AIS A or B – A Disturbing Discovery


We have been slowly discovering the changes in the software on the Furuno 2117 radar, included in our recent upgrade. This is an IMO class piece of hardware, in other words, used on commercial vessels, and as such the interface must conform to certain international standards. The screen shot above is in t’he AIS display filter menu. Note the comments on class B AIS and minimum ship length.

We understand the reasoning, reducing clutter on the radar screen in waters crowded with AIS B equipped yachts. And the odds are most professional mariners would use this feature. The big question is will they change it back when offshore? We guess not. So, if you are trying to decide between AIS A or B, keep this in mind. With B it is safest to assume you will not be showing up on most ships.

Post Script: See Ben Ellison’s comments – it appears that we have misinterpreted this. We found a page in the Furuno 2117 manual which says:

3.14 Acquisition Zone

The acquisition zone functions both to alert you targets in a specific area and

acts as an automatic acquisition area when automatic target acquisition is active.

Any targets entering the zone will be automatically acquired.

When a target enters an acquisition zone, the buzzer sounds and the indication

TT NEW TARGET (or AIS NEW TARGET) appears (in red) in the Alert Box. The

symbol of the offending target is red and flashing. Further, the AIS display is

automatically turned on if it is off.

We will test this in the real world when we are next aboard. We hope Ben’s interpretation of the above is correct.

Second  Post Script: this issue is far from settled and we are awaiting response from Furuno. But as of Friday the 15th it appears you can disable AIS B targets.

Posted by Steve Dashew  (December 14, 2010)

9 Responses to “AIS A or B – A Disturbing Discovery”

  1. Matt Marsh Says:

    After all those assurances in the media that no, commercial transceivers do not have a big red “ignore class B” button, the truth comes out….
    They’re right, there is no big red button. It’s blue and yellow.

    Thanks for this, Steve. Perhaps it is wise to consider a class B system to be a receiver only. From a ship watchkeeper’s perspective, after all, “big is right” and the little guys should be staying out of his way; filtering out their signals might seem perfectly justifiable to him. If you want to be seen, you’d better look like something he cares about- enhanced radar cross-section, commercial class A AIS, etc.

  2. Chris Witzgall Says:

    Wow. That is really disturbing. I am sure it is something that the manufacturers of Class B transceivers don’t want us to know. I have been waiting for the Verper Marine transceiver to become available – I might opt for the receive only unit now and save some $$$.


  3. Todd Rickard Says:

    Interesting to have the option to define Minimum Ship Length. I assume this would filter class A transceivers if the operator deemed a certain sized vessel too small to be concerned about, or does this setting pertain to only class B transmissions?

  4. Steve Dashew Says:

    Hi Todd:
    It appears as this does work on A units as well. One work around is not to program the dimensional data on the yacht’s AIS A. We see a lot of smaller commercial vessels with just their MMSI number and name programmed.

  5. Matt Marsh Says:

    If you’re right about that, Steve- that these display filters can be applied to class A transmissions as well- then it is only a matter of time before the whole matter is dragged up in court somewhere, likely following a fatal collision. It won’t be a prudent, licence carrying captain from a reputable line on the stand, it’ll be a second-lieutenant watchkeeper with purchased certificates piloting a 50-year-old rustbucket. Exactly the sort of situation that AIS is supposed to help prevent.

    This sort of thing really bugs me, because all the international negotiations and engineering effort that went into the AIS system was intended to make a system so foolproof that the defence of “he didn’t show up on my screen” would be equivalent to telling the court “I’m an incompetent landlubber who has no business on a ship”. The system was carefully designed to self-organize its communication structure, to automatically correct for interference and overcrowding, to seamlessly scale to thousands of ships in a region, and to distill all the essential information down into a display that would be as easy to understand as a seven-year-old’s video game. Then we strip the thing down to its bare essentials and offer small craft a “class B” transmitter that costs peanuts, doesn’t hog the bandwidth and that’ll finally let ships see those hard-to-spot boats on the open sea. And then we go add a button for “oh, by the way, let’s just pretend we don’t see anything that might be inconvenient”.
    (end rant)

    Not to sound too cynical, Steve, for I really do think that AIS, especially when combined with a good radar and ARPA algorithm, can be a very helpful tool in making the seas safer as things get more and more crowded. But knowing how to use tools is far more important than having tools. And tools without the knowledge of how to use them can be very, very dangerous.

    PS – I suppose an alternate to the “leave LOA blank” would be the old “slip a decimal point”, which is certainly seen on occasion… 😉

  6. Ben Ellison Says:

    Hi Steve,

    Did you get a new manual with this software upgrade to the 2117? If so, it would be great if you dug into what that AIS Display menu actually means. I think you’ll find that the filtering is only about the display of “sleeping” targets, which in IMO language means non dangerous ones. I believe that your 2117 will continue to track targets regardless of the settings on that menu, and it will automatically switch them from “sleeping” to “active” (and displayed) if their CPA/TCPA warrant notice and possible action by the watch standing crew. Here’s a Panbo entry that quotes the pertinent IMO/IEC documents:

    I can’t find any 2117 manual online, but I’ll ask Furuno for details about this AIS Display menu today, as I’m already getting worried e-mails about this post and your screen shot. Many ships today have poor AIS target tracking facilities, but I believe it’s a myth that they can purposely ignore Class B targets. And while I realize that your suggestion is to carry a Class A transponder, many cruisers can’t afford one either in dollars or battery power. So based on a persistent myth, they get an AIS receiver instead of an affordable, low-power Class B transponder. That’s a shame, as I wrote here:

  7. Steve Dashew Says:

    Hi Ben:
    Sent you the manual page which only talks about turning the AIS B off. I hope you are right. Flying back to AZ so cannot test this in the real world.

  8. Ben Ellison Says:

    Hi Steve, I found the manual at FurunoUSA and it pretty much confirms my understanding of IMO AIS target standards. Filtered targets are still tracked and automatically displayed again if the target enters either of the radar’s ARPA zones. No disrespect meant, but I did call out this misunderstanding about the display menu on Panbo. The myth about ships ignoring Class B AIS transponders is widespread and damaging. Links:

  9. Matt Marsh Says:

    I,too, hope Ben’s interpretation of this is correct. Completely ignoring some signals should not be possible on an IMO approved unit. If the ability to suppress display of certain types of targets is present (which it apparently is here), there has got to be a mechanism by which the computer can override the operator’s display filter settings if it detects a target worthy of attention.