The SWATH ship is a displacement hull form that departs from monohull ships and catamarans yet draws on the technology and design experience of traditional naval architecture. The SWATH concept replaces the conventional underwater hull shape with two demihulls consisting of submerged submarinelike bodies connected to the above water platform by streamlined surface-piercing struts. The low waterplace area that results reduces the motions caused by wave-induced forces just as in the case of off-shore drill rigs. The wide spacing of the demihulls provides a high degree of maneuvering control.

The SWATH concept has been under investigation by the U.S. Navy for over 10 years. This paper summarizes the technology developed in the areas of seakeeping, maneuvering and control. The development of the concept is traced through numerous model experiments. Experience with the 220-ton workboat SSP KAIMALINO is emphasized. Designer controlled parameters, such as waterplane area, natural periods, number of struts, metacentric height, and strut shape are discussed. The effect of parameters on performance is evaluated by computer prediction programs. Lessons learned from past designs and considerations for the future are identified. The results present a picture of the state-of-the-art technology as it developed from 1969 to 1979 and establish the potential of this new type of ship for naval and off-shore applications.


The SWATH ship is a displacement type hull from that departs significantly from conventional ships yet draws on the technology and design experience of traditional naval architecture. It offers high performance by providing the platform steadiness and sustained speed capability in waves of a conventional ship three times as large.

An Englishman by the name of Creed first brought the SWATH concept to the attention of the U.S. Navy in 1943, as a superior platform for aircraft operations. The current Naval program began in the late 60's when Lang1 designed the 190-ton SSP KAlMALINO as a workboat for the Naval Ocean Systems Center (NOSC) in Hawaii. The SSP has been used to demonstrate the SWATH concept and to validate some of the technology. Participation of David W. Taylor Naval Ship Research and Development Center (DTNSRDC) in the development of SWATH Ship Technology began in 1969 as part of a study of candidate configurations for 25,000 ton aviation ships.

During the decade from 1969 to 1979 the technology advanced rapidly. This paper describes the status of the dynamics effort which is a key to developing an understanding of SWATH ship design. Current technology will be shown to be adequate for the logical next step of building a SWATH ship large enough to undergo Fleet evaluation.

The acronym SWATH (Small Waterplane Area Twin Hull) was selected by the Navy in 1972 to reduce confusion between this concept and another type of twin hull ship -- the conventional catamaran, which is different in many important respects. Physically, the most apparent differences between the two concepts are below waterline.

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