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7. FISH FINDER (SOUNDER)
7-22
Size of a school of fish
Usually the size of fish echoes on the screen is proportional to the actual size of the
school of fish. However, if two fish echoes appear at different depths with the same
size, the school of fish at the shallower depth is larger because the ultrasonic beam
widens as it propagates and a school of fish in deep water is displayed larger.
Density of a school of fish
If two schools appear with the same color at different depths, the one in deeper water
is denser because the ultrasonic wave attenuates as it propagates and the school of
fish in deep water tends to be displayed in a weaker color.
Bottom fish
The echoes from the bottom are stronger than the
bottom fish echoes so that you can distinguish be-
tween them by colors. The bottom echoes are
normally shown in reddish-brown or red, the bot-
tom fish echoes in weaker color.
Sounding time for a deep school of fish
p
school
o
e for a deep
e
f
or
S
g
S
o
un
di
ng
tim
e
Sounding time for a shallow school of fish
Sounding time for a shallow school of fish
School depth and sounding time
Fish echo
Weak echo
Less reddish
(Sparse echo)
Reddish
(Dense echo)
a
k
ec
h
o
o
Strong echo
Difference in signal strength
Bottom fish echo