The Navigation Computer: Balancing the Drift

Take the situation:

TAS = 76 knots

Desired Track = 230°

Forecast W/V = 110/40

Start in the usual way. Plot the W/V of 110/40

Put the blue centre circle onto the TAS point of 76 knots.

Now bring the desired track of 230° up to the top.

Now observe that the drift under the wind point is 20° starboard and rotate the disc 20° clockwise to bring the desired track of 230° against 20° on the DRIFT STBD scale.

Look at the wind point. The drift has increased to 25° starboard so rotate the disc 5° clockwise to bring 230° against 25° on the DRIFT STBD scale. Check the drift again. It is now 27°S.

Rotate the disc a further 2° clockwise so that track 230° is against 27° on the DRIFT STBD scale.

Check the wind point again. The drift is still 27° S. Check that 76 is still exactly under the centre dot (the blue circle).

Read off true heading 203° against the TRUE HEADING index and ground speed 87 knots from under the wind point.

Next: Wind Finding

Navigation Computer

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