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AIS target functions · 365
AIS target functions
Introduction
An AIS transponder can be connected to the ECDIS, in where AIS targets are displayed based on information
received from the AIS transponder. The ECDIS can store simultaneous 1000 AIS targets in it's storage buffer.
Alarm 3501 inform about 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. Also the storage buffer contain calculation of range, bearing, CPA, TCPA etc. The CPA and TCPA
limits for dangerous targets are common inside ECDIS for ARPA and AIS targets.
From this storage buffer ECDIS can display AIS targets which are within user defined range. On ECDIS the
maximum count of simultaneously displayed AIS targets are limited to 200 targets. Alarm 3500 indicates that there
are more than user selected amount of AIS target within user selected range.
The frequency for update information of AIS transponder depends on speed and course change of tracked AIS target.
The current reporting rate of each AIS target is available from INFO/HELP request. Below is a table which indicate
IMO standardised reporting rates for AIS transponder. Based on table below, ECDIS defines which AIS targets are
in tracking, lost or deleted.
Type of Ship IMO nominal
reporting
interval
Lost target
indication
(reporting
interval >)
Automatic
deletion of
target
(reporting
interval >)
Ship at anchor or moored and not moving faster than 3 knots 3 min 15 min 30 min
Ship at anchor or moored and moving faster than 3 knots 10 s 50 s 1 min 40 s
Ship with a speed of between 0 - 14 knots 10 s 50 s 1 min 40 s
Ship with a speed of between 0 - 14 knots and changing course 3 1/3 s 17 s 33 s
Ship with a speed of between 14 - 23 knots 6 s 30 s 1 min
Ship with a speed of between 14 - 23 knots and changing course 2 s 10 s 20 s
Ship with a speed of greater than 23 knots 2 s 10 s 20 s
Ship with a speed of greater than 23 and changing course 2 s 10 s 20 s
Onboard AIS transponder see all vessels fitted with AIS transponder. There can be several hundreds or several
thousands of AIS targets. Only few of all AIS targets are significant for you. The ECDIS includes a concept called
"active and sleeping AIS targets". Initially any new AIS target received by the onboard AIS transponder is not-
active (="sleeping"). Such non-active targets are visualised by a small a triangle. User can pick any AIS target and
change it from non-active to active. Active AIS targets are visualised by big triangle, speed vector, headline, rot
indicator, etc.. Also user can pick active AIS targets and change them as non-active.
AIS target functions of the ECDIS include also "Alarm 3502: Dangerous AIS target" and "Alarm 3503: Lost AIS
target". Only active AIS targets create alarms. Also user can enable or disable AIS target alarms in general. The
concept called "active and sleeping AIS targets" is very effective to concentrate the focus only to AIS targets which
need supervision. The ECDIS further ease the task of the user by changing non-active targets automatically as active
targets, if they meet the dangerous target limits set by CPA and TCA.