Experimental Investigation of Longitudinal Stability for a Submarine Ship Moving Under Free Surface

Abstract

To investigate the longitudinal stability of a submarine ship moving horizontally near the free surface, the author tried to conduct the experiments on the motion in a vertical plane and the measurements of three component forces with a tail-stabilized submarine ship model. The model is a submerged ellipsoid ellipsoid of revolution, the length of which is 1.8m and the maximum diameter 0.3m. The submergence of the model was varied from 0.15 to 0.60m. From the test data, the balance points at which the model can navigate horizontally at a constant depth were calculated. Since the tail-stabilized model must be balanced by the only one control surface under the large lift and longitudinal moment, the balance points are limited. The dynamic stability is calculated and it is found that the model is stable only in a region near the depth of 0.20m at the Froude number 0.4, due to the lacking of stabilized fin area.