Class B, name game #2

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now excited to have Ben Stein as very able publisher, webmaster, and editing colleague. Panbo is going to the next level in 2019 and beyond.

17 Responses

  1. Sandy says:

    I’m curious about the “safety related message”. that is the alternative to a silent mode switch.
    What is it, and what advantages does it offer?

  2. Ben Ellison Ben Ellison says:

    Sandy, My impression is that the SRM capability of Class B is a subset of the ship-to-ship or ship-to-all messaging built into Class A. To my knowledge, the latter is not being used very much.
    So far, I’ve only seen a couple of plotters or charting programs that know how to notify a user of any AIS text message and display it on screen. In fact, last weekend I accidentally send an SRM with one of the Class B transponders I’m testing. It was received fine by the other B that was running, but I had to dig down in its included software to see it. I think that SRM is a possibly valuable feature built into AIS, but we have a ways to go before it is really usable.

  3. richardstephens says:

    I wonder, do the class B transponders have an NMEA input for compass heading? There is provision for heading in the message specs…

  4. Ben Ellison Ben Ellison says:

    I think the Furuno FA50 does support heading input, but I have not seen any mention of this in other Class B transponders. Do you think it’s important, Richard?

  5. richardstephens says:

    I guess heading is not that important. I was just thinking about improving Memory-Map’s CPA alarm feature for class B, and the heading is there as a potential piece of data. But as there is no input on the SR-based transponders it is probably not worth using it.
    Collision detection with class B is actually quite a difficult technical problem. Big ships turn and change speed slowly relative to the position report frequency of a class A AIS. Smaller vessels turn and change speed much faster, while the class B position updates are less frequent. In mathematical terms, the signal is sampled at less than the Nyquist rate, which means it is theoretically impossible to predict the future. The only thing I can do is assume that Gizmo will maneuver like a super-tanker.
    It would be interesting to know whether the transponder does any filtering of the vessel’s position, course and speed, or whether it just outputs the latest values from the GPS.
    The bottom line, for both developers and users, is that we are going to have to treat CPA predictions for smaller vessels quite differently from those for big ships.

  6. Nick Heyes says:

    We can multiplex a heading input into our AIT250 Class B unit. There is an NMEA in as well as a NMEA output. Most users get great results, however, with just the on board calculations of course over ground (COG) from the in built GPS module

  7. Ben Ellison Ben Ellison says:

    Thanks, Nick, I missed that. And I’d guess that if your AIT250 can mix in 0183 heading, maybe all the SRT Class B transponders can.
    Personally I can see real value in adding heading for better plotting my own vessel, i.e. being able to compare heading and COG and hence see current set and/or leeway. That is, if my plotter or charting program wasn’t getting such information via another port.
    But I don’t think heading info in my AIS broadcasts will make much difference to other vessels and their ability to avoid close encounters with me. And bad heading info can make AIS targets look odd. On the other hand, accurate heading info makes a stopped target plot correctly.

  8. Dan (b393capt) says:

    Jim, an owner of a sailboat like mine, is complaining about the alarms on his receiver only AIS unit from Raymarine. It essentially is acting like a proximity alarm, e.g. if your course is going to bring you within a 600 foot circle around any AIS vessel it alarms. It’s annoying now, and he is concerned it gets worse when AIS-B begins to be used.
    He is also complaining that AIS-A targets are already cluttering his chartplotter.
    Is this just a Raymarine issue, or is that how alarms work ?

  9. Ben Ellison Ben Ellison says:

    The only unwanted, uncontrollable AIS alarms I’ve heard of involve Raymarine MFDs, but I thought they fixed the issue with the last big update.
    Where is your friend experiencing AIS clutter and on what display?

  10. Tim Flanagan says:

    I was pretty annoyed by the constant “Dangerous Target” alarms my Raymarine C-80 kept generating, but it turns out the radius of the “danger” circle is configurable, and the alarm can be turned off completely, which is what I’ve done. Dangerous targets still have a flashing outline applied to them on the display, which is great, but I no longer get an audible alarm that requires a manual acknowledgement. Much, much better.

  11. Lee Simpson says:

    Have you heard anything yet about the Coast Guard having the ability to put a “ghost” AIS target in the system to identify vessels in distress. this would help nearby vessels to locate vessels in distress.
    Everytime they broadcast LL I don’t seem to have a pencil handy.

  12. John says:

    It’s interesting to note that, unless my information is incorrect, coastal ferries are not required to carry AIS. Our home port is in Long Island Sound & we travel up the coast to Maine late summer every year. I installed a Furuno FA150 Class A unit early this year with the main reason being the ferries seem to be getting faster & stealthier every year. There was a collision in July of this year between a ferry, Point Judith to Block Island bound, & a USCG tug, Newport to New London bound, in dense–200yd visibility–fog in Block Island Sound. Reportedly the fog had dropped rather sudden & the CG tug slowed to 9kts while the ferry had maintained its 14.5kt normal cruise. Ferry rammed the tug amidships. (See Professional Mariner Oct/Nov 2008.)

  13. Ben Ellison Ben Ellison says:

    You’re right, John. The Maine State ferries don’t carry AIS either, and they often run in fog. I think there are a number of commercial vessels like these that should have adopted Class A AIS voluntarily. But it’s all going to change when the USCG issues its next round of compulsory AIS carriage. It will take about two years, they estimate, for the rule to be enacted and deadlines met, but 14-17,000 more U.S. commercial vessels will be carrying AIS, either A or B models (apparently the rules will vary).
    Lee, I hadn’t heard that idea about marking a distress site, but it makes sense and I believe that it could be fairly easily done, at least by AIS Base Stations.

  14. richardstephens says:

    I do think an effective CPA alarm is very important. For example, it might have prevented the recent collision between the Vendee Globe boat “Hugo Boss” and a fishing boat off Les Sables d’Olonne. A lot of accidents happen when people are simply not paying attention.

  15. Eric says:

    Many have considered the concept of creating Virtual Aids to Navigation(VATONs )using AIS for a while now.
    For example, a USCG AIS Monitoring Station could easily generate a virtual bouy to mark a temporary danger zone or several virtual points to mark oil spill.
    Theoretically, virtual bouys could be used everywhere and everyone who has a low cost AIS Receiver could use them for enhanced navigation.
    I believe a big consideration is the cost saving aspects of VATONs….

  16. Dan (b393capt) says:

    Ben, Jim sails out of Mystic, Connecticut.
    He replied that he has not updated his Raymarine chartplotter. He has has been negative on our Beneteau group about AIS, hopefully the new release will make him a believer.

  17. rick says:

    I just finished installing a Nauticast-B AIS transponder. The display device is a Northstar 557 GPS. On testing, I discovered that the AIS data includes my own ship data as well as the received data. The Northstar GPS apparently was never tested with a transponder because it persists in sounding the proximity alarm because I’m too close to myself. This makes the alarm function completely useless. So far, Northstar won’t even answer my emails on the subject.

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