Section 6 Principal
89
SECTION 6
Principal
Figure 6-1
Sonar Basics
A Fish Finder is a device which transmits ultrasonic signals into the water
and listens for echoes. The signals travel down until they hit an object or the
seabed and then return to the transducer. The resultant echo appears on your
display.
The time taken for the signals to bounce off submerged objects or the
seabed, and return as echoes is measured. The data is then converted into units of
depth and can be shown in many ways such as on an LCD panel or CRT display.
The frequency of the wave or pulse, the transmitting angle of the beam, and
the power of the pulse itself, all play important parts in determining the
appearance of the echo traces on the display.
The seabed, schools of fish, seaweed, grass, bubbles, plankton, etc. all send
echoes of different strengths. Generally, the seabed sends the strongest echo, while
other objects send relatively weaker echoes.
The Fish Finder is able to distinguish fish from seaweed, grass etc. because
the air bladder of the fish is the object with the most density.
Echo Sounding
As the boat travels, echoes returning to the transducer are received which continuously update
the FF50 display.
Receiving and identifying echoes from fish can depend on several factors including:
•Species of fish
•Number and size of fish
•Fish depth below the boat
•Sensitivity level
•Power and frequency
of the sounder
•Transducer beam angle
•Boat speed
•Water turbulence
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