Garmin Fishfinder 140 Owner's Manual - Understanding Sonar
Fishfinder 90/140 Owner’s Manual
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ETTING
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G
ETTING
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TARTED
To get the most out of your new Fishfinder:
• Before you install and use your Fishfinder, read and
learn the information in this manual.
• Assemble and install the hardware (page 4).
• Practice using your Fishfinder in simulator mode
(page 3).
• Use the Fishfinder (page 12).
Understanding Sonar
The transducer that you mount on your vessel sends
sound waves toward the bottom of the water in a cone-
shaped pattern. When a sound wave strikes an underwater
object (such as the bottom, a structure, or a fish), sound is
reflected back to the transducer. The transducer collects the
reflected sound waves and sends the data to the Fishfinder
to be processed and shown on the screen. The underwater
data is shown on the screen in the order that it is returned;
the first returned is the first on the screen.
Generally speaking, if the only thing between the
transducer and the bottom is water, the first strong return
comes from the bottom directly below the transducer,
and this sets the bottom level. Weaker secondary returns
provide the detailed data. Stronger returns appear in darker
hues.
Understanding the Fishfinder Screen
The transducer sends a beam down to the bottom of the
water, much like the beam of a flashlight. The beam starts
small near your vessel and expands as it gets to the bottom.
The Fishfinder screen does not display a three-dimensional
representation of the underwater environment; the screen
is in two dimensions, much like if you took a picture
of an aquarium. Only the depth of the item in the water
appears. The screen does not show you where an item is
located horizontally in the water, as shown in the following
drawings. The fish is not directly above the tree in reality,
but it might look like it is on the Fishfinder screen.