The best way of demonstrating how to find the set, rate and drift of a current is by using a practical example:

Problem:
From an observed position at 1200 a vessel steers 110° (T) at 12 knots. At 1330 another fix is obtained. Determine the set rate and drift of the current..

Solution:

1. Plot the 1200 position on the chart.
2. Lay off a course of 110° (T) from the 1200 position.
3. Calculate the distance steamed between 1200 and 1330.
4. Measure this distance from the 1200 position and plot the 1330 DR position.
5. Plot the actual 1330 position on the chart.
6. Join the 1330 DR position with the 1330 fix on the chart.
7. The set of the current is the direction from the DR position to the actual 1330 position.
8. The drift is the distance between the DR and the actual 1330 position.
9. The rate is the drift divided by the time interval.

A line joining the A and C positions will be the ‘course made good’ during the time interval.