Class B AIS, ruminations

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.

7 Responses

  1. Russ says:

    All good points. No question that the second generation will be less expensive that the first and that volume will drive cost down. And lower cost usually means lower prices and broader adoption.
    With regard to who’s watching, what do we (or really you!) already know about the Class A equipment currently installed?
    How will Class B be displayed on the existing Class A equipment?
    Is there any ability to filter the targets?

  2. Ben Ellison Ben Ellison says:

    Well, let me be clear that I do not know every technical detail of AIS, or anything else! But my understanding is that current Class A gear will see Class B dynamic data but may need a software upgrade to see a boat’s name, etc. The AIS displays on ships apparently vary hugely, from overlays on gigando ECDIS and dedicated radars to little grayscale LCDs stuck in the corner. And I believe that the ability to filter out Class B targets is permitted in the regulations, which also mandate that local authorities be able to shut down all B transmissions.

  3. Russ says:

    “And I believe that … mandate that local authorities be able to shut down all B transmissions.”
    Well that’s interesting. How would they do that? Can they send out some sort of command that shuts down the Class B transponder? Does the Class B transponder need some sort of “OK to send” signal? That sounds wild!
    I reviewed the Furuno FA-150 manual (Class A $4,000). It’s plotter display and target list do not differentiate between Class A and B, but do indicate an AtoN, SAR or BS (base station). Subequent data display pages do differentiate between A and B. I don’t see any way to filter the targets, other than it creates a separate list of “danger” targets.
    It does indicate that the AIS uses two dedicated VHF channels and “is capable of being automatically switched to designated alternate channels by means of a message from a shore facility. Perhaps this is how a Class B can be shut down.

  4. Ben Ellison Ben Ellison says:

    Getting down and dirty now, Russ! Apparently the local control capability was built into the System from early on, though still little used. Back then Class B was conceptualized but not defined, which I think explains what you see and don’t see in that Furuno manual. When the B spec was finally hammered out, it included local contol, aka frequency agility, and filtering…I think. It would be great if someone more confident about these details stepped in here, either directly or by emailing me (see contacts in right column). In the meantime, here’s some relevant dope from Oct., ’05:
    https://panbo.com/yae/archives/001145.html

  5. b393capt says:

    Ben that all sounds reasonable.
    One more thing that will eventually be in favor of having class B transiever, is when they are popular, we might want to consider that the careless boaters we fear the most, will be considering those radar returns without an associated AIS symbol … noise.

  6. Dan Gingras says:

    Ben,
    A google search turns up this:
    http://www.sailing.org/default.asp?ID=j/fFnopv&MenuID=t67mGMnon~824QM6/%60xAM4Y1TU0d6YZUhv~JMBMq/RNTdbdlYpYP3PWct8Ulz4
    Check out the paragraph titled OVERLOAD. It indicates that a shore station can turn off the class b transponders for a “short period”
    Interesting
    Dan

  7. del says:

    A “competant authority” may use special msg to shut Class B’s up in a specified area for a specified time (up to 15 minutes from memory). This was intended as an “only if everything else fails” feature and would only be used in very dire circumstances by the shore station / coastguard to ensure that Class A can be heard in the unlikely event that too many Class B’s could be overloading the channels. I emphasise that this is a feature that is not expected to see widespread or frequent use, it is there soley to ensure the ultimate integrity of the Class A and should NOT be seen as a reason to denigrate the Class B operations.

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