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  1. #1
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    May 2001
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    Default VHF / Chartplotter integration for DSC (MOB)

    I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.

    When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

    I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism

  2. #2
    Join Date
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    Default Re: VHF / Chartplotter integration for DSC (MOB)

    I believe that most plotters should display DSC messages. However, I understand that not all radios will sound an alarm in response to the individual distress relay call from MOB devices, it depends on the radio. Newer radios should work OK.

    Similarly, I understand that not all plotters can properly handle the AIS alert from MOB devices, and may not display an alarm message. Again, newer plotters ought to display it properly.
    Last edited by pvb; 16-08-19 at 11:51.

  3. #3
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    May 2001
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    Default Re: VHF / Chartplotter integration for DSC (MOB)

    These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds

  4. #4
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    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Quote Originally Posted by bedouin View Post
    These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds
    Most AIS MOB devices can send a test message.

  5. #5
    Join Date
    Aug 2011
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    On the Celtic Fringe
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    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Quote Originally Posted by bedouin View Post
    I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.

    When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

    I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism
    NO. I can't see any NMEA message sentences for converting a DSC distress CH70 message to NMEA so that it can be displayed on a chartplotter.
    Last edited by Sandy; 16-08-19 at 12:11.
    Cynical Scottish very nearly retired engineer who sails a Gib'Sea 96.

  6. #6
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    May 2001
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    24,912

    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Quote Originally Posted by pvb View Post
    Most AIS MOB devices can send a test message.
    I am thinking more about the DSC side - so does a DSC HH VHF do almost as good a job as an AIS MOB.

  7. #7
    Join Date
    Jul 2009
    Location
    Winter in Falmouth, summer on board Rampage.
    Posts
    5,192

    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Quote Originally Posted by bedouin View Post
    I am thinking more about the DSC side - so does a DSC HH VHF do almost as good a job as an AIS MOB.
    No, it does a different job. An AIS MOB transmits repeated messages with updated position fixes via the AIS system until it’s turned off. It is also automatic provided it’s been set up properly on your lifejacket.
    A HH DSC VHF requires you to press a button to send a single DSC alert: not much use if you’re unable to turn the HH VHF on and press the button.

  8. #8
    Join Date
    May 2001
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    24,912

    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Quote Originally Posted by duncan99210 View Post
    No, it does a different job. An AIS MOB transmits repeated messages with updated position fixes via the AIS system until it’s turned off. It is also automatic provided it’s been set up properly on your lifejacket.
    A HH DSC VHF requires you to press a button to send a single DSC alert: not much use if you’re unable to turn the HH VHF on and press the button.
    Yes - I understand the difference.

    For a piece of electronics to carry in case of MOB there is really the choice between PLB, AIS, VHF and you can't really carry all 3. When single handing the PLB is certainly the best option but when sailing quth crew it is different - then there is benefit in the MOB being able to transmit directly to the boat via VHF (either DSC or AIS).

  9. #9
    Join Date
    Apr 2006
    Location
    Portsmouth, UK
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    2,948

    Default Re: VHF / Chartplotter integration for DSC (MOB)

    The Ocean Signal Mob1 personal beacon actually sends both a DSC distress alert and an AIS man overboard alert. It should therefore show as AIS position alert on the chart plotter and as a DSC alarm sound on the radio.

    As to your first question, you've not mentioned which plotter nor radio you have but our B&G Zeus plotters happily plot the location of the messages they receive from the Standard Horizon VHF radio via an NMEA0183 connection.

    To test the DSC sentences before we got the Mob1s, I did some VHF position requests from the fixed VHF to the Standard Horizon handhelds. The handheld positions then appeared on the plotter in the correct positions.

  10. #10
    Join Date
    Nov 2013
    Posts
    1,555

    Default Re: VHF / Chartplotter integration for DSC (MOB)

    Wow. For a thread on here it might have set a new record. It took 7 or 8 posts to get the right answer and the rest is mostly non-sense!

    Quote Originally Posted by bedouin View Post
    I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.
    So start by telling us WHAT Plotter, and WHAT VHF!


    Quote Originally Posted by bedouin View Post
    When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

    I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism
    Tell us the models.

    Quote Originally Posted by pvb View Post
    I believe that most plotters should display DSC messages. However, I understand that not all radios will sound an alarm in response to the individual distress relay call from MOB devices, it depends on the radio. Newer radios should work OK.
    A DSC distress alert from a HH or a fixed unit will do the necessary on a DSC radio. So my understanding of the Ocean Signal MOB1 - is it will do that using DSC as a CH70 DSC alert with distress type MOB. Then continue to send AIS messages with position updates.

    Quote Originally Posted by pvb View Post
    Similarly, I understand that not all plotters can properly handle the AIS alert from MOB devices, and may not display an alarm message. Again, newer plotters ought to display it properly.
    Almost all will display something - they may not flash or scream or show a lifering. But provided the DSC has screached and so you know you need to go back and pick someone up, all you need to do is work out which target to go and get...

    Quote Originally Posted by bedouin View Post
    These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds
    True. But you can using a position request to see if that position will appear on the plotter.
    You can wait for a genuine DSC alert from another vessel and see it plotted (easier on the South Coast where someone will press it because they are running late for tea with Lord Montifly because the wind has dropped.
    If you know the sentence sent by the radio, you can simulate it using a PC feeding the NMEA to see how the plotter handles it.

    Quote Originally Posted by Sandy View Post
    NO. I can't see any NMEA message sentences for converting a DSC distress CH70 message to NMEA so that it can be displayed on a chartplotter.
    Well since this has been a thing for years to send the DSC position to a plotter - the sentence exists. Its a DSC sentence or a DSE sentence.
    DSC has:
    flag for –distress alert call.
    the MMSI of the sender.
    distress type & nature
    position & time

    DSE - carries more refined position data


    If you program your handheld device with the MMSI which your radio / plotter knows as your boat - it is possible there will be filtering taking place to not show it.

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