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2.4.4
Tilt angle for surface fish
Sound emitted from the sonar transducer forms an
oval-shaped beam with a width of approximately
10° for 80kHz and 13° for 70kHz in the vertical di-
rection (vertical beam width at -6dB). The tilt angle
indicates the angle between the centerline of the
beam and the horizontal plane. Then, if the tilt an-
gle is set to 0°, the centerline 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 reflections. When the sea is calm, since the
sound is reflected just like a light hitting a mirror at a low incident angle, it propagates
away and the sea surface reflections become negligible.
However if the sea is not calm enough, they will become dominant and interfere with
observation of wanted echoes. To minimize these sea surface reflections and to
search for schools of fish on the surface effectively, the tilt angle is usually set between
4° and 5° so the upper portion of the beam becomes almost parallel with the sea sur-
face. When the sea is rough, the tilt angle is slightly increased to lessen the affect of
sea surface reflections.
2.4.5
Suitable tilt angle
The figure below illustrates the relationship among tilt angle, depth and detection
range. Refer to it to find out the suitable tilt angle for a given depth/detection range.
Tilt angle setting: relationship between tilt angle and detection range
(200)
20(40)
40(80)
60(120)
80(160)
100(200)
200(400)
Vertical width of sonar beam
100 m
100 m
10°
100
200
(400)
200 m
10 m
20 m
Tilt Angle 0°
Tilt Angle 4° to 5°
400
300
(800)
(600)
300 m
30 m
2. SLANT MODE
Sea Surface
6°
Sea Surface
6°
Range(m)
Tilt angle
(0° to 3°)
Tilt angle
(2° to 8°)
Tilt angle
(7° to 13°)
shown in gray
Tilt angle
(12° to 18°)
2-7
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