How to Obtain a RADAR Bearing and Range
The PPI is equipped with a bearing cursor and a range strobe. The
bearing cursor, like the sweep, appears as a bright line and can be
manually rotated through 360°. Bearing information is obtained by
rotating the cursor to the center of the target. The target bearing is then
read directly from the bearing dial. On gyro-equipped ships (and most
ships having radars are so equipped), the radar has a gyro input and
bearings obtained from it are true. If a gyro failure occurs the radar
presentation automatically re-orients to a relative picture and relative
bearings may be taken from the PPI.
The range strobe appears as a bright spot riding on the cursor. As the
range crank is turned clockwise, the strobe moves out from the center.
Range is obtained by placing the strobe on the leading edge (edge
closest to the center of the PPI) of the target. The target range is then
read directly from the range dials, either in miles or yards.
When plotting a radar fix, you will have already been comparing your
radar "picture" with the navigational chart. Pick out points that show
prominently on both the chart and the radar. Try to locate reliable
targets that are easy to identify. You cannot afford to guess on what
you are using to obtain a range from. Objects not permanently fixed to
shore or the ocean bottom such as buoys should not be used when
obtaining a radar fix. Tangents also should be used as a last resort.
The order in which you take your radar ranges is just as important as it
in Proper Order
was in visual bearings. Take radar ranges ahead and astern first because
they are changing most rapidly, then take ranges on or near the beam.
As is true with visual fixes, time is a critical element. Work quickly,