History Screen Interpretation - NorthStar EXPLORER 443S 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 Northstar'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

3-3 HISTORY screen interpretation

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
10
Northstar Explorer 443s/443sp Installation and Operation Manual
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.
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 Northstar'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.