Raymarine Pathfinder GPS Receiver User Manual


 
Chapter 10: Working with radar 83
8. Click to return the EBL to a dotted line and retain the adjustment.
Note:
When using a VRM/EBL, you may want to turn off the range rings to
make the VRM/EBL easier to see.
The distance and bearing of the target is now shown in the VRM/EBL
databox. You will be able to tell in which direction the target is traveling by
watching how it moves in relation to the EBL. If it continues to travel
directly along the EBL, it indicates that it is on a possible collision course
with your boat - take the appropriate action.
To place the second VRM/EBL pair:
1. Click the
MORE
soft key on the VRM/EBL 1 soft key bar. The softkeys
for VRM/EBL 2 will be displayed.
2. Repeat steps 2 through 8 above. The VRM/EBL will be placed at a loca-
tion 2/3 of current range and a bearing of 330
o
.
Guard zones
Guard zones enable you to set up one or two sector or 360
o
zones
around
your boat. Any target entering this zoned area will cause a guard alarm to
sound.
Guard zones are fixed with respect to the ship’s heading marker (SHM,
moving as the SHM moves. They also move if you offset the center, or if
you change the range scale, so that the area you have marked is main-
tained. However, a guard zone only operates when the whole zone is
displayed on the screen, or could be displayed by off-setting the center. In
addition, a guard zone is inactive for 10 seconds after it is placed or re-
sized, to avoid inappropriate alarms during positioning.
Placing a guard zone
Placing and positioning guard zones on RayTech is quick and easy.
D6992_1
Guard zone 1, sector zone
(short-dashed line)
Guard zone 2, circular zone
(long-dashed line)
D8777_1
84 RayTech RNS V6.0 - Users Guide
1. Click the
TARGET TRACKING
soft key.
2. Click
MONITOR IN ZONES
.
3. Click
Guard Zone 1
to ON
.
The default zone is displayed.
The default zone is a sector, 30
o
either side of the SHM, between 1/3
and 2/3 of the current range.
4. Click Set Up Zone 1. The set up soft keys are displayed.
You now have the option of setting a sector or circular guard zone
using the following soft keys:
Zone shape - enables you to choose sector or circle.
Set inner - enables you to set the distance of the inner edge of the
zone from your boat.
Set outer - enables you to set the distance of the outer edge of the
zone from your boat.
Set width - enables you to set the width of a sector zone each side
of the SHM.
Set bearing - enables you to set the bearing of the zone from your
boat.
Note:
The same procedures are used for setting up Guard Zone 2. The
default zone is the same as Guard Zone 1.
10.10 MARPA
Safety Notices
CAUTION: MARPA can improve collision avoidance when used
wisely. It is the user’s responsibility to exercise common
prudence and navigational judgement.
There are conditions where acquiring a target may become difficult. These
same conditions may be a factor in successfully tracking a target. Some of
these conditions are:
The target echo is weak. The target is very close to land, buoys or other
large targets.
The target or your own boat is making rapid maneuvers.
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 boat’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 on to 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.
What is MARPA?
You can use the Mini Automatic Radar Plotting Aid (MARPA) functions for
target tracking and risk analysis. MARPA improves collision avoidance by
obtaining detailed information for up to 10 automatically tracked targets
and provides continuous, accurate and rapid situation evaluation.
MARPA automatically tracks acquired targets, calculates target bearing
and range, true speed and course, Closest Point of Approach (CPA) and
Time to Closest Point of Approach (TCPA).
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