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Tilt angle for surface fish
Sound emitted from the sonar transducer forms a circle-shaped
beam with a width of approximately 12 degrees in the vertical
direction (vertical beam width). The tilt angle is indicated by the
angle between the center line of the beam and the horizontal
plane. Then, if the tilt angle is set to 0 degrees, the center line is
parallel with the sea surface and one half of the emitted sound
goes upward, toward the sea surface.
This causes one half of the emitted sound to be reflected toward
the transducer and displayed on the screen as sea surface reflec-
tions. When the sea is calm, since the sound is reflected just like
a light hitting a mirror at a narrow incident angle, it propagates
away and the sea surface reflections become negligible.
However if the sea is not calm enough, they will become domi-
nant and interfere with observation of wanted echoes. To mini-
mize these sea surface reflections and to search surface fish
schools effectively, the tilt angle is usually set between 5 and 6
degrees so the upper portion of the beam becomes almost paral-
lel with the sea surface. When the sea is rough, it is often set to a
little larger angle.
Tilt angle 0°
Surface
Tilt angle 5-6°
Surface
12°
12°
Figure 2-2 Tilt angle and sea surface reflections