Simrad NX45 Specifications download pdf (Page 42)

Simrad NX40/45 Installation and Operation Manual42

9-4 Fish detection and display

Where to nd sh

Underwater features like reefs, wrecks and rocky

outcrops attract sh. Use the 50 kHz or 50/200 kHz

frequency window to nd these features, then look for

sh by passing over the feature slowly several times

using the Zoom window. If there is a current, the sh

will often be found downstream of the feature.

A weak fuzzy band may appear between the bottom

trace and surface. This might indicate a thermocline - a

rapid change in water temperature, such as the edge of

a warm or cold current. The temperature difference can

form a barrier which the sh may not swim through. In

fresh water, sh often collect around a thermocline.

Fish arches

In good conditions, a sh passing through the cone-

shaped ultrasonic pulse is shown as a sh arch. The

50 kHz frequency uses a wider cone than the 200 kHz

frequency. This makes the sh arches easier to see.

A sh arch starts when a sh enters the weak edge of

the echosounder cone, generating a weak echo that is

shown as the start of the sh arch. As the sh moves

closer to the middle of the cone, the distance between

the transducer and the sh reduces and the echo is

shown at progressively shallower depths, producing a

rising shape. When the sh passes directly beneath the

middle of the cone, the echo becomes strongest and

thickest. As the sh passes out of the middle of the cone

the reverse happens with a progressively weaker and

deeper echo.

There are many reasons why sh arches may not be

seen. For example:

Poor transducer installation (see Transom Transducers •

Installation Guide).

If the boat is anchored then sh will tend to show •

on the window as horizontal lines as they swim

into and out of the transducer echosounder beam.

Slow speeds in deeper water give the best sh arch

returns.

Range is important. It will be much easier to see sh •

arches when using zoom mode to concentrate on a

particular section of water, rather than just showing

everything from the surface to the bottom. Zooming

increases screen resolution and is necessary for

good sh arches.

It is difcult to get sh arches in shallow water as the •

transducer echosounder beam is very narrow near

the surface and sh do not stay within the beam

long enough to show an arch. Several sh in shallow

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Simrad NX45 Specifications Page 42

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