Ais; 4.8.1 Ais System Definitions - Interphase Chart Master Chart Master 11 CVS+ User Manual

4.8

AIS

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. AIS transponders
installed on IMO vessels use VHF frequencies to:
Transmit details of their own vessel
Receive details from other vessels or navigation aids within VHF range.
Information being transmitted from vessels over 300 tons that, due to recent
worldwide legislation, are required to fit Class "A" AIS transponders.
Connecting to the chart plotter an AIS receiver (please contact your local dealer),
vessels with AIS transponder within VHF range are displayed on screen giving the
skipper or navigator a visual interpretation of the data of nearby vessels. This
improves safety, and specifically for collision avoidance reasons.

4.8.1 AIS System Definitions

Target
It is a vessel equipped with AIS. Information about the Targets is being
received by AIS Receiver and displayed on the screen.
CPA
Closest Point of Approach is the closest distance that will be achieved be-
tween your vessel and the tracked Target, based on your vessel's speed
and direction and the Target's speed and direction.
CPA Limit
This is the distance from your vessel that a Target may reach before a
Target is deemed a threat.
CPA Alarm
Occurs if CPA is less or equal to CPA Limit. This test is done for active
Targets only.
TCPA
Time to closest Point of Approach is the time remaining until the CPA will occur.
TCPA Limit
This is the time remaining before the CPA is reached.
TCPA Alarm
Occurs if TCPA is less or equal to TCPA Limit. This test is done for active
Targets only and if CPA value is less or equal to CPA Limit.
Radio Call Sign
International call sign assigned to vessel, often used on voice radio.
Name
Name of ship, 20 characters.
MMSI
Maritime Mobile Service Identity.
MMSI number
A unique 9 digit number that is assigned to a DSC radio station. It prima-
rily registers the boat information in the U.S. Coast Guard's national dis-
tress database for use in emergency situations.
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 flashing.
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