Teleflex TFX320 Operation Manual page 11

The 320 displays structure such as
submerged grass, brush, trees and
wrecks on the bottom. Structure can
be distinguished by comparing the
area just above and below the main
bottom return. Usually structure
shows as areas of dark to light gray
on top of a dark bottom contour.
The appearance of structure is
greatly affected by boat speed and
direction; to repeat the same image
it is often necessary to travel the
same speed and direction over the
location where the structure was
originally located.The 320 is also
capable of showing layers of water having different temperatures. These
temperature differences, called thermoclines, appear at different depths,
depending on current conditions. A thermocline typically appears as a
continuous band of many gray levels moving across the display at the same
depth. Thermoclines always appear above the bottom.
Schools of bait fish as well as individual fish
are clearly visible on the 320 display. Bait fish
appear as "clouds" having different shapes
and sizes depending on the number of fish
and boat speed. Individual fish appear as
smaller black and gray lines often appearing
as a "fish arch." A fish arch forms as the fish
moves through the sonar beam. Due to the
transducer beam angle the distance to the
fish decreases as it moves into the beam, and then increases as it moves out.
When the chart window graphs this distance change, an arch appears. Boat
speed, the Chart Speed setting and movement of the fish greatly affect the
shape of the arch. When moving slowly, a fish creates an elongated arch. When
moving fast the arch appears shorter. A partial arch forms when the fish does
not move through the entire cone angle. It is important to remember that
sonar cannot distinguish between a fish and some other object suspended in
the water. Regardless of the object the sonar detects, each may be drawn as
an arch.
USING THE 320 SERIES
CONTROL FUNCTIONS
Fish Arch Diagram
Bait fish
Fish Arch
Partial Fish
Arch
Structure
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