Lang 



other advantages, such as : low unit cost, more flexible utilization 

 resulting from greater numbers for a given total cost, more frequent 

 scheduling, less net cost when small payloads are required, and less 

 target value in the case of military applications. 



Unusual ship designs such as hydrofoils and various types of 

 air-supported vehicles have already taken over some of the missions 

 performed earlier by monohulls. These types of craft are high per- 

 formance vehicles, and tend to be used when higher speed is impor- 

 tant, such as certain passenger craft and special military applica - 

 tions. These craft require considerable power, are more complex 

 in design, and are therefore more costly than monohulls. 



There is a need for a new type of small displacement ship 

 which has low cost, has all the desirable features of small ships, and 

 yet has many of the desirable features of large ships. 



One new type of displacement ship which has been receiving 

 considerable attention lately, especially in the oil drilling industry, 

 is called a semisubmersible. Typically, semisubmer sibles are 

 low-speed ships having two or more submerged cylindrical hulls with 

 several vertical cylinders supporting a platform well above the water. 

 These craft have been found to withstand very high sea states and 

 winds, and exhibit small motion in waves relative to monohulls. 



The term S refers to a certain class of related semisub- 

 merged ship designs and their characteristics. The S semisub- 

 merged ship concept discussed in Reference 1, and shown in Figure 1, 

 belongs to the family of semisubmer sibles ; however, it is designed 

 to provide low drag at higher speeds, and to have good seaworthiness 

 not only at rest, but underway. An S 3 tends to fill a gap in ship 

 design since it can be small, having all of the advantages of small 

 ships, and yet have the speed, deck space, and seaworthiness of 

 large ships. 



3 

 The S concept stemmed from designs of the writer dating 



back to the 1950' s. This concept was introduced at the Naval 



Undersea Center (NUC) in 1968, where it has been under active 



investigation ever since. The S 3 is not the only higher-speed se- 



misubmerged ship concept, however. Several other types have been 



designed, as discussed in Reference 1, including a single-hull 



version conceived by Lundborg dating back to 1880, a multihulled 



version described by Blair in 1929, a twin-hulled version by Creed 



in 1945, the Trisec by Leopold at Litton Systems in 1969 (Ref 2), and 



more recent versions called Modcats designed by Pien at Naval Ship 



550 



