Class B AIS filtering, a “meme”?

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

32 Responses

  1. Tacophan says:

    Racon buoys in the S52 presentation have a magenta ring around them. The actual properties of the racon signal can be found by query of the buoy. Not as conspicuous as a raster, but if you know what to look for it is there.

  2. Eric says:

    I saw the same article and was aggravated at the assumption that Class B filtering would take place–routinely even! I think the situation will be similar to radar. If you have it but aren’t using it and you have a collision, you’re likely to have to accept all or some of the blame. Can’t remember the exact wording, but the Colregs specify that watchkeepers must use all means at their disposal. I would think there’d be severe consequences for a big boat with Class B filtered out which collides with a little boat which is transponding.

  3. Jak says:

    I spoke to a sales guy from Rose Point a year ago. He said the first feature request they got after adding AIS tracking was a filter for class B.
    Personally, I think it is crazy. We shouldn’t have to have somebody in a small craft die before this attitude is legislated away.
    What we may need is some intelligent filtering based on speed of approach or time to collision. If the display is unreadable due to too much data, then there are known techniques in the user interface world to fix it.

  4. Captain Jack says:

    I spoke with the Rose Point president and he said there will be no support for the Mac OS or the iPhone. I prefer Apple Macintosh over Windows Vista for it’s easier to use. Meaning that I don’t have the driver issues I had with Vista. Also on the Mac I don’t have to deal with viruses and anti-virus software that keep warning me all the time. I’m seeing more yacht using Macs on board and iPhones than I have ever before.
    So I very well see this craziness with Rose Point about adding AIS tracking filter for class B. Crazy is what crazy does. šŸ™‚

  5. tacophan says:

    One of the issues is that these ECS systems are not type-approved or have any standards of quality attached to them. (So far ECDIS is the only standard) Thus you get commercial vessels sailing with systems that can arbitrarily remove navigation-critical data from the display. Just be thankful the airlines aren’t run like this…

  6. Russ says:

    That’s the first I’ve heard of a ship hailing a small boat by name. Very encouraging!

  7. Ben Ellison Ben Ellison says:

    Criminy! It was pointed out to me (and I confirmed) that Fugawi Marine ENC has an “Ignore Class B” option just like Coastal Explorer’s! And apparently Nobeltec let’s users filter out AIS targets based on vessel types like “tanker” and “freighter”, which could be used to ignore all Class B’s and more.
    So I’ve been unfair to Coastal Explorer, singling it out as the villain here. My apologies to Rose Point, though I hope everyone understands that my focus on CE mainly reflects how excellent and important I think the program is.
    But learning that Class B filtering is more common than I realized doesn’t help me understand the need for it any better. In fact, it seems weirder. As best I can tell the IMO will not permit ship’s to ignore Class B or any other dangerous targets. But here are charting programs like CE and Fugawi — the very AIS target plotters apt to be on yachts carrying Class B transponders — endorsing the Class B filtering concept.
    Meanwhile I’ve yet to see a screen shot illustrating why Class B targets need to be filtered out (submissions welcome). And I strongly suspect that if we did see such screen shots, we could come up with suggestions about how the targets could be better presented, so as to unclutter a screen but not simply ignore vessels that might cross our path. Again, I think what we’re seeing is a meme at work.

  8. Pascal Goncalves says:

    Hi Ben,
    I do not see a big problem if any software or chart plotter firmware have AIS Class B filtering. I think that, almost all Class B AIS units can turn the transmission of AIS signals OFF at any time the owner wishes. The masters and captains of the ships could do the same thing with this AIS Class A units, as specified in the IMO COLREGS etc. Almost all softwares can filter AIS class B including the “ShipPlotter”. As we can see, everything depends on the circunstances and the captain decisions. Sorry the bad english.
    Best regards

  9. Ben Ellison Ben Ellison says:

    No problem with the English, Pascal. But I think there’s an enormous difference between deciding to turn your own transponder off, and accepting the consequences, versus deciding to ignore whole classes of other transponders, even ones you may be on a collision course with.

  10. Anonymous says:

    Exactly, ignoring them so they don’t constantly alarm on you at every tack crossing. As AIS takes off, and it will, this is going to be very important.

  11. Ben Ellison Ben Ellison says:

    Yup, it’s also a good idea to pull the batteries out of your smoke detectors so they don’t annoy you when you make toast. It’s just too much bother to set up the alarms so they work when needed, and not otherwise.

  12. Pete says:

    Only one point that needs to me remembered here.
    It is ENTIRELY UP TO YOU to avoid a collision. It does not matter if you have the right of way or not, as the master of the vessel it depends on you and your ability to do everything to avoid it.
    Take you head out of your electronics for a bit and look around. There are a LOT of vessels that are NOT broadcasting. There are also a lot of deadheads and other objects that can cause you concern.
    Do what you can to announce your position, run the correct light or flags, use a proper radar reflector.
    But do not expect that because you are broadcasting a Class B signal that others are going to pay heed to it.
    Darwin’s law will eventually sort it all out anyway.

  13. Ben Ellison Ben Ellison says:

    The “correct flags” for collision avoidance? Pete, please do explain what those are, because I’ve never heard of them. Anyone?
    ‘Pete’ seems like a good example of what I’m talking about in this entry. He seems so determined to be pissed off about Class B electronics that he’s creating fictional users and attitudes. If there really is someone out there who thinks all vessels are broadcasting AIS or will see them on AIS, they sure didn’t read it here.
    ‘Pete’ also seem oblivious to the fact that AIS — both A and B — is coming to us from the very same folks who write the rules about ‘correct’ nav lights, day signals, etc. The very same folks who have set standards for radar reflectors (which almost no reflectors can meet). The very same good folks who are trying to save dudes like ‘Pete’ from hurting himself, and others.

  14. Sandy Daugherty says:

    Pete’s post is a meme.
    And thanks, Ben for introducing this concept to those of us who probably don’t spend a lot of time pondering the birth and spread of cultural misconceptions. A half hour on Wikipedia this morning was very interesting, and revealing.
    So, for those armchair salts who must defend the days of iron men and wooden ships from the invasion of the pocket protectors, your ideological zipper is down!

  15. S,A. Roberts says:

    Ben & Readers,
    As a pilot on the Delaware River and also an owner of a company that utilizes AIS connections (, I have been following this discussion with great interest. While it isn’t currently a problem, pilots and other large vessel operators are concerned with the potential to overload our displays with too many AIS target icons as Class B becomes more prevalent. There have been too many times to count that I wish I could ID and make contact with a yacht in a developing close quarters situation and have been unable to. I believe that Class B AIS would be a great asset in enabling communications. I, however, do not need to know what a yacht 10 miles away from me is doing. Perhaps the answer that all users could live with a some sort of range filter. The software I have used filters for Class A at any given distance. Maybe the software engineers could make a separate filter for Class B at a given distance to allow users to be able to concentrate on relevant traffic.

  16. Bob Etter says:

    Glad to hear you’re watching us (Class B)!
    Are you using the Del Pilots AIS server or do you rely on a Pilot plug?
    If/when using the Pilot Plug, how many Class B targets are you seeing at or beyond 10 miles? I ask because on Long Island Sound, I rarely see Class B beyond 6 miles or so (my antenna is about 6ft above the water line). I attribute this to the lower radiated power and probable low height of most Class B equipment.
    Obviously, if you’re using the server, you’re see everything on that network…

  17. Sandy Daugherty says:

    Most AIS B systems offer the choice to broadcast or be silent. I choose to broadcast only at night or in deteriorating weather, times when there are fewer recreational yachts about.
    I see a few AIS B targets broadcasting from their slips. I think that is excessive, such sleeping targets do clutter the screen at wider scales.

  18. Billlentz says:

    I am seeing more and more AIS targets every weekend. When I 1st installed my AIS Class B it was very rare to see many if any targets especially Class B targets. I leave mine in receive mode at the dock. It is fun watching the various ships it is also amazing that the data on many is flat out wrong. I see plenty of bad destination data on Class A ships but the data they can’t control is what is important. I have never seen a screen that was so cluttered it would be an issue. Now I am not a massive vessel where the AIS antenna could easily be quite high. I do notice propagation seems to be better in the morning. This past weekend I picked up a tug 89 miles away.

  19. S,A. Roberts says:

    Bob Etter:
    I have seen as many as 177 targets at once from as far away as Narragansett Bay to Norfolk using our server. I haven’t seen many Class B’s at all yet on the Delaware using the server or a pilot plug connection. Given the height of a ship’s antenna at around 100′, I’m sure we’ll see them out farther than six miles. It may be that target overload is self-limiting due to the shorter range of Class B installations. I’m just interested in a little feedback on the subject of filtering.

  20. Bob Etter says:

    S,A Roberts:
    Yes, the “filtering” issue is one I’m interested in also. I think that between the RF limitations (both from the TX design and physical install) of Class B and it’s inherent “politeness” in fitting transmissions into available slots, Class B “overload” will be a non-issue. I’ve made a number of transits of the Delaware, both offshore and up the Bay/River and found it an AIS target-rich region. Most recently, I was Northbound for Long Island Sound about 12 miles offshore and used the opportunity to query a number of Class A vessels in and outbound in both the North and South approach. My visibility in terms of a target on a screen on the bridge was all over the map depending on their equipment and expertise but what was consistant was my range, between 10 and 15 miles.
    In terms of “screen clutter”, a number of years ago somebody had a TCP/IP feed up (I believe it was related to N-AIS testing) that sometimes had the entire US coastline on it. One nite, I had many thousands of targets (all Class A, of course) in my AIS vessels’ panel (MacENC). Small scale views were, of course, just blobs of yellow around major ports. As I zoomed in, resolution increased and target separation increased. My opinion is that AIS target resolution (and screen clutter) will be pretty much operator driven…if you are in a target rich area, you’ll zoom in to “open up” your display, just as you would go from an approach chart to a harbor chart when closing the coast. Obviously, there will be times when the chart geography will be obscured by targets (both Class A and B) and you’ll want to be able to remove them from the display temporarily. MacENC can either remove individual targets (a visually prominent check box in the AIS panel next to the vessel’s info) or do it globally (selecting “Stationary” and/or “Underway” in an upper layer menu) and I would assume that most other software has similar functionality. I think that the important thing here is that any filtering be at the uppermost layer of the of the UI so it is always available (as opposed to an operator having to dig into a menu) and that Class A and B targets are treated equally.
    Lastly, Class B has been approved in Europe for some time now and widely adopted. I’ve not seen any indication of problems or complaints.

  21. Ben Ellison Ben Ellison says:

    Thanks, Bob! I’m glad to hear you’re being seen at 10-15 miles. Another ‘meme’ running around about Class B is that it only transmits a couple of miles. What is your set-up…antenna type, height, etc.?
    I agree that the cluttering issue is overblown. We will figure out ways to deal without totally ignoring any potentially dangerous targets. In fact, any vessel that totally ignores potentially dangerous targets, even little bitty Class B ones, is putting themselves in a bad place liability wise.
    Here’s a relevant comment I just came across at (where Class B skepticism runs strong).
    Do the Big ships filter Class B?
    by wraywest on 15-Jul 15:13
    I asked this of my friend that is the captain of one of the Exxon supertankers that go in and out of Seattle, San Fran, and Long Beach.
    His answer: I don’t know of any way to turn it off. And even if I did have a way to turn it off, that would be stupid. Any information I can get about all the radar targets out there make my life much easier. I’ll take any information I can get. My screens have plenty of room. I am starting to see pleasure boats show up on the AIS and it makes my job easier.
    My observations: The big ships don’t want to hit anyone and they don’t just plow through and hope everyone will get out of the way. Anything we can do to help them operate safely is a good thing. Giving them a way to hail us is great, if they need it.

  22. Anonymous says:

    My antenna is about 6′ above the deck which is about 4′ above the waterline, so about 10′ total above the waterline. It’s a standard Shakespeare VHF antenna fed with about 30′ of R8X. I have a Comar CSB200. The 10-15nm range is what I KNOW I’m getting as a result of responses I get from others….I’m sure it’s often far greater than that.
    What people seem to forget is that the AIS system was conceived, designed and implemented by multiple organizations that have some expertise in this area. It’s specifications and regulations didn’t come about willy-nilly but as a result of research, experience and extensive testing. I would hazard a guess that a lot of the mis-information out there is coming from the same people that will broadcast over VHF, “Breaker one-six, breaker one-six for a radio check”. AIS isn’t just another toy you plug in on your boat, it’s a seriously functional system the benefits of which we are just beginning to realize.
    Bob Etter

  23. del says:

    For what it’s worth, I have an antenna mounted on the roof of our office, which is a good 20nm inland, and we regularly pick up Class B’s from 20-30nm.
    Granted, this isn’t a “normal” configuration, but it does go to show that Class B’s CAN be received at reasonable distances.

  24. del says:

    For what it’s worth, I have an antenna mounted on the roof of our office, which is a good 20nm inland, and we regularly pick up Class B’s from 20-30nm.
    Granted, this isn’t a “normal” configuration, but it does go to show that Class B’s CAN be received at reasonable distances.
    And, Bob, as I was one of the engineers that had to sit through the endless standards meetings to define the Class B, thanks for the vote of confidence – I think its the first one I’ve had!

  25. Dan Corcoran (b393capt) says:

    I keep reading these installation posts .. just waiting for someone to say they installed it on the stern rail of the 30-40 foot boat, a total distance of 5 feet from the base of the antenna to the water and get x (or xx) miles.
    I have a strong suspicion that there is no need to mount the antenna any higher for the average user that simply wants to avoid collisions.
    I suspect a stern rail vs. a cabin top of mast keeps this a DIY project for many of us, as a stern rail installation often can have the wiring run first thru a locker, making it easy to establish a water tight connection that is easily installed, observable, and not a terrible problem if we get it wrong and it leaks. Also of course, no headliners to deal with in the cabin and establishing a suitable distance from other VHF antennas is a breeze.

  26. Both antennas for Barbara’s class B (ACR) installation are on the pilothouse top, about 11′-6″ off the water. I see ships often at great distances (of course), and I find that they see me in plenty of time (though I don’t know how far away really).
    Was really an easy install compared to lots of stuff.

  27. Kamaloha says:

    I find it hard to believe in this litigious day and age that any commercial manufacturer would include the ability to disable safety-at-sea systems in their products. They are just opening up their wallets.
    I saw Gizmo show up on my Vesper Watchmate screen last month as I sailed in the fog up to Isleboro. I could tell by the range and bearing you were in Camden, and I almost stopped in to meet and greet, but I was headed up to the SSCA Gam.
    That would be the same trip where the USCGC Eagle hailed ME by name on Ch 16. Personally I love the AIS!
    My biggest gripe is that 300 tons is way too large a threshold for implementation – I would think that something like 60 feet, where the line is drawn for larger nav lights, would be better. Clearly a boat that large has the infrastructure to support AIS. I’m sure you noticed the Penobscot Bay ferries, quiet and deadly in the fog, were NOT equipped – that is because they only weigh in at 260-some tons.
    Penny-wise, pound foolish.

  28. Agreed about the 300-ton threshold. I’d agree with 60′ — and actually I’d like to see anything over 40′ with a COI, and especially tugs (though more and more tugs are getting AIS).

  29. Roger says:

    I have posted on this issue before and asked the same question.
    The IMO mandated the carriage of AIS as follows-
    Quote “The regulation requires AIS to be fitted aboard all ships of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages and all passenger ships irrespective of size. The requirement became effective for all ships by 31 December 2004.”
    This surely includes ferries. What am I missing?

  30. Ben Ellison Ben Ellison says:

    I don’t know what you’re missing, Roger, but there surely are a lot of large domestic ferries in the U.S. which are not AIS equipped. I don’t think they’re flouting the law, but it does surprise me that more haven’t adopted the technology voluntarily.
    At any rate, the U.S. Coast Guard is working on a rule change that will mandate AIS transponders, A or B, on some 15,000 commercial vessels, lots of ferries included. If anyone knows the latest on this, I’m sure Panbots would like to know (me included).
    PS. Kamaloha, I see your AIS signal often, usually laying in Rockland Harbor. What sort of transponder and antenna are you using?

  31. Bill Lentz says:

    My antenna is a Digital cut specifically for AIS. It is mounted 13’6″ above the water. I have RG8X about 25 feet to the Navionics 300L Class B transponder I normally see other Class B vessels about 5 miles out and Class a 15 to 20 miles. During the night when we get tropo (temperature inversion) I once saw a Class A vessel at 89 miles. That same night I had Class B vessels at 25 miles. I’m still happy to report almost every trip to the boat and there are new Class B vessels. To me this is a great thing and eventually I believe it will become a standard. I only have a 40 foot vessel but I am going to install a unit in our 20 foot boat with a low antenna for when the kids take the boat out, Mom and Dad will be able to see where they are at all times. They all have NJ boater safety cards now mandatory in NJ.
    Bill Lentz

  32. Scott Garren says:

    I just installed a Comar class B transponder. Very easy install and very little more than just a receiver. I have no data to add to the debate but a suggestion. I am now sitting in the lagoon in St Martin and there must be 100 yachts on moorings and in marinas all transmitting AIS data. Quite impressive. I would love a filter though that suppressed the display of targets that were not moving! My screen — PC running Maxsea — is really cluttered! Not only that but when I am underway heading into the lagoon and aimed at a marina there are dozens of boats with very low CPAs. I am not counting on my AIS to help me avoid marinas. At least here and now I am really only worried about boats that are underway. Maybe a different CPA alarm threshold for moving targets would be safe?
    BTW: You can not depend at all on the Class A at anchor/underway status. From what I see here it is seldom right. Only the actual speed is useful

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