Furuno FSV-30 Operator's Manual page 78

2. HORIZONTAL MODE
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˚
Tilt: 5-6˚
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.
Own
ship
2-48
Sea surface
18˚
Sea surface
18˚
Sea surface reflections
Other
ship
Own ship's
screw noise
Wake produced
by other ship
Own ship's
screw noise
Wake
Tilt angle
indication
Sea surface
reflections
Own ship's wake
(produced when
own ship turned)