Zigzag maneuver (10/10, 20/20)

The zigzag maneuver tests course-keeping and yaw-checking by applying helm alternately to each side. In the 10/10 test the rudder goes to 10 degrees, and when the heading has changed 10 degrees from the original course the rudder is reversed to 10 degrees the other way; the cycle repeats. The 20/20 test uses 20 degree rudder and 20 degree heading deviations. Reported results are the first and second overshoot angles and the times to check the yaw. IMO Resolution MSC.137(76) sets the overshoot limits: the 10/10 first overshoot varies with L/V and the 20/20 first overshoot must not exceed 25 degrees. It runs from a steady approach at the test speed.