Reference Manual Part 2

153 Chapter 11: Radar
Each target tracked can be displayed with a CPA graphic which
shows the target vessel, course and speed (as a vector) and indi-
cates the CPA. The calculated target data can also be shown on
your screen. Each target is continually assessed and an audible
alarm is sounded if a target becomes dangerous, or is lost.
Effective MARPA operation is dependant on accurate own-ship’s
heading and speed. Speed Over Ground (SOG) and Course Over
Ground (COG) information are required to show true target course
and speed. The better the quality of the heading and speed data,
the better MARPA will perform. MARPA will function without SOG
and COG in relative mode. For the best heading data a Raymarine
SMART heading sensor or a gyro-stabilized autopilot is required.
Risk assessment
Each target is monitored to see if it will be within a certain distance
from your boat within a certain time. If so, the target is designated
as dangerous and an audible warning is sounded along with an on-
screen warning being shown. The target symbol changes to the
dangerous target symbol and flashes to indicate that it is a danger-
ous target. Pressing the appropriate soft key will silence the alarm
and remove the warning.
If a target is lost, either because the MARPA software has lost con-
tact with it, or because it has moved out of range, an audible alarm
is sounded and an on-screen warning appears. The on-screen
symbol will change to the target lost symbol. Pressing the appropri-
ate soft key will silence the alarm and remove the on-screen
warning and the target lost symbol.
MARPA range
MARPA target acquisition is only available at radar range scales of
up to 12nm, 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.
Closest point of approach
Closest point-of-approach (CPA) graphics show vectors for your
vessel and a selected target. (A vector is a line showing a predicted
course.) Vector length varies with speed (settings can be changed
in the MARPA Setup Menu).
To show or hide closest point-of-approach
1. Highlight the object with the cursor.
MARPA targets
D6810_4
D9008_1
Vector
CPA graphic
3 9