(in Russian, tsirkuliatsiia sudna), the path of the center of gravity of a ship when the ship’s rudder is turned through some angle and held in that position. The Russian term tsirkuliatsiia sudna is also frequently applied to the process of turning a ship.

The turning of a ship consists of a maneuvering phase, an evolutionary phase, and a steady-state phase. The maneuvering

Figure 1. The turning path of a ship and the main parameters of the ship’s turning circle

phase coincides with the time interval during which the rudder is swung. The evolutionary phase lasts from the moment the rudder is held at a constant angle to the moment the elements of the ship’s motion cease changing with time. During the first two phases, the path of the ship’s center of gravity is a line of varying curvature; during the steady-state phase, the path is a circle (Figure 1).

The elements of a turning circle are the steady-turning diameter D, the tactical diameter D_T, the advance l₁, the transfer l₂, and the offset l₃. The determination of these elements is an important step in the evaluation of a ship’s maneuverability. The course of a ship cannot be plotted, especially during maneuvers, if the elements of the turning circle are not known. An element of a turning circle is determined by computation and is checked during sea trials.