Section Three: On The Water; Understanding Sonar - Garmin Fishfinder 320C Owner's Manual And Reference Manual

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If you are unfamiliar with basic sonar, or need help determining what is displayed on the graph, this

section may be for you. This section is intended to help the novice user gain some understanding of how the

Fishﬁ nder 320C operates and how it can help improve their ﬁ shing productivity.

To understand what the unit is displaying, it is important to have a general knowledge of how the unit

works and how it determines what to display. Brieﬂ y described, the unit operates by transmitting sound

waves toward the bottom of a lake, stream, or seabed in a cone-shaped pattern. When a transmitted sound-

wave strikes an underwater object such as the bottom, a piece of structure, or a ﬁ sh, sound is reﬂ ected back

to the transducer. The transducer collects the reﬂ ected sound waves and sends the data to the unit to be

processed and displayed on the graph. The underwater data is displayed on the graph in the order that it is

returned: ﬁ rst returned—ﬁ rst on the graph. The diagram below demonstrates this by showing an underwa-

ter scene as it would be displayed on the graph. Generally speaking, if the only thing between the transducer

and the bottom is water, the ﬁ rst strong return will come from the bottom directly below the transducer. The

ﬁ rst strong return sets the bottom level. Weaker secondary returns provide the detailed data. Sonar returns

will display as reds (strongest), then oranges (strong), yellows (medium), greens (weaker) and blues (weak-

est).

That is a brief description of how your Fishﬁ nder 320C operates. The following pages will show how

this data can help you to improve your ﬁ shing.

This ﬁ sh is currently in a dead zone and is not

detected by the sonar. The ﬁ sh is in the coverage

area of the transducer, but remember– the ﬁ rst

strong return sets the bottom level. The ﬁ sh will

eventually be detected when the ﬁ rst strong return

sets the bottom level below the ﬁ sh.

On the Water

Understanding Sonar

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