Unnecessary Echoes - Furuno FSV-35 Operator's Manual

2.22.2

Unnecessary echoes

Sea surface reflections
To reduce sea surface reflections, set the tilt angle to 4° or higher, so the upper edge
of the sonar beam does not hit the sea surface, or adjust TVG. When a decreased tilt
is used, sea surface reflections cover a large area as illustrated below.
Tilt: 0 °
Tilt: 4 ° -5 °
10 °
Wake
A wake produced by own ship or another ship can be a strong reflecting object when
a decreased tilt angle is used. As the wake appears as a thick continuous line, it can
be easily distinguished from a school of fish. A wake contains many air bubbles which
attenuate ultrasonic energy, making it difficult to sound beyond the wake.
Other
ship
Own
ship
Sea surface
10 °
Sea surface
Own ship's
screw noise
Wake produced
by other ship
2. HORIZONTAL MODE
Tilt angle
indication
Sea surface
reflections
Own ship's wake
Own ship's
(produced when
screw noise
own ship turned)
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