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PLUS Series LCD Display
Introduction to
MARPA
• Choppy sea state conditions exist yielding poor stability; own ship’s
heading data is very unstable.
• Inadequate heading data
Symptoms of such conditions are that acquisition is difficult and the
MARPA vectors are unstable; the symbol wanders away from the target,
locks onto another target or changes to a lost target symbol. If any of these
conditions are present, acquisition and tracking may need to be re-initiated
or, in some cases be impossible to maintain. Improving the quality of the
heading data will reduce the effect of the other conditions.
Risk Assessment
Each target is monitored to see if it will be within a certain distance from your
own vessel within a certain time. If so, the target is designated as dangerous
and you are warned with an audible alarm in addition to a warning on the
screen. The target symbol changes and flashes to indicate that it is a dangerous
target. Pressing any key silences the alarm and removes the warning, but the
target symbol remains dangerous.
Both the distance (Own Vessel Safe Zone) and the time (Time to Safe Zone)
are selectable as described in Section 7.5.
If a target is lost, either because the MARPA software has lost contact with it,
or because it has moved out of range, you are warned, again with an audible
alarm and an on-screen warning. Pressing any key silences the alarm, removes
the warning and removes the lost target symbol from the screen.
Target Data
All MARPA targets are stored in a MARPA database list, which shows
bearing, range, course and speed of each tracked target.
For any one target a pop-up data box can be placed on the screen, this shows
bearing, range, course, speed, CPA (Closest Point of Approach) and TCPA
(Time to Closest Point of Approach). The target for which data is displayed is
indicated by a circle around its symbol.
Each target is displayed as a symbol to indicate its status:
Target is being acquired
Target is safe
Target is dangerous.
Target is Lost
The dangerous and lost symbols are shown flashing.
81186_2.book Page 24 Monday, December 17, 2001 8:35 AM