Download Boating Tip #16: Set & Drift (PDF format, 23KB)

Currents cause a discrepancy between your actual position and your predicted position. In addition to current, the wind, fluctuations in engine speed, your skill in steering a straight course and concentration at the helm cause you to deviate from your intended course. The longer your trip, the stronger the current, the farther off course you will be.

You can determine the course you need to steer to compensate for a known set (direction of the current) and drift (speed of the current). Plot your starting position, point A, and draw your track line. Plot the direction of the current (set) starting from point A. Using your dividers, measure a distance equal to 1 hour of current (drift) starting at point A down the set line. Mark the point where the dividers touch the set line as B. Measure a distance equal to 1 hour of boat speed with your dividers. Place one leg of your dividers on point B on the set line, and the other leg of the dividers on the track line. Mark the point on the track line as point C. Draw a line to connect points B and C, and find the course. This is the true course to steer to compensate for set and drift.

Example: Determining Course to Steer for a Known Set and Drift

Your position at 0700 is 32° 53′ N, 117° 28′ W. The current is 162° at 2 knots. Your course is 126° true and your speed is 6.3 knots. What compass course must you steer to correct for the current (set and drift) and stay on course for your destination?