Section 6 Target Tracking and AIS 6-38
6.6.7 Conditions for deciding AIS target to be lost
About an AIS target lost
When the data of a target cannot be received for a specified time, the target is decided to be lost and
the target data is deleted. As shown in the table below, the time until target data is deleted varies
depending on the class of received data and the target status.
• Since the lost time and that of the AIS indicator are different, this equipment may display lost
information earlier than the AIS display depending on the target status (speed, navigation
status, etc.).
• The target of lost target is continuously displayed until Lost Warning is approved.
Since negligence of approval operation may hinder display of a new AIS target, perform
approval operation as soon as possible.
• When a dangerous target ship is lost, a lost alarm is issued and the symbol changes to a lost
symbol. The system calculates the current position from the last-received data and continues
displaying the symbol for eternity.
• When the [AIS] button in the target ship information window is turned off, the symbol is
Conditions for Deciding Target to be Lost
Target status
Time until data is lost
SOLAS ship
(Class A)
Non-SOLAS ship
(Class B)
CS (Carrier
Sense)
SO (Self
Organising)
Vessel below 3 kn (Class A) or 2 kn (Class B) and
it is now at anchor or on the berth
18 min 18 min
Vessel of 3 kn or more and it is now at anchor or
on the berth
60 sec -
Vessel of 0 to 14 kn (Class B: 2 to 14 knots) 60 sec 180 sec
Vessel of 0 to 14 kn and it is now changing the
course
60 sec 180 sec
Vessel of 14 to 23 knots 36 sec 180 sec 90 sec
Vessel of 14 to 23 kn and it is now changing the
course
36 sec 180 sec 90 sec
Vessel of 23 kn or more 30 sec 180 sec 30 sec
Vessel of 23 kn or more and it is now changing the
course
30 sec 180 sec 30 sec
AtoN (Aids to navigation) 15 min 15 min
SART 6 min 6 min
AIS SAR aircraft 60 sec 60 sec
AIS coastal base station 60 sec 60 sec
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