3. TARGET TRACKING (TT)
3-21
3.15 Collision Alarm (CPA, TCPA)
This radar calculates CPA and TCPA by using own ship and relative target positions.
The TT continuously monitors the pre-
dicted range at the Closest Point of Ap-
proach (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 "CPA/TCPA" appears (in red,
flashing) 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 con-
trols are properly adjusted.
CPA and TCPA ranges must be set up properly taking into consideration the size, ton-
nage, speed, turning performance and other characteristics of own ship.
The reference point for CPA and TCPA calculation can be selected from antenna po-
sition or conning position. For further details, see section 1.50.
3.15.1 How to set the CPA and TCPA ranges
CPA and TCPA ranges can be adjusted from the ap-
propriate indication in the [TT] box.
1. Left-click the [CPA/TCPA] indication to activate
the feature.
2. Place the cursor on the indication you wish to
adjust.
3. Left-click, or spin the scrollwheel, to adjust the settings as required. The settings
options are outlined in the table below.
Indication Method Settings options
CPA Left-click 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0 (NM)
Scrollwheel 0.1 to 20; 0 to 10 in 0.1 NM increments, 1 NM incre-
ments thereafter
TCPA Left-click 1, 2, 3, 4, 5, 6, 12, 15 (minutes)
Scrollwheel 1 to 60 minutes in 1-minute increments
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.
CPA setting
TCPA setting
Left-click here to activate
CPA/TCPA settings.
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