART transmits a text broadcast (message 14) of either 'SART TEST' or 'ACTIVE SART'. When active the unit also transmits a position message (message 1 with a 'Navigation Status' = 14) in a burst of 8 messages once per minute.
AIS SARTs are also used in maritime survivor locating devices (MSLD) or man overboard (MOB) devices, as specified in RTCM 11901.1, Standard for Maritime Survivor Locating Devices as well as for AIS locating beacons on 406 MHz EPIRBs. Standard AIS SARTs can be identified by MMSI's beginning with the numbers "970", AIS maritime survivor locating devices or MOBs with MMSIs beginning with "972", and AIS EPIRB with MMSIs beginning with "974". All categories of AIS SARTs will be displayed on IMO-mandated shipboard navigation displays.
jimh posted 12-07-2014 07:46 AM ET (US)
Here is a list of manufacturers who have registered to obtain manufacturer identity codes for making AIS-SART devices:
http://www.cirm.org/services/ais-sart.html
At this moment there are 35 manufacturers registered. If you browse the list you see only two manufacturers registered with addresses in the USA. One of those is ACR Electronics in Florida. Most manufacturers listed are in China.
The other USA manufacturer listed is BriarTek. They do not appear to manufacture any devices. BriarTek does have a patent that covers some aspects of emergency location devices, and appears to be trying to license the patent, rather than actually manufacture and sell devices that use the patent. The patent is in dispute. See
http://www.pressherald.com/2014/06/16/ briartek-patent-key-to-delorme-dispute/
http://www.panbo.com/archives/2013/02/ did_briartek_invent_two-way_distress_beacons.htmlhttp://www.panbo.com/ archives/2013/02/did_briartek_invent_two-way_distress_beacons.html
ASIDE: It is unfortunate that in the USA there seems to be more interest in patents and intimidating competitors with patent law than in actually manufacturing useful devices.
jimh posted 12-10-2014 12:44 PM ET (US)
I tested the response of my chart plotter to a simulated AIS-SART signal. See
http://continuouswave.com/ubb/Forum6/HTML/003687.html
for the details.

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