Furuno GP-3700F, Operator'S Manual

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11-1
11. ECHO SOUNDER
11.1 How the Echo Sounder Operates
The echo sounder calculates the distance between its transducer and underwater ob-
jects like fish, lake bottom or seabed. The results are shown in different colors or
shades of gray according to echo strength.
The ultrasonic waves transmitted through water move at a constant speed of approx-
imately 4800 feet (1500 meters) per second. When a sound wave “hits” an underwater
object like fish or sea bottom, part of the sound wave is reflected toward the source.
To find the depth to an object, the echo sounder calculates the time difference be-
tween the transmission of a sound wave and the time the reflected sound wave is re-
ceived.
The picture displayed by the echo sounder contains a series of vertical scan lines.
Each line is a "picture" of the objects under the boat. The series of pictures are put
side-by-side across the screen to show the contours of the bottom and echoes from
fish. The amount of history of objects that have moved under the boat can be less than
a minute to more than one minute depending on the picture advance speed.
Note: Unless otherwise noted, the following procedures assume the echo sounder
screen is displayed. The menu items for the echo sounder are only accessible when
the echo sounder screen is displayed.
11.2 Echo Sounder Displays
The echo sounder is displayed in full screen or combination with the plotter screen.
There are nine display modes as below:
For the display setting, see section 1.4.
• Single frequency display • Dual frequency display
• Marker zoom display • Bottom zoom display
• Bottom lock display
• A-scope display • Bottom discrimination display (seabed
composition)
• Plotter/echo sounder display • Mix display