Preliminary Evaluation of a Semi-Submerged Ship for High-Speed Operation in Rough Seas

Abstract

This paper describes the evaluation by means of model tests of an unusual hull form intended for high-speed operation in rough seas. The form can be described as a surfaced submarine, made longer and more slender in order to attain high calm-water speed. A long natural pitching period is obtained by fine, hollow waterline endings and use of large peak ballast tanks for rough-water operation. It was considered best not to attempt to keep water off the deck, and therefore comparatively low freeboard and tumblehome were adopted. Tests in regular head seas of model length and twice model length confirmed the expectation that at high speeds the semi-submerged ship could exceed the speeds at which the peaks of synchronous pitching and heaving motions occur. Consequently, in irregular head seas corresponding to a storm of Beaufort force 6, motions decreased as speed increased. Heaving was more pronounced than pitching, but accelerations were not prohibitively high even at a speed of 40 knots. It is concluded that a semi-submerged ship of the type tested shows promise of attaining much higher rough-water speeds than conventional destroyers, provided sufficient power can be installed. It is recommended that further research be directed toward providing a super-structure design that will reduce wave-impact effects and a hull form which will require less power at high speed in rough water.