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5.3.10 Conditions for Deciding AIS Target to be Lost
About a lost target
When the data of an AIS 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 receive data and the target status.
[SOLAS ship] (Class A)
Target Status Time until data deletion
Vessel below 3 knots and it is now at anchor or on the berth
18 min
Vessel of 3 knots or more and it is now at anchor or on the berth
60 sec
Vessel of 0 to 14 knots
60 sec
Vessel of 0 to 14 knots and it is now changing the course
60 sec
Vessel of 14 to 23 knots
36 sec
Vessel of 14 to 23 knots and it is now changing the course
36 sec
Vessel over 23 knots.
12 sec
Vessel over 23 knots and it is now changing the course
12 sec
[Non-SOLAS ship] (Class B)
Target Status Time until data deletion
Vessel below 2 knots
18 min
Vessel of 2 to 14 knots
180 sec
Vessel of 14 to 23 knots
90 sec
Vessel over 23 knots
30 sec
Reference:
• 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 a
maximum of one minute. If the system cannot receive any data within one minute or the ALARM ACK
switch is pressed, the symbol is cleared.
• When a safe target ship is lost, the system does not issue a lost alarm, display a lost symbol, or calculate the
current position.
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