NorthStar Navigation EXPLORER 657 Fish Finder User Manual


 
33Northstar Explorer 657 Installation and Operation Manual
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.
A
C
D
B
A Single fish
B Large school of fish
C Small school of fish
D Bottom
A Kelp / Weed
B Soft bottoms such as mud, weed and sand
show as narrow bands
C Hard bottoms such as rock or coral show as
wide bands
A
C
B
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
The sonar pulse
generated by the 657
transducer travels down
through the water,
spreading outwards in
a cone shape. The cone
width is dependent
upon the frequency of
the pulse; at 50 kHz it
is approximately 45°,
and at 200 kHz it is
approximately 11°.
The differences in the
cone width affect what is
displayed. See
section 8-3.