Raymarine RayTech RNS 5.0 User Manual page 64

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Each tracked target can be displayed with a vector depicting approximate target speed
(vector length) and course (vector direction). The target data can be displayed on-
screen in the MARPA Target databox, each target is continually assessed, and you are
warned if one becomes dangerous or is lost.
Effective MARPA operation is dependent on the accuracy of your own ships heading
data, plus Speed over Ground (SOG) and Course Over Ground (COG). The better the
quality of the heading data, the better MARPA will perform. MARPA will function
without SOG and COG data, but only relative vector, CPA and TCPA are shown; target
course and speed cannot be calculated.
How is a risk assessed?
Each target is displayed as a symbol to indicate its status:
Each target is monitored to determine if it will be within a certain distance from your
own boat within a certain time. If so, the target is designated as dangerous, and you
are notified with an audible alarm and a flashing on-screen 'MARPA target (ID No.)
Dangerous' warning. Press any key to cancel the alarm and remove the warning;
however, the target is dangerous symbol remains displayed. Both the distance (Own
Vessel Safe Zone) and the time (Time to Safe Zone) are selectable.
If a target is lost, it is either because the MARPA software has lost contact with it, or it
has moved out of range. If this occurs, you are notified with an audible alarm and an
on-screen 'MARPA target (ID No.) lost' warning. Press any key to silence the alarm and
remove the message and lost target symbol from the screen.
How far from my boat does MARPA work?
MARPA target acquisition is only available at radar range scales of up to 12 nm,
although tracking continues at all ranges.
If you change to a smaller range scale, targets may be beyond the range of your
scanner and will be lost. In such cases, an on-screen warning will indicate that the
target is off-screen.
Target is being acquired
Target is safe
Target is dangerous
Target is lost
RayTech RNS V5.0 - User's Manual