Yaw checking ability

Yaw-checking ability is a ship’s capacity to arrest a developing yaw rate with opposite rudder, measured by the overshoot angles in the zigzag test. After the rudder is reversed, the ship keeps swinging before the new helm checks it; the first overshoot is the extra heading beyond the switch heading after the second execute, the second overshoot after the third. IMO Resolution MSC.137(76) caps the 10/10 first overshoot at 10 degrees for L/V under 10 s, 20 degrees for L/V of 30 s or more, and (5 + 0.5 L/V) degrees between, with the 20/20 first overshoot limited to 25 degrees. Large overshoots flag a hull that is hard to stop swinging.