Operation Manual

8120 Installation and Operation Manual34
CAUTION
!
!
CAUTION
DANGER
WARNING
Bottom types
Mud, weed and sandy bottoms tend to
weaken and scatter the sonar pulse, resulting
in a weak echo. Hard, rocky or coral bottoms
reflect the pulse, resulting in a strong echo.
Frequency and cone width
Water Cone width Cone width
Depth at 50 kHz at 200 kHz
25 20 5
50 40 10
100 80 20
150 130 30
200 170 40
300 250 60
400 330 80
600 500 120
800 660 150
1000 830 190
45° cone
11°
cone
Strength of echoes
The colours indicate differences in the
strength of the echo. The strength varies with
several factors, such as the:
• Size of the fish, school of fish or other
object.
• Depth of the fish or object.
• Location of the fish or object. (The area
covered by the ultrasonic pulse is a rough
cone shape and the echoes are strongest
in the middle.)
• Clarity of water. Particles or air in the water
reduce the strength of the echo.
• Composition or density of the object or
bottom.
Planing hulls at speed produce air bubbles
and turbulent water that bombard the
transducer. The resulting ultrasonic noise
may be picked up by the transducer and
obscure the real echoes.