VHF Radio Transmissions’ Impact On AIS Reception


USCG published a safety alert in which highlights that a very high frequency (VHF) maritime radio transmission on one’s own vessel, or even transmissions by a nearby vessel a football field’s length away (about 136 meters or 445 feet), may block AIS reception for the duration the radio is keyed.

An analysis of the relevant standards has shown that this may impact all classes of AIS equipment regardless of how the antennas for the two systems are installed.

Revised guidelines

As stated in IMO Resolution A.1106(29) Revised Guidelines for the Onboard Operational Use of Shipborne Automatic Identification Systems (AIS), users should not rely on AIS as the sole information system for collision avoidance or navigation decision-making, but should make use of all safety relevant information.

Delayed updates to AIS positions and Aid to Navigation reports caused by keyed VHF radio transmitters, as well as possible loss of certain safety-related messages, are examples of why the AIS should not be solely relied upon for collision avoidance. Navigators are further reminded of Navigation Rule 7 – Risk of Collision, which states that “every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists” and that “assumptions shall not be made on the basis of scanty information”, such as AIS.

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Source : Safety4sea


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