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[goldorak]

For those wishing to implement Ekelund ranging on a scientific programmable calculator here is the formula :

The input fields are 8 (4 for the first leg and 4 for the second leg)

• OwnSpeed_1
• OwnCourse_1
• TrgBearing_1
• BearingRate_1
• ---
• OwnSpeed_2
• OwnCourse_2
• TrgBearing_2
• Bearing Rate_2
  

For leg 1 :

OOA_1 :

Calculate X = TrgBearing_1 - OwnCourse_1
If X > 180 then 360 - X
If X < 0 then X + 360
Else X

Once calculated OOA_1, calculate sin (OOA_1)*OwnSpeed_1

The calculation for OOA_2 is the same as OOA_1 mutatis mutandis.

Ekelund Range = 0.955 * [ |sin(OOA_1)*Ownspeed_1 - sin(OOA_2)*OwnSpeed_2| ] / [ |BearingRate_2 - BearingRate_1| ].

Speeds expressed in knots, bearing rate in degrees/min and distance is yards.
Numerator and denominator in the formula have to be positive so absolute values are used.