Panbo

AIS SOLAS-style, Class B is NOT ignorable!

... written for Panbo by Ben Ellison and posted on Apr 7, 2009
IEC62238_IMO_SOLAS_Radar_performance requirements_courtesy_IEC.jpg

Thanks to an angelic Panbot, I've now read pertinent sections of IEC 62388, a.k.a. "Maritime navigation and radiocommunication equipment and systems - Shipborne radar - Performance requirements, methods of testing and required test results." It's a hundred pages (preview PDF here) laying out in great detail the minimum requirements for how all new radars going on SOLAS ships will perform and present data.  Perhaps most important among many mandated enhancements is the treatment of AIS targets, Class B included, putting them on essentially the same level of safety value as radar targets.  I think these standards are good news not only for the bridge teams on big ships, but also us little guys who sometimes travel amongst them (despite the consternation that came up yesterday)...

To appreciate IEC 62388, it's important to understand the state of AIS plotting on ships now. When the IMO mandated Class A AIS on SOLAS vessels the only display requirement was a simple MKD, and a lot of those vessels still have just an MKD.  Today a trawler skipper transiting Chesapeake or San Francisco Bay may very well have better AIS plotting than the ships he or she is seeing on their MFD!  Which may account for the widespread notion that ships don't pay attention to recreational level Class B AIS, along with the persistent myth that they filter out Class B signals altogether (which is impossible, as, by regulation, MKDs must show all AIS targets).

Hallalujah, then, for IEC 62388, which requires that new ship radars be able to track at least 20 "active" AIS targets and 100 "sleeping" ones, as shown in the table above (IEC 62288 apparently has separate, but very similar, requirements for ECDIS).  However, that sleeping/active distinction --- which is mainly just the difference between a small, plain AIS icon and a bigger one with COG, Heading, and ROT vectors shown --- caused a lot of confusion here yesterday, kicked off by a knowledgeable commenter who wrote about how IEC 62388 contains a "REQUIREMENT that the operator be allowed to filter and REMOVE all Class B Targets from the display!!"  Well, let's look closely at that requirement:

10.5.3 Filtering of AIS sleeping targets requirement: To reduce display clutter, a means to filter the presentation of sleeping AIS targets shall be provided, together with an indication of the filter status (for example by target range, CPA/TCPA or AIS target class A/B, etc.). It shall not be possible to remove individual AIS targets from the display. The filter criteria in use shall be readily available.

The bold facing is mine, but I have double checked that such filtering only applies to sleeping targets, and only filters out their screen presentation. Such targets are still tracked because, as we see in the next requirement, they must be made active, and hence present on screen, if they meet certain user defined criteria:
 

10.5.4 Activation and deactivation of AIS targets requirement: A means to activate a sleeping AIS target and to deactivate an activated AIS target shall be provided. If zones for the automatic activation of AIS targets are provided, they shall be the same as for automatic radar target acquisition. In addition, sleeping AIS targets may be automatically activated when meeting user defined parameters (for example target range, CPA/TCPA or AIS target Class A/B). The manufacturer shall state what user defined parameters are available and shall show that they are described in the user manual.

Here my boldface emphasizes how all AIS targets are treated much like ARPA radar targets, a philosophy seen throughout IEC 62388.  And that's a big deal, as suggested by the Radar and ARPA Manual, partially available on Google books.  In conclusion, then, the IMO and other safety organizations involved in the new radar regulations did NOT intend ships to ignore Class B AIS targets in a dangerous way, and did make it easy to do so.  In fact, the new radars should make it much easier for ships to monitor a small Class B equipped vessel, even if it's a poor radar target.  Keep in mind, though, that it will be many years before all ships carry radars like this. 

PS 12/28/2010: I've learned that these IEC regs are looser than I realized.

IEC62238_AIS_Target_States_courtesy_IEC.jpg

Comments

I figure that this will be similar to radar, radio, etc. That watchkeeping is mandated to be with ALL means at the ship's disposal. If you have radar, you're supposed to be using it. The same will probably be true for AIS. And if there is a collision with a boat that's transmitting Class B data and you have class B filtered out, you'll probably be in trouble and at least partially responsible.

Posted by: Anonymous Coward at April 7, 2009 6:07 PM | Reply

I read this a bit differently.

First, it's clearly OK to filter class B targets that are "sleeping". So they are gone.

If you have zone defined for AIS (which is optional), A/B are the same and zone should match ARPA zone.

You also may activate additional targets (such as all class A) while ignoring other targets (such as class B) outside any such optional zone.

This is not a bad solution.

You can optionally set a guard zone matching ARPA, and then filter all Class B outside that zone while leaving Class A and TTCA etc.

Posted by: JohnD at April 7, 2009 6:35 PM | Reply

Ben wrote: "Let's face facts, large ships have routinely assumed that small boats will get out of their way. I assume the filter class B option foster this assumption."

Certainly in most harbors the COLREGS give the right of way to the large ships because they have limited ability to maneuver.

In open water, I always play defense, how can I stay out of their way, unless they explicitly tell me they are avoiding me. The later is happening more frequently as I'm able to communicate with the bridge of the large ship by name.

I think the regulations are irrelevant, Relying on your AIS B to ensure that a large ship won't run you over is like assuming that since pedestrians have the right of way you can freely step into auto traffic. As the saying goes, you could be "dead right".

Posted by: Russ at April 7, 2009 8:19 PM | Reply

The debate about the extremes is always fun, but it will never end. On one end: big ships will turn off class B targets (and run you over). On the other end: big ships have the right of way and probably can't avoid you anyway. I think there is a happier middle way. If you have AIS and if your course is not erratic, then big ships would be able to see you far sooner, when avoiding you (if necessary) is a minor change of course and not an emergency change of course. If they know you are there they can look out for you as they pass. If they don't know you're there, you might be swimming watching them sail away. Give them a chance (and hope they take it).

Imagine a pedestrian wearing black, at night, with no reflectors. Something I would rather avoid if I can.

Posted by: norse at April 7, 2009 11:40 PM | Reply

Norse wrote. "Imagine a pedestrian wearing black, at night, with no reflectors"

You mean a fiberglass boat with no radar reflector ... not hard to imagine, I see them all the time.

The large bulky radar reflectors that actually work (RCS => 10), are a rare sighting on boats in my harbor.

Posted by: Dan Corcoran (b393capt) at April 8, 2009 6:35 AM | Reply

Great post Ben ... I enjoyed the level of detail and relevance your bring to these documents in making your point, quite succesfully, the state of AIS plotting on ships.

I am amazed at how much thought went into / how sophisticated and technical this AIS filtering has been considered in the world of safety regulation.

Again, great post !

Posted by: Dan Corcoran (b393capt) at April 8, 2009 7:25 AM | Reply

With growing interest I followed the discussion on AIS Class B stations and the display of it. What is the difference of displaying radar targets or AIS targets? There are the same number of them. Problem is that most users want to see everything, even when it is not needed. In radar you see just a target, with AIS you can see a target but also a lot more. It is up to the user to decide what he wants to see, just the target (a symbol for AIS) or all additional information. The user must learn to display additional information only when he/she it needs for the safety of navigation. The name and MMSI and destination and dimensions are absolutely irrelevant for the most ships. Only in the situation that you need to contact a ship, or when you need to know the course and speed information from the other, you can point to the target and will get the information you need. And the rest, leave it to a target!

Class B is designed as a self regulating system within AIS. As soon as there are too many Class B stations in the air in a limited area, the system will reduce the number of reportings. Also in a VTS environment there are tools to reduce the cluttering on a radar screen. However, this will only be needed when really a great number (more than 100) of Class B equipped ships are on a limited area, e.g. during a sailing event or something.

The purpose of installing an AIS Class B is safety. You have a better chance to be seen and you will get a better overview of the traffic situation. Better than radar can do and as an extra the identification is given. In radar you will see targets, AIS gives them a face! And it will be the user to decide that the Class B can improve the safety, both of himself but also for others. In particular during the night or bad weather conditions. And I am not speaking of a port situation or restricted waters but at open sea where you do not have an overload of the AIS link nor an overload of your display. In situations where an overload can occur there is only one very important means to improve the safety: LOOK-OUT and handle as appropriate. Don't trust on any electronic mean when you are with say fifty ships on a small area, to avoid missing the one on your collision course.
AIS will improve safety but use it with care!

Wim van der Heijden
Chair of the IALA AIS group

Posted by: Wim van der Heijden at April 8, 2009 5:04 PM | Reply

While I generally agree with Wim van der Heijden, I think he is making an unwarranted assumption that a boat will show up as a target even if AIS filters out class B. Note that some of the folks with AIS B transponders have them precisely because they are worried with good reason about whether their boat will be picked up on radar under certain wave and weather conditions given less than perfect radar reflectors and low boats and non-reflective build materials like fiberglass. If any doubt is raised about AIS visibility on radar, you are going to see such folks move to active radar transponders which probably are less useful to the other crew.

Posted by: Anonymous at April 8, 2009 6:09 PM | Reply

We all seem to be spring-loaded to the alarm position about AIS-B clutter, but I wonder. My 5 watt handheld VHF is good for 6 miles range on a good day. How much ocean is my 2 watt AIS-B going to "pollute" if the antenna isn't any higher? How about if the antenna is 50' high? Is it safe to suppose that a typical SOLAS vessel with AIS A has an antenna perhaps 120' above the water? How far away is he going to hear me coherently? Finally, how many Class B AISs can we expect to see in that range of reception?

My argument is this: Two thirds of the vessels who would acquire AIS B radios are power boats. Their antennas would not be more than 30' above the water. The remaining one third are sailboats, predominantly sloop rigged and reluctant to replace a masthead VHF antenna with an AIS antenna, so perhaps only one sixth of the potential market for these radios are either multi masted or have antenna switches which would permit an antenna height of 50 or more feet above the water. These numbers are no longer threatening.

Posted by: Sandy at April 8, 2009 9:19 PM | Reply

I run a 90' Yacht and installed a "B" AIS from Furuno. I have had it running now for a few months and am very interested in seeing the view from the "big guys" bridge. I have zero intention of pushing my right of way over any commercial ship over 50m, ever. The main use for me with the AIS has been to see targets when my radar does not pick them up. This has happened many times in rain where I can get a radar target at 4 miles but see the AIS at 12. I still rely on ARPA to judge collisions but the AIS is just one more tool. I am constantly told that no one can read my name or info just my number and I don't know if this is a result of me installing a Furuno B instead of an A AIS? I was told that newer AIS units would read the B but I don't know. It may be my particular unit but I'm not real happy with the Furuno AIS at all for this reason. I for one would be thrilled to pick up ANY AIS target in front of me no matter how small the vessel and I plan on having no collisions at sea as I hear they ruin your day. I wanted an A but since the vessel was not mandatory I put this on instead as it is much cheaper but perhaps not worth it if you really want to be noticed according to what I read here.


Posted by: Capt Tedd Greenwald at September 26, 2009 7:40 PM | Reply

Capt. Tedd,
The receiving units on other vessels are the problem and require firmware updates to read complete Class "B" information. So, the older or less well-maintained the receiver, the less Class "B" information interpreted. Unless the vendor programmed your AIS incorrectly, your vessel's name is in there. You are responsible for dimensional data in meters and type as I understand it.

Posted by: Ron Rogers at September 27, 2009 12:53 PM | Reply

Tedd, The problem is not your Furuno Class B transponder but rather the Class A transponders on the ships that are only seeing your target and MMSI#, not your vessel name, type, call sign, and dimensions. The software in those transponders needs to be updated to understand the Class B "static data" message which was changed after many of the original Class A transponders were manufactured and installed.

This situation WILL improve. As Class B transponders proliferate, the ships are realizing they need the update. Plus the USCG plans to push better AIS implementations:

http://www.panbo.com/archives/2008/12/ais_mandates_in_the_usa_the_coast_guard_speaketh.html

Posted by: Ben at September 27, 2009 12:56 PM | Reply

Ron and Ben, thanks for the input. I have replaced my VHF antenna for AIS now for the third time and it seems to be working and I have been told that my name is out there now. My concern was from official vessels and canal control operations that my Name was not seen. I was particularly concerned when following a USCG cutter up the Hudson and they call me to relay that they can't read my name so that is what started my concerns. When I got to the Welland Canal the canal control there did not pick me up either. So it's hit and miss having B full info picked up. So if it is in the budget an A would be a better choice. But the fact that I am seen at all is of some comfort. I transit Lake Erie tomorrow and I'm very glad to have the AIS working well now. Always keep the land in sight and never ever sail at night.

Capt Tedd Greenwald
Yacht Go Fourth

Posted by: Tedd Greenwald at September 29, 2009 7:47 PM | Reply

I have been cruising with AIS extensively for over a year and while I do think it is a great improvement in safety, I fear that too few users realize its limitations. Class "B" users are likely to be lulled into a false sense of security. If it only transmits at 2 watts then it really isn't going to help big fast ships avoid you.

Just a few points and questions to avoid making this a long dissertation.

1> AIS shows the tug, but not the barges. In the Pacific Northwest it is not uncommon for the barges to be 1/4 to 1/2 mile behind the tug. Pleasure boats have to cross shipping lanes at as close to 90 degrees as possible. Somebody dies here every year by crossing over the tow line.

2> I have already talked to enthuiastic AIS users who say that they now pass much closer in bad weather because they trust the AIS tells them where the ship is headed. Experienced users know that AIS shows where the boat is pointing at a certain moment in time, but not where it intends to go. Ferries make a lot of course changes.

3> I have found a lot of targets where the AIS position is different than what radar shows. Sometimes the difference is quite large -- GPS has limitations. Users must remember that AIS relies upon the quality of the other guy's electronics installation. This is going to be an even bigger problem for Class "B" targets. I recently followed one class "A" with an AIS signal that showed him on the opposite side of the channel from where he really was! (There were overhead powerlines that may have messed up his GPS position.)

4> Heading information is frequently off or disappears at inopportune times. Joe the tugboat may not have the latest heading sensor technology. This is subtle enough that you might not notice it unless you plot the target's course on radar. This will be really bad for class "B" targets since we have no requirement for accurate heading sensors.

5> I find myself becoming complacent about looking for large fast vessels because I assume that large boats (eg Cruise ships) will show up on AIS well before I have to worry about them. But I found one cruise ship in Johnstone Strait that had no AIS signal at all! Some military ships do not show up on AIS. If we start using AIS in preference to radar because we assume that everybody has class "B" we will have collisions.

6> I find myself getting lulled into going too close to large targets when I have the GPS/Radar/AIS screen zoomed in. The ferry out the window suddenly looks a lot closer than the ferry on the screen. This is a danger with radar as well, but for some reason I catch myself doing it more often with AIS.

7> One of the most useful things about AIS is that it lets me know when I have the radar mistuned. If I see a target with no return it is time to change the settings.

8> Is it really true that AIS Class "B" is 2 watts? What is the typical range at 2 watts?

I think that we will have a number of "AIS assisted accidents", at least until people get used to the limitations. I really am concerned that people will use AIS in lieu of radar, and that would actually be worse than having nothing at all.

George

Posted by: Orcas George at September 30, 2009 12:58 AM | Reply

Oy. Apparently Furuno has enabled the IMO's sleeping target filtering concept on its big radars, and the menu has led Steve Dashew to think it possible to ignore Class B targets, or even other Class A targets below a set length:

http://setsail.com/ais-a-or-b-a-disturbing-discovery/

Today I'll try to find out exactly what tat AIS Filtering menu means, but here's guessing that it only applies to sleeping targets and does not effect the tracking of any particular class of target or display of dangerous ones. (Thanks to BrianM for a head's up on this.)

Posted by: Ben at December 15, 2010 8:40 AM | Reply

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