Navman FISH 4500/4600 - Manual (Page 15)

4-1 Interpreting the display
The sonar displays do not show a fixed distance
travelled by the boat; rather, they display a his-
tory, showing what has passed below the boat
during a certain period of time.
The history of the sonar signal displayed de-
pends on the depth of the water and the scroll
speed setting.
In shallow water, the echoes have a short
distance to travel between the bottom and the
boat. In deep water, the history moves across
the display more slowly because the echoes
take longer to travel between the bottom and the
boat. For example, when the scroll speed is set
to Fast, at depths over 1000 ft. (300 m) it takes
about 4 minutes for each vertical line of pixels
to move across the display, whereas at 20 ft. (6
m) it takes only about 15 seconds.
The scroll speed can be set by the user to display
either a longer history with less fish information
or a shorter history with more fish details. See
section 3-2 Setup > Sonar.
If the boat is anchored, the echoes all come from
the same area of bottom. This produces a flat
bottom trace on the display.
The screen shot shows a typical sonar display
with the Fish symbols turned Off.
Large
school of
fish
Strength of echoes
The colors indicate differences in the strength of
the echo. The strength varies with several 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 cov-
ered by the ultrasonic pulse is a rough cone
shape and the echoes are strongest in the
middle.)
• Clarity of water. Particles or air in the water
reduce the strength of the echo.
• Composition or density of the object or bot-
tom.
Note: Planing hulls at speed produce air bubbles
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 4500/4600
This section explains how to interpret the
sonar displays, when and why to use the dif-
ferent frequencies and how fish are detected
and displayed.
Single fish
Kelp / Weed
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 weaken
and scatter the sonar pulse, resulting in a weak
echo. Hard, rocky or coral bottoms reflect the
pulse, resulting in a strong echo. See section
5-3 Sonar Bottom display.
Small school
of fish
Bottom
It also describes Gain and Range and shows
examples of some of the different sonar displays.
Also see section 1-2 How the FISH 4500/4600
works.
FISH 4500/4600 Installation and Operation Manual 15 NAVMAN