Furuno FSV-24 Operator's Manual page 69

Sea surface reflections
To reduce sea surface reflections, set the tilt angle to 5 or higher, so the upper
edge of the sonar beam does not hit the sea surface, or adjust TVG. When a
decreased tilt angle is used, sea surface reflections cover a large area as
illustrated below.
Tilt: 0˚ 12˚
Tilt: 5-6˚
12˚
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 fish school. A wake contains many air
bubbles which attenuate ultrasonic energy, making it difficult to sound beyond
the wake.
Other
ship
Own
ship
Own ship's
screw noise
Sea surface
Sea surface
Figure 2-52 Sea surface reflections
Wake produced
by other ship
Figure 2-53 Wake
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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