Automatic Identification Systems

Insequent said:

Couldn't see you on AIS? But dont you have Class A ?

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He had a Class B, but it came out with all the Simrad gear and was replaced by a Class A unit.

Ah, thanks.

Boydski said:

Hi Oliver,

I've heard the same rumors, but my experiences lead me to believe otherwise. I spent a lot of weekends this summer running into and out of Seattle, which is extremely busy with both commercial and recreational traffic.

I have observed on several occasions when I've been involved with complicated crossing situations that large commercial traffic has altered their course based on my AIS class B transmissions (they could not see me via Radar or visually at the time). One particular situation comes to mind that involved 5 vessels having to give way slightly and a tug with tow that was the stand on vessel for the other five. All six vessels did what they were supposed to like a well choreographed dance. It was impressive to watch.

To the OP, I have a Simrad AIS transceiver, which works well for me. It outputs NMEA 0183 and 2000, so the vessel data shows up on the Navigation PC's, the Furuno gear and the Simrad Chartplotters.

Of course, YMMV,

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: thumb:

Exactly my experience.
Also see Kevin's paragraph about working backwards. Decide what you will view it on and go from there.

While I did use Marine Traffic app for two years, I certainly can't see paying for a receiver only set up, when the transceiver only costs $200 more.

My Digital Yacht B class transceiver cost only $580.

On B versus A. I wonder who started the rumor that ships turn off the B?

How does that even make sense? As the little boats who do transmit B are exactly the ones that are hard to see, yet they want to avoid.

In hindsight, unless one spends virtually all their time in the ICW, The ais transceiver should have been one of my first purchases.

My average ship encounter distance went from collision course to greater then 3 nm, and normally greater than 5nm.

Nsail said:

And, what about Canadian VTS - do they monitor both Class A and Class B?

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Yes. In Straits of JDF both US and Canada appear to monitor B, so am curious about Seattle VTS.

Class B has a less frequent transmit cycle than A. B does not give you a real time image like radar. Not uncommon for an 1/8 to 1/4 mile separation if target vessel is moving at 30 knots.

Sometimes sport fishing charter vessels turn off AIS in Alaska as they get paranoid about sharing fishing grounds.

sunchaser said:

Yes. In Straits of JDF both US and Canada appear to monitor B, so am curious about Seattle VTS.

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That was not my experience in October 2014. I checked in with JDF VTS and told them where they would see me on AIS. They couldn't see me and asked if I had Class B, which I did at the time. They said they do not receive Class B. This is first hand. I subsequently overhead the same conversation with other boats that had Class B.

Now keep in mind that I'm talking about VTS, not about the various boats out there. I expect they CAN see Class B. I think only pretty old, first-generation AIS devices don't receive both.

The Puget Sound VTS, puts out a user guide in PDF.

Juse read through it and it said no "B" tracking....

But just cause it's online...not fact as it may have not been updated or could be in error....could always call if really interested.

Finally the thread begins to get it right. Class A and B work exactly the same except class A is refreshed in a way to not miss another transmitting AIS as often as the Class B might. The difference in AIS to most of us Leisure/recreation boaters is whether the AIS is a receiver only or a transceiver. Clearly it is a nice improvement to have a transceiver and let others see you than to only have a receiver that lets you see others but they can't see you. Most Transceivers including mine have a no transmit switch. I can turn my transmitting off, go figure as to why I would want to do that. I say most bang for the buck is a Class B transceiver. I paid $500 for mine at West Marine.

Since an AIS that transmits... first transmits whether it is a class A or B, traffic folks that are looking only at commercial traffic can and do often set their receivers to not track class B AIS. This is why you are sometimes warned that class B units are not tracked. It is not because they can't see them its because they are not concerned with them, and are literally not tracking them. If traffic folks set their receivers to not see class B then they can't see them.

I'd be real interested to see an example of a receiver that has a "don't receive Class B" switch on it. So far I haven't seen one.

As for VTS in the greater Puget Sound, all I can really say is what my interaction was with them. It was pretty clear that whatever display they were using to see boats did not display Class B devices. For me and a few other boats transiting the area, their words were "we can't see Class B AIS", not something like "oh, I see you are class B, we won't track you". Actually, just the opposite. They did track us and asked us to check in at various points long the way.

Wxx3 said:

: thumb: On B versus A. I wonder who started the rumor that ships turn off the B? .

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Not necessarily a rumor. Panbo has a very long thread on realities vs myth of Class B filtering by large ships as started by the AIS expert - Norris.

On a side note, Class A has a "refresh" rate of 2 to 10 seconds and class B 30 to 180 seconds dependent upon target distance. So best we keep our radars on and in good working order as Class B AIS is only a good but not perfect tool in snotty weather close encounters.

Class A and B described below by the Coast Guard. They are the same except in performance. Please note that class B is interoperable with all other AIS stations

TYPES OF AUTOMATIC IDENTIFICATION SYSTEMS (PER ITU-R M.1371 AND IEC STANDARDS)

Class A | IEC 61993-2

Shipborne mobile equipment intended to meet the performance standards and carriage requirements adopted by IMO. Class A stations report their position (message 1/2/3) autonomously every 2-10 seconds dependent on the vessel’s speed and/or course changes (every three minutes or less when at anchor or moored); and, the vessel’s static and voyage related information (message 5) every 6 minutes. Class A stations are also capable of text messaging safety related information (message 6/8) and AIS Application Specific Messages (message 6,8,25,26), such as meteorological and hydrological data, electronic Broadcast Notice to Mariners, and other marine safety information (see IMO Safety of Navigation Circular 289, GUIDANCE ON THE USE OF AIS APPLICATION-SPECIFIC MESSAGES (ASM) or the IALA Application Specific Message Collection).

Class B | IEC 62287-1 and 62287-2

Shipborne mobile equipment which is interoperable with all other AIS stations, but, does not meet all the performance standards adopted by IMO. Similar to Class A stations, they report every three minutes or less when at anchor or moored, but, their position (message 6/8) is reported less often and at a lower power. Likewise, they report the vessel’s static data (message 18/24) every 6 minutes, but, not any voyage related information. They can receive safety related text and application specific messages, but, cannot transmit them. There are two types of Class B AIS, those using carrier sense Time-Division Multiple Access (CS-TDMA) technology and those like the Class A using Self-Organizing Time-Division Multiple Access Technology (SO-TDMA). Class B/SO is generally more capable; Class B/CS is generally less expensive. See this broader comparison of Class A and Class B AIS.

twistedtree said:

They did track us and asked us to check in at various points long the way.

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Our experience in the Canadian west coast VTS areas is that when weather is bad we are not controlled per se but contacted by VTS as to our intentions when in the midst of VTS controlled traffic.

In Alaska's less than clear weather the overtaking cruise ships and tugs ask our intentions or to maintain course as they pass us since our B AIS sends out delayed signals and the taller ship's radar loses us as they get close.

Class B filtering is real.

SetSail » Blog Archive » Class B AIS Filtering – The “Myth” Is Real

sunchaser said:

Not necessarily a rumor. Panbo has a very long thread on realities vs myth of Class B filtering by large ships as started by the AIS expert - Norris.

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Yes, and I believe the conclusion was that it was not true. The Furuno FAR2xx7 radars have a filter selection for Class B AIS targets, adn that would lead one to believe you can shut them off. But one of the people in that thread clarified that it actually does something different like stopping them from alarming, but it doens't stop displaying them, but I can't remember. In installing one of those Radars shortly, so will soon be able to say for certain.

But since then Puget sound VTS told me directly that they do not see Class B, and I discovered that my very our charting system, Coastal Explorer, also have a filter check box to turn off Class B targets. But I know of no other examples, and I've asked many times. If anyone has some, I'd love to hear them.

obthomas said:

Class B filtering is real.

SetSail » Blog Archive » Class B AIS Filtering – The “Myth” Is Real

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I find NOTHING definitive in that thread. Just more speculation by people who DO NOT know how the radar in question (Furuno FAR2xx7) actually operates, and they even admit it.

Is the article putting words in these folks mouths?

There is both a vessel size and AIS B filter, which when activated will filter out targets. This is confirmed by Furuno and Dr. Norris, one of the AIS fathers.

Q: Can vessels with AIS devices filter out Class B AIS?
A: In some cases yes. Some vessels will "filter" the display so that Class B targets don't show up. Keep this in mind and don't always assume you will be seen by other vessels with AIS equipment.

Class B AIS FAQs

obthomas said:

Is the article putting words in these folks mouths?

There is both a vessel size and AIS B filter, which when activated will filter out targets. This is confirmed by Furuno and Dr. Norris, one of the AIS fathers.

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It's not clear what radar or other AIS display device Steve is referring to in that statement, though it's presumably the previously referenced FAR2xx7. But the way the radar apparently actually works is a bit different based on details that Ben dug up. So I don't believe Steve's statement is definitive, which was my point.

I'm not saying he's wrong or that he's right. I'm just saying I haven't seen a definitive answer to the question. I too have raised this particular device as a possible example of one that in one way or another handles Class B targets differently than A.

What I'm looking for and what I think would be helpful are clear examples of devices that "ignore" Class B in some way, with details on what they actually do.

I think one thing we all need to keep in mind is that a commercial ship captain has his license and career on the line when he's operating a ship. To come into a port and turn off potentially valuable navigational information seems nuts. How would you explain that to a court after you flatten one of those Class B targets that you turned off?

obthomas said:

Q: Can vessels with AIS devices filter out Class B AIS?
A: In some cases yes. Some vessels will "filter" the display so that Class B targets don't show up. Keep this in mind and don't always assume you will be seen by other vessels with AIS equipment.

Class B AIS FAQs

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Again, I'm not agreeing or disagreeing. I'm just looking for concrete examples that will stop swirl of repeated "I heards".

Here is an extract from my Simrad NX-40 Navstation manual. It appears I can filter out vessels, but not by Class A or B. With a little effort you can probably filter out most Class B transponders by deselecting different vessel 'types'. Obviously this functionality will be different for different plotters etc..

twistedtree said:

...

I think one thing we all need to keep in mind is that a commercial ship captain has his license and career on the line when he's operating a ship. To come into a port and turn off potentially valuable navigational information seems nuts. How would you explain that to a court after you flatten one of those Class B targets that you turned off?

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Exactly.
Or on the high seas for that matter.

Washington State and Canadian Ferries

Now that the VTS monitoring of Class B AIS has been somewhat clarified, what about Washington State Ferries and Canadian Ferries?

Does anybody know if they monitor Class B AIS?

I installed the Icon unit prior to my most recent trip to Cuba and D.R. as I was single handling the boat I considered it a necessity. I installed it as a stand alone device and did not take the time to connect to chart plotter or radar (it had its own small scaled screen). It was a great investment in open waters w/its rather loud "collision alarm" at five miles. Continuously had to silence alarm as I got into more congested waters or harbors. The COG and SOG of the other vessel being available saved a great deal of radar plotting time. Don't know how I did without it before. Good investment, only draw back was having to place the transmitting antenna in a location apart from my others.

GreenSailor said:

I've been looking at AIS systems and would like to get feed back on the pros and cons of the system. And which ones work the best.

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I don't believe there are any cons to having an AIS outside of cost if one is boating on a tight budget.

I think there can be a case made as to whether or not one really needs it but that's a different question than the pros and cons of the system itself.

About once or twice a year my wife and I have a discussion about whether or not AIS would add anything to our boating given where we boat now and anticipate boating in the future as far as the PNW and BC coast are concerned, and so far the conclusion we have come to every time is no.

We have yet to encounter a situation where AIS would have given us any information we needed that we could not already obtain with the systems we have now (and we boat in the fog when it's foggy). Virtually all the other boaters we know in this region well enough to know how they operate their boats, power and sail, do not have AIS, either, and have not felt the need for it.

Whether one sees value in it for the kind of boating one does is a totally individual thing. I don't think blanket statements like "You're nuts if you operate a boat without having AIS" are valid and I don't believe that newcomers to boating should feel that if they don't have AIS they will be run over and die the first time they leave the dock.

Will we ever put AIS in our PNW boat? Hard to say. But for now and in the forseeable future, we don't see any advantage for us in this region.

But it's a great tool with no downside that we can think of.

Over time I've noticed more and more Class Bs operated in the Bay Area. Most are docked/moored. On occasion I've seen them on land or highway.

One other note on AIS: While your radar will pick up the Coast Guard Cutters your AIS will not. They don't necessarily share their information, yet I am confident that they had mine.

I sailed to Mexico twice, before AIS was generally available. When we started looking at boats again I found out about AIS in small boats and was blown away. Just like I was with chart plotters when they first became available. But Magellan didn't have any of this stuff and you don't "NEED" it either. But it is so much more convenient.

I don't need it. In theory, I don't need anything but a chart, compass and clock.

That said, I made the decision to invest in AIS after several VHF exchanges with commercial traffic in the fog. They asked if I had AIS. It seemed that checking radar, or exchanging info on location, heading and speed, was "plan B". AIS was the preferred method of avoiding other traffic.

Another factor was that I can show my friends and relatives how to use the tracking web sites, and we don't need to call and tell them all where we are as often.

ulysses said:

One other note on AIS: While your radar will pick up the Coast Guard Cutters your AIS will not. They don't necessarily share their information, yet I am confident that they had mine.

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Saw one coming up the Columbia River today and I picked them up, but then again they were not on a mission.

I just installed a Raymarine AIS 650 transciever. Straight forward on the install. I chose Raymarine becuase it intergrates with my new multi function display.

CaptTom said:

I don't need it. In theory, I don't need anything but a chart, compass and clock.

That said, I made the decision to invest in AIS after several VHF exchanges with commercial traffic in the fog. They asked if I had AIS. It seemed that checking radar, or exchanging info on location, heading and speed, was "plan B". AIS was the preferred method of avoiding other traffic.

Another factor was that I can show my friends and relatives how to use the tracking web sites, and we don't need to call and tell them all where we are as often.

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Exactly.

Simply put, in 3,000 nm without it (up, down and up the east coast) & 3,000 with it (across the North Atlantic), it was the best $600 I ever spent.

My close encounters with big ships and ferries simply stopped.

Yes, Marin is right, I clearly didn't get run down when I didn't have it, but there were numerous occasions I had to change course.

With it, THEY changed course to keep me 5 nm away. Without fail!

It adds an extra level of safety.

Lastly, far more small boaters have been killed by getting run over, than have ever been sunk by the proverbial container, that everyone is afraid of, but no one has ever seen.