Furuno FSV-85, Operator'S Manual

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2. HORIZONTAL MODE
2-8
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° in the vertical direction (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 angle 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 0
°
Sea surface
Tilt angle 4-5
°
Sea surface
10
°
10
°
Range(m)
Vertical width of sonar beam
Depth (m)
Tilt angle setting: relationship between tilt angle and detection range
(-6dB)
100
(200)
200
(400)
300
(600)
400
(800)
Tilt 0
°
(0°-5°)
20(40)
40(80)
60(120)
80(160)
100(200)
200(400)
10
°
17 m
100 m 100 m
300 m
52 m
200 m
35 m
Tilt 5
°
(0°-10°)
Tilt 15
°
(10°-20°)
Tilt 10
°
(5°-15°)
In grey