Manually calculate a calibration factor

New calibration factors can be calculated manually following the steps below.

Prerequisites:

  • You will need to be underway, with sufficient space to maneuver unhindered.

  • To ensure accuracy, water conditions should be calm with zero tide and zero current.

  • You will need to calibrate each calibration speed point, starting with the lowest

CalibrationSpeedManual calibration factorsSpeed calibration

  1. Run your vessel at a steady speed, approximately that of the selected calibration speed, over a measured distance making a note of:.

    • The measured distance in nautical miles

    • The current speed value in knots

    • The time in minutes it takes to cover the measured distance

  2. Calculate the actual speed over the measured distance using the calculation: (Speed = (60 x Distance) / Time) ‘60’ is used to ensure the calculation is in minutes rather than hours or tenths of an hour.

    e.g. Distance (D) = 14 nautical miles, Time (T) = 105 minutes (1 hour 45 minutes) so:

    • S = (60 x D) / T

    • S = (60 x 14) / 105

    • S = 840 / 105

    • S = 8 kts

If the calculated speed is:

  • The same as the current speed, (noted during the Speed Run Calibration) then the calibration is correct at this speed so no action is required.

  • Not the same as the current speed. Calculate a new, corrected calibration factor, as follows:

    E.g. if actual speed equals 8 kts, indicated speed was 7.5 kts and the old calibration factor was 1.4 then:

    • New cal factor = actual speed x old factor / indicated speed

    • New cal factor = 8 x 1.4 / 7.5

    • New cal factor = 11.2 / 7.5

    • New cal factor = 1.49