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Standard range scales
Standard ranges that can be selected are shown in the following table:
Maximum range (nm)
*The maximum range depends on scanner type.
The number of range rings shown in the table is the number to the selected range.
Additional range rings are displayed to the edge of the radar picture, at the standard
ring interval for the current range, and are visible when the center is offset.
Interpreting the radar picture
Navigational echoes may be large, small bright or faint, depending not only on the size
of the object but also on its orientation and surface. Different objects reflect the radar
signals in different ways. For example, vertical objects such as cliffs reflect signals
better than sloping ones such as sandbanks.
High coastlines and mountainous coastal regions can be observed at the longest radar
range. However, the first sight of land may be a mountain several miles inland from the
coastline. The actual coastline may not appear on the radar until the boat is close to the
line of sight distance.
The radar indication may not be similar to your visual observation; a nearby small
object may appear to be the same size as a distant large object on the radar. However,
with experience the approximate size of different objects can be determined by the
relative size and brightness of the echoes.
Some targets, such as buoys and small boats, can be difficult to differentiate, since they
bob and toss about in the waves and do not represent a consistent reflecting surface.
Consequently, these echoes have a tendency to fade and brighten, and at times, to
Number of range rings (nm)
0.125
0.25
0.5
0.75
1.5
3
6
12
24*
48*
72*
Range ring interval (nm)
2
2
4
3
6
6
6
6
6
6
6
123
0.0625
0.125
0.125
0.25
0.25
0.5
1
2
4
8
12
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