Raymarine a series Installation And Operation Instructions Manual page 192

There are conditions where acquiring a target may become
difficult. These same conditions may be a factor in successfully
tracking a target. Some of the conditions are:
• The target echo is weak. The target is very close to land,
buoys or other large targets.
• The target or your own vessel is making rapid manoeuvres.
• Choppy sea state conditions exist and the target is buried in
excessive sea clutter or in deep swells.
• Choppy sea state conditions exist yielding poor stability; own
vessel's heading data is very unstable.
• Inadequate heading data.
Symptoms of such conditions include:
• target acquisition is difficult and the MARPA vectors are
unstable;
• the symbol wanders away from the target, locks-on to another
target, or changes to a lost symbol target.
In these circumstances, target acquisition and tracking may
need to be re-initiated and in some cases might be impossible
to maintain. Better quality heading data might improve
performance in these circumstances.
How a MARPA risk is assessed
Each target is monitored to ascertain whether it will be within a
certain distance from your vessel within a certain time. If so, the
target is designated as dangerous, and an audible warning is
sounded and a warning displayed. The target symbol changes
to the dangerous target symbol and flashes to indicate that it is
a dangerous target. Acknowledging the alarm will remove the
warning.
If a target is lost, either because the MARPA software has
lost contact 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.
Acknowledging the warning will silence the alarm and remove
the on-screen warning and the target lost symbol.
Effective range for MARPA targets
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 radar scanner and will be lost. In such cases,
an on-screen warning indicates that the target is off-screen.
MARPA context menu
The MARPA function includes a context menu which provides
positional data and menu items.
The context menu provides the following target information:
• CPA
• TCPA
• COG
• SOG
The context menu also provide the following menu items:
• Cancel target
• CPA Graphic
• MARPA Data
• Slew thermal camera (Only available when thermal camera
is connected and operating.)
192
Accessing the context menu
You can access the context menu by following the steps below.
1. Non-touchscreen and HybridTouch displays:
i. Selecting a location, object or target on-screen and
pressing the Ok button.
2. HybridTouch and Touch only displays:
i. Selecting an object or target on-screen.
ii. Selecting and holding on a location on-screen.
Configuring MARPA options
From the radar application:
1. Select Menu.
2. Select Track Targets.
3. Select MARPA Options or MARPA & AIS Options.
4. Select Vector Length.
5. Select an appropriate time period.
The distance that your vessel travels in the time period you
specify here determines the length of the vector lines.
6. Select Target History.
7. Select an appropriate time period.
The target's previous position will be plotted on the radar
display as a target icon with lighter shading than the actual
target.
Note: MARPA and AIS functions share Safe Zone and
Vector Length settings.
Showing the Safe Zone Ring
To show the Safe Zone ring follow the instructions below:
From the Chart or Radar application:
1. Select Menu.
2. Select Presentation.
3. Select Overlays.
4. Select Safe Zone Ring so that Show is highlighted.
Selecting Safe Zone Ring will switch the zone ring between
hidden to visible.
Setting up the Safe Zone Ring
You can adjust the Safe Zone Ring radius, the time to Safe Zone
and choose whether AIS targets trigger the Safe Zone alarm
from the Safe Zone Ring Set-up menu.
The Safe Zone Set-up menu can be accessed as follows:
• From the Radar application: Menu > Track Targets > Safe
Zone Set-up
• From the Chart application with only the AIS overlay enabled:
Menu > AIS Options > Safe Zone Set-up
• From the Chart application with only the Radar overlay
enabled: Menu > Radar Options > Track Targets > Safe
Zone Set-up
• From the Chart application with the AIS and Radar overlays
enabled: Menu > Radar & AIS Options > Track Targets >
Safe Zone Set-up
From the Safe Zone Set-up menu:
1. Select Safe Zone Radius.
i. Select the required radius for the safe zone.
2. Select Time to Safe Zone.
i. Select the required time period.
3. Select AIS Alarm so that On is highlighted.
Selecting AIS Alarm will switch the dangerous target alarm
between On and Off.
Using MARPA
Acquiring a MARPA target to track
From the radar application:
1. Select the target to be acquired.
The MARPA context menu is displayed.
2. Select Acquire Target.
The "target being acquired" symbol is displayed. If the target is
present for several scans, the radar locks-on to the target, and
the symbol changes to "safe target" status.
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