3. TARGET TRACKING (TT)
3-21
3.13 TT
Collision
Alarm
(CPA,
TCPA)
The TT continuously monitors the predicted
range at the Closest Point of Approach
(CPA) and predicted time to CPA (TCPA) of
each TT. When the predicted CPA of any
TT becomes smaller than a preset CPA
range and its predicted TCPA less than a
preset TCPA limit, the audio alarm sounds
and TT COLLISION appears (in red) in the
Alert Box. In addition, the symbol of the
offending TT is red and flashes together with its vector.
This feature, when used correctly, helps prevent the risk of collision by alerting
you to threatening targets. It is important that GAIN, A/C SEA, A/C RAIN and
other radar controls are properly adjusted.
CPA and TCPA ranges must be set up properly taking into consideration the size,
tonnage, speed, turning performance and other characteristics of own ship.
The reference point for CPA and TCPA calculation may be selected from
antenna position or conning position. For further details, see section 1.50.
3.13.1
Setting the CPA and TCPA ranges
To set the CPA and TCPA ranges, do the following:
1. Left-click CPA LIMIT box to show the CPA and TCPA boxes.
CPA LIMIT 0.5NM 10MIN
TCPA Box
CPA LIMIT Box
CPA Box
CPA LIMIT, CPA and TCPA boxes
2. Select the CPA Box.
3. Push the left button or scrollwheel to select CPA value.
Left button
0.5, 1, 1.5, 2, 3, 4, 5, 6(nm)
Scrollwheel
0.1-20(nm), 0-10 nm in 0.1 nm increments, 10 nm
increments thereafter
4. Select the TCPA box.
5. Push the left button or scrollwheel to select TCPA value.
Left button
1, 2, 3, 4, 5, 6, 12, 15(minutes)
Scrollwheel
1-60 minutes, 1-minute increment
CAUTION
CPA/TCPA Alarm
The CPA and TCPA alarm feature should
never be relied upon as the sole means for
detecting the risk of collision.The navigator
is not relieved of the responsibility to keep
visual lookout for avoiding collisions,
whether or not the radar or other plotting
aid is in use.
