Affiliations: Experimental Towing Tank, Stevens Institute of Technology, Hoboken, New Jersey
Note: [1] Paper prerared in part under U.S. Navy Office of Naval Research and presented in occasion of the “Seventh International Towing Tank Conference”.
Note: [2] The material contained in this paper was collected as the result of the current activity of the authors in the field of the seakeeping qualities of ships, most under the sponsorship of the S-3 and H-7 panels of the Hydrodynamics Committee of the Society of Nasal Architects and Marine Engineers, and of the Office of Naval Research, Task Orders IV and V of Contract N6onr-247.
Abstract: The present paper is written as a record of an informal lecture delivered by the authors at the Office of Naval Research in Washington, D.C., on May 3, 1954. It consists of two distinct parts: the first describes the application of a theory of rigid body motions to a ship moving in a regular head or following sea; the second part deals with the problem of the representation of an irregular storm sea and of the theory of ship motions in irregular seas. The theory of ship motions in a regular sea, which is presented first, can be considered as the continuation of the work originated by Kriloff in 1896 and represented recently in the most developed form in papers by Weinblum and St. Denis. The new development consists in the introduction of coupling between heave and pitch motions, and in the more complete discussion and evaluation of various coefficients in the coupled differential equations of motions, particularly those of the cross-coupling terms. Recent experimental data obtained at E.T.T. on forcing functions due to waves show them to be much smaller than was previously assumed on the basis of the Froude-Kriloff hypothesis. A comparison of computed and experimentally determined ship motions shows quite good correlation. In the second part, some significant features of recent theories for the study of ship motions in irregular seas are discussed. It is shown that progress in this phase of seakeeping research does not need to await the complete solution of the problem of motions in simple seas.
