Reference Manual Part 2

G-Series Reference Manual 152
MARPA
The Mini Automatic Radar Plotting Aid (MARPA) provides target-
tracking and risk-analysis features. MARPA obtains detailed infor-
mation for up to ten automatically tracked objects and provides
continuous, accurate and rapid situation analysis.
To use MARPA, you need a fast heading sensor.
Setting up MARPA
You can customize the following parameters from the MARPA
Options menu:
To open the MARPA Options menu
1. Press the TARGET TRACKING softkey.
2. Press the MARPA & AIS OPTIONS softkey.
3. Change MARPA options as required.
Safety notices
MARPA can improve collision avoidance when used wisely. It
is the User’s responsibility to exercise common prudence and
navigational judgements.
There are certain conditions under which acquiring a target may
become difficult. Some of those conditions are:
• The target echo is weak.
• The target is very close to land, buoys or other large targets.
• The target or your own ship is making rapid manoeuvres.
• Choppy sea state conditions exist and the target is buried in ex-
cessive sea clutter or in deep swells.
• Choppy sea state conditions exist yielding poor stability.
• Inadequate heading data exists.
Symptoms of such conditions are that acquisition is difficult and the
MARPA vectors are unstable; the symbol wanders away from the
target, locks on to the wrong target or changes to a lost symbol
target.
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.
To acquire a target
MARPA automatically tracks acquired targets, calculates target
bearing and range, speed and course, Closest Point of Approach
(CPA), and Time to Closest Point of Approach (TCPA).
Parameter Options
Vector Length
The time period specified for drawing
length of vectors.
0.5min, 1 min, 3 min, 6min,
12min, 30 min, 60 min
Target History
Plots a target’s previous position at the
specified intervals. The four most recent
position points are displayed. If True
target vectors are selected, the four most
recent vessel position points are also
displayed.
OFF, 0.5 min, 1 min, 3 min, 6 min
Own vessel safe zone
The safe zone is a ring, centred on your
boat, within which a target is considered
dangerous if it will enter this zone within
the time to safe zone period.
0.1 nm, 0.2nm, 0.5nm, 1.0 nm,
2.0nm
Time to safe zone
If a target enters your safe zone within this
time period, it is considered dangerous.
3 mins, 6 mins, 12 mins, 24 mins
Safe zone ring
Controls whether the safe zone ring is
displayed or hidden on screen
Visible
Hidden