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.