4-1 Interpreting the display

The sonar displays do not show a fixed dis tance
travelled by the boat; rather, they display a
history, showing what has passed bel ow the
boat during a certain period of time .
The history of the sonar signal disp layed
depends on the depth of the water and the
scroll speed setting.
In shallow water, the echoes have a short
distance to travel between the botto m and the
boat. In deep water, the history moves across
the display more slowly because the e choes
take longer to travel between the bot tom and
the boat. For example, when the scroll sp eed is
set to Fast, at depths over 600ft it takes abou t
2.5 minutes for each vertical line of pixe ls to
move across the display, whereas at 20ft it
takes only about 4-5 seconds.
The scroll speed can be set by the user to
display either a longer history wi th less fish
information or a shorter history w ith more fish
details. See section 3-2 Setup > Son ar.
If the boat is anchored, the echoes all co me
from the same area of bottom. This pro duces a
flat bottom trace on the display.
The screen shot shows a typical so nar display
with the Fish symbols turned Off.
Large
school of
fish

Strength of echoes

The colors indicate differences in th e strength
of the echo. The strength varies with seve ral
factors, such as the:
• Size of the fish, school of fish or other object.
• Depth of the fish or object.
• Location of the fish or object. ( The area
covered by the ultrasonic pulse is a rough
cone shape and the echoes are stronges t in
the middle.)
• Clarity of water. Particles or air in the water
reduce the strength of the echo.
• Composition or density of the o bject or
bottom.
Note: Planing hulls at speed produce air bubbl es
and turbulent water that bombard the transducer.
The resulting ultrasonic noise may be picked up by
the transducer and obscure the real echoes.
4 Using the FISH 4432/4433
This section explains how to interpre t the sonar
displays, when and why to use the differ ent
frequencies and how fish are detec ted
and displayed.
Single fish
Hard bottoms
such as rock
or coral
show as wide
bands
Soft bottoms
such as mud,
weed and
sand show
as narrow
bands

Bottom types

Mud, weed and sandy bottoms tend to weake n
and scatter the sonar pulse, resultin g in a weak
echo. Hard, rocky or coral bottoms r eflect the
pulse, resulting in a strong echo. See s ection
5-3 Sonar Bottom display.
Small school
of fish
Bottom
It also describes Gain and Range and s hows
examples of some of the differen t sonar
displays. Also see section 1-2 How the FISH
4432/4433 works.
FISH 4432/4433 Installation and Operation Manual17 NAVMAN