AIS position stuck in wrong place


1 comment

  • Official comment
    Iliana Androulidaki

    Hello Ross,

    Thank you for reaching out to us.

    From what I can see, this is your vessel:
    and her latest position appears to have received on when you moored in Portsmouth, and I assume that you turned off your transponder.

    As you may know, MarineTraffic relies on the AIS Protocol in order to receive vessel positions. These positions are VHF free, non-encrypted signals transmitted by the vessels' AIS transponders, which can be interrupted by a multitude of conditions.
    As a result, the lack of Updated Positions of a vessel can be a result of a number of factors.
    Among other factors, signal strength, functional transponder, local (vessel area) and surrounding (nearby stations) weather conditions, temperatures, traffic and the satellite constellation frequency are some of the most important ones.
    The distance from the receiver, as well as the receiver altitude, may also affect the reception of signals

    You can learn more about them here:

    Moreover, for vessels equipped with Class B transponder, which is includes smaller sailing and pleasure craft vessels, I would like to inform you that both terrestrial and Satellite-AIS tracking may be less effective if the subject vessel is equipped with a Class B AIS transponder. Such units are smaller, simpler and lower cost compared to Class A transponders but their signal is weaker making it harder for stations and satellites to pick-up AIS messages coming from them.
    Note that the signal strength of the transponder also depends on the vessel's engine power, and thus most Class B transponders usually have a signal range between 5 and 20 NM.

    For all the above reasons, positions received within the past 24 hours are considered updated positions, and more importantly, it is expected that positions for Class B vessels will be more sporadic and on occasion not appear at all, exactly because the transponder's signal cannot reach our stations and/or satellite constellation.

    I hope this helps clarify things, but please feel free to reach out for anything else.
    I will be glad to assist.

    Kind regards,

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