Chapter 4: Fishfinder Operations 4-3
Bottom Indications
Effect of Frequency and Boat Speed
The return from a fish has a different appearance depending on the frequency
used: 50kHz produces a wide beam, so a fish spotted by this frequency gives a
broad arch; the 200 kHz beam is narrower so the same fish produces a
narrower arch.
The shape of the arch is also affected by the speed of the boat. If the boat is
moving slowly, the arches tend to be longer; if the boat is moving more
quickly, the arches are short and peaked. If the boat is moving very fast, a fish
may be indicated by a single vertical line.
In Bottom lock mode the fish arches may appear distorted as the bottom
topography is removed from the image.
Bottom Indications
The bottom usually produces a strong echo, so it is easy for the Fishfinder to
see a lot of detail. The Fishfinder can indicate many different kinds of bottom
conditions.
As illustrated in Figure 4-2, a hard bottom appears as a thin line.
Figure 4-2: Fishfinder Bottom Indications
D5016-2
A
Hard bottom (sand)
B
Soft bottom (mud)
C
Rocky bottom
D
White line feature on:
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