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CA42/50/52 Echosounder operation Chapter 7
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7. Echosounder operation
The echosounder function of the CAXX determines the distance
between its transducer and underwater objects such as fish, lake bottom
or seabed. It does this by utilizing the fact that an ultrasonic wave
transmitted through water travels at a nearly constant speed of 4800 feet
(1500 meters) per second. When a sound wave strikes an underwater
object such as fish or sea bottom, part of the sound wave is reflected
back toward the source. Thus by calculating the time difference between
the transmission of a sound wave and the reception of the reflected
sound wave, the depth to the object can be determined.
The entire process begins in the display unit. Transmitter power is sent
to the transducer as a short pulse of electrical energy. The electrical
signal produced by the transmitter is converted into an ultrasonic signal
by the transducer and transmitted into the water. Any reflected signals
from intervening objects (such as a fish school) are received by the
transducer and converted back into an electrical signal. It is then ampli-
fied in the amplifier section, and finally, displayed on the screen.
The picture displayed is made up of a series of vertical scan lines
(pings), one for each transmission. Each line represents a ‘snapshot’ of
what has occurred beneath the boat. The series of snapshots are accumu-
lated side by side across the screen, and the resulting contours of the
bottom and fish between the bottom and surface are displayed.
Selecting echosounder displays
The CAXX provides four types of echosounder displays: standard, bot-
tom zoom, marker zoom and A-scope. Each display has its advantages
and disadvantages. Select the appropriate setup for the echosounder
display in the presentation ‘Setup’ and ‘Echosounder setup’ displays,
considering current sea area and target fish.
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To view the echo display while plotting ship’s route, select a CHART
display in one window and an ECHO display in the adjacent window.