The poster depicts a scenario, according to which a ship is in an area of high traffic density. The master has just arrived on the bridge and is asking the officer of the watch (OOW) what the container ship is doing. The flustered junior OOW has not actually seen the ship, even though it is clearly visible. The container ship is not transmitting AIS and therefore is not being displayed on the ECDIS.
The radar, which is clearly not being monitored, shows the target quite clearly. If the ECDIS had a radar overlay installed, the ship would show up on the screen, but without any AIS data.
AIS relies on a ship to transmit the appropriate signal and therefore the ship keeping look-out has no control over the accuracy of the information received. For this reason,the COLREGs do not specifically recognise AIS as an aid to collision avoidance. Information obtained from AIS does not become more reliable or accurate merely because it is displayed on an ECDIS screen. Rule 7(c) states that assumptions shall not be made on the basis of‘scanty information’.
The Club notes that AIS, whether displayed on an Look-out and Automatic Identification Systems (AIS) ECDIS screen or not, may be one of the means that help shippers to make a full appraisal of the situation, but should not be the only means. The ARPA radar is more reliable than the AIS feed, which may be incorrect, as the ARPA will provide course and speed and closest point of approach of the target ship, based on a series of ranges and bearings.
The Club’s loss prevention team highlights that over-reliance on the data presented on the ECDIS screen is often the cause of many navigational errors and resulting incidents, as a simple visual observation is often forgotten.
Source: Britannia P&I Club