What is the height of the intended mount above sea level? Figure that 1/2 the 3.9 degree angle of the beam is 1.9 (or 2, for simplicity). Look at it as a right anlge triangle and figure the
distance out ahead of you that the beam hits the surface of the water. That will be the nearest distance your radar will show on the water surface. Check your trigonomety equations. Sine = opposite divided by hypotenuse, cosine = adjacent divided by hyponteuse, and tangent = opposite divided by adjacent. The angle value you use 1.9 degrees. The right traingle is 90 degrees, 88 degrees and two degrees. You should know the height of the radar dome (mounting height). Any problem ask a high scool student who has had trig!
Isn't 48 miles a little overkill for a 20' boat?
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Plan accordingly!
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