Seakeeping Characteristics of Small-Waterplane-Area-Twin-Hull Ships

Abstract

In this paper, an up-to-date evaluation of the Seakeeping characteristics of small-waterplanearea-twin-hull (SWATH) ships is made. A brief review is given of the most recent experimental data and theoretical results applicable to the prediction of the seaworthiness characteristics of SWATH ships. Using these data and results, the Seakeeping characteristics of SWATH ships are compared with the characteristics of conventional monohulls and conventional catamarans. It is shown that the SWATH configuration has some very promising seakeeping characteristics. For example, a 220-ft SWATH ship in a sea state 5 at normal operating speeds and without any foil or control surfaces will have practically no pitch, heave, or roll motions in head, bow, and beam seas. In very severe headseas and particularly in long swells, this study indicates that SWATH ships without foils or control surfaces will exhibit motions of considerable magnitude. At zero forward speed in head seas, the vertical motions of SWATH ships will be of approximately the same magnitude as those for a monohull with equivalent length. On the other hand, in quartering and following seas, a SWATH ship will pitch more than a conventional monohull with equivalent displacement if not equipped with foils or control surfaces. There is also some indication that in beam seas, a SWATH ship will experience larger sway motions than conventional hull forms.