Influence of Trim Quantity on Maneuvering Hydrodynamic Forces in Shallow Water

Abstract

This report deals with influence of trim quantity on maneuvering hydrodynamic forces in shallow water. Some captive model tests were conducted by changing trim quantity systematically. Here, a tanker type ship, which was called ESSO OSAKA, was employed. Normal force and yaw moment acting on the ship hull moving obliquely were measured at trimmed condition. Moreover, an appoximate calculation method for the hydrodynamic forces is developed on a basis of Bollay's lifting surface theory. it is assumed here that the trimmed ship can be replaced by a trapezoidal flat plate wing. And the shallow water effect is evaluated by using infinite images of the trapezoidal wing. From the results of experiments and calculation, it is pointed out that trim quantity caused by ship's bodily sinkage has a considerable effect on the hydrodynamic force in shallow water. Calculated result is also expressed by the ratio of the hydrodynamic force in trimmed codition and that in even-keel condition. As a result, it is indicated that calculated and experimental results show approximate agreement for the values of the ratio.