11
Fish 4430/4431 Installation and Operation Manual
Fish detection and display
The fish symbol option can be customized, or
switched off altogether so that the echoes are not
converted to fish symbols on the screen. Section
4-4 explains how to do this. The differences
between Fish symbols on and off are:
Fish symbols ON
Using NAVMAN’s SBN sonar technology
the fishfinder analyses all return signals
and eliminates most false signals and
clutter so that remaining targets are
most likely fish. Depending on the
strength of the remaining signals, they
are displayed as either small, medium
or large fish symbols with or without
depth. Whilst the SBN processing is very
sophisticated it is not foolproof and
there will be times when the unit will
not be able to differentiate between
large air bubbles, rubbish containing
air, fishing floats etc and genuine fish
returns.
Fish symbols OFF
For experienced users this will always
provide the best information as
every sonar return signal is displayed,
whether it is surface clutter, a
thermocline or a fish.
Fish Arches
In ideal conditions and with Fish symbols turned
OFF, a fish passing through the cone-shaped
ultrasonic pulse is displayed on the screen as
a fish arch:
As the fish enters the weak edge of the sonar
cone it generates a weak return signal that
turns on the first pixel on the fishfinder
screen. As the boat moves closer to the fish
the distance between the transducer and the
fish reduces and the return signal is displayed
at progressively shallower depths, producing
the start of an arch. When the fish is directly
beneath the transducer and in the middle of
the beam then the returned signal is even
stronger so the arch becomes thicker. As the
fish passes out of the cone the reverse happens
with a progressively weaker and deeper return.
In reality there are many reasons why fish
arches can’t be seen. For example:
·
Poor transducer installation - please refer to
the
Transducer Installation Guide.
·
If the boat is anchored then fish will tend
to show on the display as horizontal lines
as they swim into and out of the transducer
sonar beam. Slow speeds in deeper water
give best fish arch returns.
·
Range is important. It will be much easier
to see fish arches when using NAVMAN’s
split screen zoom mode to concentrate on
a particular section of water rather than just
displaying everything from the surface to the
bottom. Zooming increases screen resolution
and is necessary for good fish arches.
·
It is almost impossible to get fish arches
in shallow water as the transducer sonar
beam is very narrow near the surface and
fish do not stay within the beam long
enough to display an arch. Several fish in
shallow water tend to display as randomly
stacked blocks of pixels.
3-3 HISTORY screen interpretation
