21-1
21. AIS Target Functions
21.1 Introduction
An AIS transponder can be connected to the ECDIS to display AIS targets received from the AIS transponder. The
ECDIS can store up to 1,500 AIS targets in its storage buffer. When this buffer becomes full of AIS targets, the
Alarm 3501 is generated to alert you to full storage buffer. The storage buffer contains automatic dead reckoning for
all AIS targets, which is based on reported Speed Over Ground (SOG), Course Over Ground (COG), Rate Of Turn
(ROT) and heading. The storage buffer also contains calculation of range, bearing, CPA, TCPA, etc. The CPA and
TCPA limits set for dangerous targets are common for ARPA and AIS targets.
ECDIS can display AIS targets which are within the operator-defined range. The maximum number of targets which
can be displayed is 200 and the operator may choose the number of targets to display. Alarm 3500 is generated
when there are more than the operator-specified amount of AIS targets within the operator-chosen range.
The frequency for update of AIS transponder-sent data depends on speed and course of tracked AIS target. The
current reporting rate of each AIS target is available by using the Help/Info feature. The table below shows the IMO
standardized reporting rates for the AIS transponder. Based on the table below, the ECDIS defines which AIS
targets are in tracking, lost or deleted.
Type of Ship IMO nominal
reporting
interval
Lost target
indication
(reporting
interval >)
Automatic
dead
reckoning of
target
(reporting
interval >)
Ship at anchor or moored and not moving faster than 3 knots 3 min 18 min 30 min
Ship at anchor or moored and moving faster than 3 knots 10 s 60 s 1 min 40 s
Ship with a speed of between 0 - 14 knots 10 s 60 s 1 min 40 s
Ship with a speed of between 0 - 14 knots and changing course 3 1/3 s 60 s 33 s
Ship with a speed of between 14 - 23 knots 6 s 36 s 1 min
Ship with a speed of between 14 - 23 knots and changing
course
2 s 36 s 20 s
Ship with a speed of greater than 23 knots 2 s 12 s 20 s
Ship with a speed of greater than 23 and changing course 2 s 12 s 20 s
An AIS transponder "sees" all ships fitted with an AIS transponder. There can be several hundreds or several
thousands of AIS targets, and of those only a few will be significant for your ship. To remove unnecessary AIS
targets from the ECDIS display, the feature "active and sleeping AIS targets" is available. Initially any new AIS
target received by an AIS transponder is not-active (="sleeping"). Such non-active targets are shown with a small
triangle. User can pick any AIS target and change it from non-active to active. Active AIS targets are shown with a
large triangle with speed vector, headline, rot indicator, etc. Further, the operator can pick active AIS targets and
change their status to non-active.
ECDIS generates AIS-related alarms and these are "Alarm 3502: Dangerous AIS target" and "Alarm 3503: Lost AIS
target". Only active AIS targets generate alarms. The operator can enable or disable AIS target alarms as desired.
The feature "active and sleeping AIS targets" is very effective for focusing on only those AIS targets which need
supervision. The ECDIS further eases the task of the operator by automatically changing non-active targets to active
targets, if they meet the dangerous target limits set by CPA and TCPA.
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