Yaw

Yaw is the rotational motion of a ship about its vertical (z) axis, the change of heading. Like sway it has no hydrostatic restoring (c_66 = 0), so its linear seakeeping equation is (I_66 + a_66) psi-double-dot + b_66 psi-dot = M_6(t), and heading is held by the rudder and autopilot rather than by buoyancy. The yaw mass moment of inertia uses a gyradius k_zz near 0.25 L. Yaw couples with sway and roll in oblique seas, and its control governs course-keeping, while loss of yaw control in stern-quartering seas is the path to broaching. In maneuvering, yaw rate r defines the turning and course-stability behavior.