Install the radar | 15
• Using a protractor, measure the θ° value (for your scanner model) below the dashed line
at the bow and draw in a new line along this angle.
• Extend the new line back beyond the bow of the vessel. This is the A-B line.
3.6 How to find the theoretical maximum detection range
Propagation of the radar beam can vary, depending on the properties of the air through which it
is traveling. Under normal conditions, the distance that the radar beam travels is approximately
10% further than the distance to the optical horizon.
You can calculate the theoretical distance traveled by the radar beam using the following
formula:
D = 2.23 (√h1 + √h2)
where:
• D is distance traveled by the radar beam
• h1 is the height above sea level of the scanner
• h2 is the height above sea level of a target
An example is shown below:
In this example, the scanner is installed on the vessel at a height of 3 m (10 ft) above sea level
(h1). Island A is 10 m (33 ft) high (h2) and for comparison, island B is 5 m (16.4 ft) high (h2).
Both islands are at a distance (D) of 10 nautical miles from the vessel.
Calculations using the formula show that, at this distance, the radar can only detect objects that
are more than 7.6 m (25 ft) high, which means that island A is shown on the radar but island B
is not shown.
Remember that:
• The maximum detection range of the radar is limited by the curvature of the earth's surface
under normal conditions of wave propagation.
• Bad weather conditions can reduce the maximum detection range.
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