NorthStar EXPLORER 443D, Installation And Operation Manual

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4-1 Interpreting the display
The sonar displays do not show a fixed distance
travelled by the boat; rather, they display a
history, showing what has passed below the boat
during a certain period of time.
The history of the sonar signal displayed 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 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 600ft it takes about 2.5 minutes
for each vertical line of pixels 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 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
covered 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
bottom.
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 Explorer 443d/443df
This section explains how to interpret the sonar
displays, when and why to use the different
frequencies and how fish are detected
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 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 Explorer 443d/443df
works.
Northstar Explorer 443d/443df Installation and Operation Manual 17