How it works: Yacht Radar

Author of Illustrated Navigation Ivar Dedekam who has extensive sailing experience over 30-plus years explains how yacht radar works

To utilise radar properly it’s imperative that you learn how to interpret the information displayed. Many objects produce such a poor echo they don’t show up on the screen. Fixed and floating markers and buoys usually show up quite well but shadows and indistinguishable echoes can be a problem.

Remember as well that the coastline and configurations of islands may appear totally different compared to the chart. Blind spots due to mast and superstructure can also pose a problem. False echoes can often occur in conjunction with blind spots, while interference from other radars can disturb the display as well.

Therefore, take every opportunity to practise interpreting what you see on your radar display. You should do this in daylight and clear weather by comparing what you see on the display with what your own eyes are actually seeing, whilst referring it all to the chart.

Antenna

Theoretically the antenna should be mounted as high as possible. But if it’s mounted too high, pitching and heeling will reduce the radar’s ‘vision’. On leisure craft 4m is considered to be a good height. The antenna should also have unobscured sight as masts and superstructure can produce a ‘shadow’ or ‘false’ echo.

Gain

It’s important to adjust ‘gain’ correctly. Gain is the amplification of the received echoes. If the gain is too low, echoes from small objects may be omitted. If it’s too high, the screen will show lots of small dots which could obscure the small echoes. The best setting is when these dots are barely visible.

Sea clutter

Because of the antenna’s large vertical beam width (usually 25-30°) it’s possible that waves close to the boat will reflect the radar’s signals, especially if the boat is rolling or pitching. Use the sea clutter adjustment with care as too much damping can erase echoes from dangerous objects.

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Tuning

Tuning is crucial to the quality of the reception of echoes from surrounding objects.
As a rule you will have correct tuning when the picture is at its sharpest. Some radars have indicators to assist tuning. Tuning should be carried out every time you change range.

Range

A radar’s range depends more on line of sight than wattage. Small craft radars have a transmitting power of 1 to 2kW, which usually means a range of about 16 to 24 miles. Larger radars transmitting at 4kW have a range of up to 36 miles.

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