"A" versus "B" AIS - worth transmitting?

[Chuck Hawley]

Originally Posted by rsn48

So my somewhat limited knowledge based on a shaky foundation is that there are two classes of AIS - A and B. Commercial and large vessels use A and the rest of us use B.

The issue of larger vessels filtering our Class B signals has been sort of a depressing vapor around the use of Class B AIS. While I believe it is possible on ship-based AIS, I don't think the option is a common one unless, as some have suggested, the number of targets is overwhelming in an area of high traffic density.

What's missing from this discussion is a mention of the newer Class B transceivers which generally go under the name of Class B-SO or SOTDMA (SO = Self Organizing). These transceivers share the "smarts" of the Class A units, and are therefore allowed to transmit at greater power and more frequently than the original Class B-CS units (CS = Carrier Sense).

See the Coast Guard site for a comparison.

What I can't answer is whether the ability of a Class A unit to ignore the signal of a Class B includes these new, smarter Class B-SO models. Is there a hierarchy of ignoring other vessels? Don't know.

What is clear, I think, to anyone who has cruised with and without AIS on a crowded coast, is that AIS reception is an enormous improvement to the safety of vessel operators, and it's made incrementally better by being an AIS transmitter. That, in turn, is made better by using AIS that is more and more capable and powerful. If I were outfitting a boat now, there's no question that I would opt for the more expensive Class B-SO option. Based on my experience with marine electronics manufacturers, I'd probably get this one.

Chuck

[CarlF]

I’ve really lost patience with the folks who are too cheap or too stuck in the past to install an AIS transciever.

Money is not a good excuse now that transceivers are under $500 - easily paid for by a few nights of anchoring out instead of taking a slip or slowing down a bit and burning less fuel.

The “recieve only” folks are the most agravating. They’re happy to use my AIS signal to make THEIR navigation easier but refuse to do the same for me by transmitting AIS. It’s inconsiderate - like not slowing down and giving me a huge wake when passing.

I’ve taken to hailing boats offshore that look like they can easily afford AIS with “Captain, you might want to check your AIS, it doesn’t seem to be transmitting”

[boat driver]

to clarify a couple comments-
The Class A transceivers are designed to filter out class B in event the system overloads and/or on some units the operator thru the menu may opt to filter out B if the area is to crowded. That said, the situation of filtering out from airwave congestion is very rare- the system is equipped to handle approx 2400 AIS transmitters at a time.
The intentional filtering out of AIS B is rarely done and only for a specific area. The previous comment about the Galveston VTS and Houston Ship Channel sounds dubious as a widespread practice vs a reception issue. 1) the VTS is an USCG run safety provider- so does not make sense 2) the Houston ship channel has a number of local commercial vessels that operate on AIS B and so this would be counterproductive.
As far as AIS B or AIS A- that is a personal, economical, and power supply decision.
Most small vessels do not need 12.5 watts distance, they do not want to spend $3K up , and they do not have the battery power for the higher unit.
As a safety device- it is really worth the expense and do not waste the money only going half way. Get the transceiver

[Paul L]

Originally Posted by carioca

The Houston/Galveston VTS only picks up Class A AIS. Many large commercial vessels transiting the Houston Ship Channel will turn off the reception of Class B signals.

Filtering targets to reduce clutter on AIS or ARPA displays makes sense when needed. Blindly filtering all Class B seems pretty unlikely.

[guyrj33]

Originally Posted by CarlF

I’ve really lost patience with the folks who are too cheap or too stuck in the past to install an AIS transciever.

Money is not a good excuse now that transceivers are under $500 - easily paid for by a few nights of anchoring out instead of taking a slip or slowing down a bit and burning less fuel.

The “recieve only” folks are the most agravating. They’re happy to use my AIS signal to make THEIR navigation easier but refuse to do the same for me by transmitting AIS. It’s inconsiderate - like not slowing down and giving me a huge wake when passing.

I’ve taken to hailing boats offshore that look like they can easily afford AIS with “Captain, you might want to check your AIS, it doesn’t seem to be transmitting”

Wow what an incredibly intolerant attitude.

[Dockhead]

Originally Posted by Noisykate

FWIW: another vote definitely in favour of transmit. The only place we turned ours off in 5 years was in the river Hamble, off the Solent - alarm was on constantly because of the density of traffic. As I understand it, a big ship will only filter out class b transmissions for the same reason - alarms going off constantly, warning of traffic which is -say- actually outside the shipping channel.

You don't need to filter out targets to solve the alarm problem. You just need to adjust the alarm parameters correctly for the circumstances. Which means alarms OFF in many crowded harbours. Not AIS off.

[Pizzazz]

I agree that AIS is super helpful both in crowded harbors and ocean crossings. However, 1) it is an aid to safe navigation and 2) the user interface on most chartplotters is very hard to use.

I think small vessels have no need for class A transmit at all as it is unfair to expect a large ship to alter course for a small sailboat (I just completed the ARC and can tell you that you cannot expect a large tanker or a container ship to alter course for you, even if you have the right of way, even if you tell them on VHF that you have the chute up. Some are polite, some yell at you.). Next, small vessels are not required to transmit so you cannot count on all of them transmitting. Racing boats do not (you can figure out when they gybe), fishing boats do not and military ships obviously play tricks.

If you want to be seen, carry a good size radar reflector. If you want extra security, then transmit B, but if you are a small vessel (say a 12V system vs 24V) do not transmit A. It is not designed for you.

SV Pizzazz

[Dockhead]

Originally Posted by billknny

There are very good reasons that AIS was divided into two classes. It was to keep un-necessary traffic in busy areas to a manageable level. There is only so much bandwidth available. If every little boat had a Class A AIS the whole system would collapse if every boat was broadcasting on higher power and more frequent updates.

In a truly logical world, Class a transmitters would not be allowed on Recreational vessels below a certain size.

The idea that "I want a Class A so the big ships can see me in a busy harbor" is silly. In those kinds of places they have NO maneuvering room. All they can do is call you on the radio and yell at you to get out of the way. Rule 9 anyone????

In congested, busy waters it is YOUR job to stay clear of the big boys. They can't do it for you. You'll see them on your screen. What more do you want?

In open water it is a different story, and the Class B transmitter gives you everything you need.

Class B is a lot better suited to short handed recreational vessels. Class A has voyage data which has to be programmed before every time you go out. It also has nav status, unlike Class B, which means you have to switch between "Under Sail" and "Motoring" every time that changes (also "Anchored" and "Moored").

Do you have enough crew to keep a Class A AIS set in the correct data?

[Chotu]

Originally Posted by CarlF

I’ve really lost patience with the folks who are too cheap or too stuck in the past to install an AIS transciever.

Money is not a good excuse now that transceivers are under $500 - easily paid for by a few nights of anchoring out instead of taking a slip or slowing down a bit and burning less fuel.

The “recieve only” folks are the most agravating. They’re happy to use my AIS signal to make THEIR navigation easier but refuse to do the same for me by transmitting AIS. It’s inconsiderate - like not slowing down and giving me a huge wake when passing.

I’ve taken to hailing boats offshore that look like they can easily afford AIS with “Captain, you might want to check your AIS, it doesn’t seem to be transmitting”

No worries. I'm not monitoring my VHF all day long either. Lol

But I do keep a real watch at all times, I do see you and I do abide by all nav rules.

[Comix Bay]

I do think it should be mandatory that AIS should be switched of when tied up in ports/marinas.. the stationary blobs smother to much mobile traffic.[/QUOTE]

My Grandson operates a commercial vessel and his AIS is controlled by the ignition switch. When he turns the key on his AIS is on, when he shuts her down at night the AIS goes down. IMHO this is the way all should be installed.

[Cpt Pat]

I had a Class B AIS on board for 6 years. Recently, I upgraded to a Class A because I came upon one at a good price. The Class A has features you may not use, such as the ability to indicate your nav status: underway sailing, moored, restricted maneuverability, etc. You can also send directed or broadcast safety related messages - essentially text messages, that can appear on the other vessel's navigation display.

I sail in some challenging conditions - I recently came in from 19 foot swells at 21 seconds. I really don't want to find myself abeam to those swells in my 26 foot boat. There's about 90 degrees of arc in heading that is unusable to me in those conditions. Designating your vessel as "restricted in ability to maneuver" is at the skipper's discretion, and in those conditions, setting the AIS navigation status accordingly is useful.

One other nav status you see that cargo ships use all the time in the approaches to San Francisco is "not under command." They shut down and drift while awaiting a scheduled slot for anchorage or mooring, essentially saying: "don't expect me to move because I have no way on." If I ever found myself again hanging from a sea anchor or hove to in the ruff - I'd send the same status. "Stay away. Neptune is at the helm."

If you don't plan to use features like that, then a Class B will do just fine.

My Class B consumed 0.5 amp, and the Class A consumes 0.75 amp.

On the topic of "filtering out" Class B vessels: My Class A transponder has no ability to do that, nor have I heard of any other that does. But the navigation displays could conceivably be set to "declutter" like that. It would be very poor seamanship since there's no mention of a "rule of tonnage" in the navigation rules. On the other hand, my Vesper AIS display does filter out any vessel (Class A or B) that is not a potential collision hazard, greatly reducing the clutter. Vessels that leave their AIS on all the time are not a "clutter" problem for anyone who has such an intelligent display. And channel congestion isn't an issue: the AIS channels will support over 2,000 stations within line of sight.

As far as I know, all Class A and Class B transponders have the ability to disable transmission. We don't have a piracy problem here, so I never connected that feature to a switch.

The only "downside", if you interpret it that way, is the increased likelihood the Coast Guard will call you out of the blue asking you to assist in a search and rescue. I don't mind - it's the Law of Sea to assist. It's happened to me twice.

[rsn48]

Comix Bay, it is my impression that most small boats in around Comox, the Islands close like Pender, Hornby, Texada and Lund and north, don't have AIS. I know many do, what is your experience?

[CaptTom]

Folks not maintaining a listening watch on VHF, or declaring themselves "RAM" even when they're not restricted by the nature of their work...

Sigh.

[Cpt Pat]

Originally Posted by CarlF

The “recieve only” folks are the most agravating. They’re happy to use my AIS signal to make THEIR navigation easier but refuse to do the same for me by transmitting AIS. It’s inconsiderate - like not slowing down and giving me a huge wake when passing.

Not to be competitive, but I think I can "one up you" on the aggravation scale: WAFIs (wind-assisted floating idiots) who use Marine Traffic on their smartphones for traffic avoidance.

Marine Traffic itself warns people not to do that because positions are not real time and are dependent entirely on volunteer receiving stations (I run of those stations myself) that are subject to all of the reliability issues of posting those reports over the Internet all the way back to their servers in Greece. And the reports that do make it down the pipe to Greece are often delayed by several minutes.

Those skippers think they're safer -- while they are being lured by smartphone sirens to the "rocks" (under a tanker) by a false sense of security. Marine Traffic is intended for the sport of "boat spotting" -- not for traffic avoidance!


Here near Silicon Valley, the capitol of Geekdom, I see them all the time glued to their smartphone, feeding their addiction, and trying to spot traffic while underway via the Internet. And I've heard: "Hey, is your AIS working? I didn't see you on Marine Traffic coming into the harbor?" That's because you don't have an actual AIS receiver (you tech-addicted moron), and when I'm sailing, there is no coverage on Marine Traffic for 10 miles around because mine is the only AIS receiver feeding Marine Traffic in this harbor - which is off the Internet when I'm underway.


Do I sound aggravated?

[Cpt Pat]

Originally Posted by CaptTom

Folks not maintaining a listening watch on VHF, or declaring themselves "RAM" even when they're not restricted by the nature of their work...

Sigh.

It has nothing to do with "nature of the work." RAM regards maneuverability. And it's only fair to let vessels around me know that: no I'm not going to adopt a heading that will roll my vessel in these swells.

Read the International Navigation Rules for the definition of RAM.

Feel free to stay silent yourself, I was trained to communicate my navigation status when it may affect other vessels.


RAM is a designation that I use only in extremis, as an AIS equivalent of a sécurité call. Licensed professional mariners: people who actually had to pass the USCG Rules of the Road written test, understand its meaning: "there are courses I cannot adopt." It's a prompt to make a radio call to arrange a crossing. It's those large vessels that have the ability to even see my AIS navigation status on their navigation display that concern me. For your vessel, we'd probably just exchange paint in a collision.