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Operations
AIS System
AIS is an Automatic Identification System. It has been introduced to improve the safety of navigation
by assisting in the efficient operation of ship to ship, ship reporting and VTS applications. The system
should enable operators to obtain information from the ship automatically, requiring a minimum of
involvement of ship’s personnel, and should have a high level of availability.
Connecting to the chart plotter an AIS receiver, vessels with AIS transponder within VHF range are
displayed on screen giving he skipper or navigator a visual interpretation of the data of nearby vessels.
This improves safety, and specifically for collision avoidance reasons.
1.AIS system definitions
CPA
Closest Point of Approach is the closest distance that will be achieved between
your vessel and the tracked target, based on your vessel’s speed and direction
and the target’s speed and direction.
CPA Alarm
Occurs if CPA is less or equal to CPA Radius. This test is done for active targets
only.
CPA Limit
This is the distance from your vessel that a target may reach before a target is
deemed a threat.
TCPA
Time to Closest Point of Approach is the time remaining until the CPA will occur.
TCPA Alarm
Occurs if TCPA is less or equal to TCPA Radius. This test is done for active targets
only and if CPA value is less or equal to CPA Radius.
TCPA Limit
This is the time remaining before the CPA is reached.
Name
Name of ship, 20 characters.
MMSI
Maritime Mobile Service Identity.
MMSI number
A unique 9 digit number that is assigned to DSC radio station. It primarily registers
the boat information in the U.S. Coast Guard’s national distress database for use
in emergency situations.
Target
It is a vessel equipped with AIS. Information about the targets is being received by
AIS Receiver and displayed on the screen.
Active Target
Target located within the Activation Range. Active target is represented by oriented
triangle with COG and Heading vectors. Rate of turn may also be displayed.
Dangerous
Target
Target detected by CPA or TCPA Alarm. Dangerous target is Active Target by
definition. For better visibility Dangerous Target symbol is charged from basic color
to red color.
Sleeping
Target
Target located outside the Activation Range. Sleeping target is represented by a
small oriented triangle.
