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5-1
5. AIS Operation
An AIS transponder can be connected to the Chart Radar to display AIS targets received from the AIS transponder.
The Chart Radar can store up to 1,500 AIS targets in its storage buffer. When this buffer becomes full of AIS
targets, the Alert 639 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 TT and AIS targets.
The chart radar can display AIS targets that are within the operator-defined range (max. range is 48 nm). The
maximum number of targets that can be displayed is 240 and the operator may choose the number of targets to
display. Alert 637 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 table
below shows the IMO standardized reporting rates for the AIS transponder. Based on the table below, the chart radar
defines which AIS targets are in tracking, lost or deleted. When you acknowledge a lost target alert, AIS symbol will
be removed from the display. If lost target is not acknowledged, automatic removal of AIS symbol is done as shown
table below.
Type of Ship IMO nominal
reporting
interval
Lost target
indication
(reporting
interval >)
Pre-set rate
for automatic
removal of
lost target
Class A: speed between 0-14 kn 10 s 50 s 430 s
Class A: speed between 14-23 kn 6 s 30 s 430 s
Class A: speed greater than 23 kn 2 s 10 s 430 s
Class A: anchored, moored, not under control or grounded,
speed between 0-3 kn
3 min 10 min 36 min
Class A: anchored, moored, not under control or grounded,
speed greater than 3 kn
10 s 50 s 36 min
Class B: CS speed between 0-2 kn 3 min 10 min 36 min
Class B: CS speed greater than 2 kn 30 s 150 s 430 s
Class B: SOTDMA speed between 0-2 kn 3 min 10 min 36 min
Class B: SOTDMA speed between 2-14 kn 30 s 150 s 430 s
Class B: SOTDMA speed between 14-23 kn 15 s 75 s 430 s
Class B: SOTDMA speed greater than 23 kn 5 s 25 s 430 s
Class A and Class B: no speed available N/A 10 min 36 min
ATON 3 min 10 min 30 min
SAR 10 s 50 s 430 s
Base station 10 s 50 s 430 s
SART N/A 10 min 30 min
An AIS transponder "sees" all ships fitted with an AIS transponder belonging to either
• Class A AIS
• Class B AIS
Additionally the AIS transponder receives messages from ships and these non-ships:
• AIS Base station
• AIS on airborne SAR craft
• AIS on ATON (AIS aid to navigation)
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 Chart Radar 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