11. An Analysis of the Manoeuvrability of a Ship Associated with Unusual Characteristics Under Steerage

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In this paper, the authors deal with the manoeuvrability of a ship which was reported to have shown an excessive yawing and rudder motion under automatic control. Result of spiral test has also shown that the ship responds quite capriciously at small rudder angle; i.e. the ship sometimes switched direction of turn without any change of rudder angle, and most of cases, periodical yawing of about 90 seconds was superposed. The authors, having assumed these phenomena to be induced by unsteady hydrodynamic forces caused by separation of the boundary layer, conducted experimental investigations using a free running model as well as a restrained model. Flowline observations have also been conducted on an image model in a wind tunnel. Analysing results obtained, the authors proposed a hydrodynamic explanation of this unusual behavior of the ship that it must be caused by a combination of periodic change of hydrodynamic yawing moment and an abrupt change of yawing moment on the drift angle basis.
社団法人日本船舶海洋工学会の論文