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AP-7
TCPA is the time to CPA measured with
present speeds of own ship and the targets.
Both CPA and TCPA are automatically cal-
culated. When a target ship has passed clear
of own ship, the CPA is displayed and the
TCPA appears as "**.*". TCPA is counted up
to 99.9 min. and beyond this it is indicated as
TCPA>99.9 min.
Mode and length of Vectors
True or Relative Vector
Target vectors are displayed in relative or true
mode. Own ship does not have a vector in rela-
tive mode.
Vector Length
From the ARP-10 MENU, Vector Length can
be set to 30 seconds, 1, 3, 6, 15 or 30 minutes
and the selected vector time is indicated on
the screen.
The vector tip shows an estimated position of
the target after the selected vector time
elapses. It can be valuable to extend the vec-
tor length to evaluate the risk of collision with
any target.
Past position Display
The Auto Plotter displays equally time-spaced
dots (maximum 5 dots) marking the past po-
sitions of any targets being tracked.
If a target changes its speed, the spacing will
be uneven. If it changes the course, its plotted
course will not be a straight line in TM mode.
Operational Warnings
There are two main situations which cause the
Auto plotter to trigger visual and audible
alarms.
• CPA/TCPA alarm
• Lost target alarm
CPA/TCPA Alarm
Visual and audible alarm are generated when
the predicted CPA and TCPA of any target
become less than their preset limits. The au-
dible alarm continues for 10 seconds.
The Auto plotter ARP-10 continuously moni-
tors the predicted range at the Closest Point
of Approach (CPA) and predicted time to CPA
(TCPA) of each tracked target to own ship.
When the predicted CPA of any target be-
comes smaller than a preset CPA alarm range
and its predicted TCPA less than a preset
TCPA alarm limit, the ARP-10 releases an
audible alarm. In addition, the target plot sym-
bol changes to a triangle and flashes together
with its vector.
Provided that this feature is used correctly, it
will help prevent the risk of collision by alert-
ing you to threatening targets. It is important
that GAIN, A/C SEA, A/C RAIN and other
radar controls are properly adjusted and the
Auto Plotter is set up so that it can track tar-
gets effectively.
CPA/TCPA alarm ranges must be set up prop-
erly taking into consideration the size, ton-
nage, speed, turning performance and other
characteristics of own ship.
WARNING
The CPA/TCPA alarm feature should
never be relied upon as a 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.
Follow the steps shown below to set the CPA/
TCPA alarm ranges:
1. Open the "ARP-10 MENU".
2. On the "CPA Set" line, select a CPA limit
desired. (Off, 0.5, 1, 2, 3, 5, 6 nm)
3. Press the [ACQ/ENTER] key.