Navman Fish 4430 Installation And Operation Manual page 11

The following picture shows the HISTORY
screen with the fish symbols turned off:
Strength of returned echoes
The shading indicates differences in the
strength of the returned echo from the bottom.
A black pattern indicates a strong echo, and
light grey indicates a weak echo. Fish symbols
are always shown in black.
12
Single fish
Large school
of fish
Small school
of fish
Bottom
The strength of the returned echo varies with
several factors, such as:
· The size of the fish, school of fish or other
object.
· The depth of the fish or object.
· The location of the fish or object. The
area covered by the ultrasonic beam is
approximately cone-shaped and echoes
are strongest in the middle.
· The clarity of water. Particles or air in the
water reduce the strength of the returned
echo.
· The composition or density of the object or
bottom. Mud, weed and sand bottoms tend
to weaken and scatter the sonar signal,
which results in weaker returns. Rock or
coral bottoms concentrate the return signal
for strong returns.
Note: That 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.
Large fish
Kelp / weed
Hard bottoms such
as rock or coral show
as wide bands at the
bottom of the screen
Soft bottoms such as
mud, weed and sand
show as narrow bands at
the bottom of the screen
Fish 4430/4431 Installation and Operation Manual