Interpreting The Display - Navman TRACKFISH 6600 Installation And Operation Manual

8-2 Interpreting the display

The sonar displays do not show a fi xed 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 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 2 minutes for the data to move
across the display, whereas at 20 ft (6 m) it
takes only about 25 seconds.
The scroll speed can be set by the user to
display either a longer history with less fi sh
information or a shorter history with more fi sh
details (see section 15-3).
If the boat is anchored, the echoes all come
from the same area of bottom. This produces
a fl at bottom trace on the display.
The screen shot shows a typical sonar display
with the Fish symbols turned Off.
34
Strength of echoes
The colours indicate differences in the strength
of the echo. The strength varies with several
factors, such as the:
Size of the fi sh, school of fi sh or other object.
•
Depth of the fi sh or object.
•
Location of the fi sh 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.
Single fi sh
Large
school of
fi sh
Small
school of
fi sh
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
refl ect the pulse, resulting in a strong echo.
Bottom
See section 9-3.
NAVMAN
TRACKFISH 6600 Installation and Operation Manual
Kelp / Weed
Soft bottoms
such as mud,
weed and
sand show
as narrow
bands
Hard
bottoms
such as
rock or coral
show as
wide bands