Simrad NX40 Installation Manual download pdf (Page 16)

14 | Install the radar

3.4 Yacht installations

Normally you should install the scanner horizontally, to produce an equal sweep around the

yacht. However, a yacht heels over to the lee side, and when the heel angle exceeds 50% of

the vertical beam width of the radar, this can cause two problems:

• On the windward side of the yacht, the beam is projected too high to sweep the water

surface effectively. Targets can be missed completely or appear at very poor resolution on

the display unit.

• On the lee side of the yacht, the beam is projected too low and is concentrated over a small

area of water so that sea clutter becomes a problem on the display unit.

In this case, you're recommended to install the scanner on a gimbal mounting so that it can

operate effectively in a heavy swell or when the yacht is heeled over.

3.5 How to find the optimum height for the scanner

The optimum height for the scanner is as close as possible to the A-B line for best performance.

How to find the A-B Line:

The vertical extent of the radar beam is 2θ°, so most of the radar beam is concentrated within

this angle, meaning that outside of this angle, the radar beam will be very weak.

Scanner model θ° value (half the -3 dB beam width)

6 kW 10

10 kW 10

25 kW 10

An example of an A-B Line is shown in the picture. If you install the scanner below the A-B line,

the scanner will be too low. It will be difficult to acquire distant targets and the superstructure

will be more likely to impede the passage of the beam and generate false echoes.

If the scanner is installed too high above the A-B line, the beam will miss close targets and

increase sea clutter return.

You can find the A-B line for any vessel as follows:

• Using a scaled drawing of the vessel, lay a rule along the line of the main deck and

continue this forwards as a dashed line extending beyond the bow.

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Simrad NX40 Installation Manual Page 16