Motion and Resistance of a Low-Wat erp lane Catamaran 



II. 3. - Design Examples - SWATHS. 



Remarks Pertinent to SWATHS Hull Form Design. 



The design procedure previously described can easily be 

 followed in designing a SWATHS . In this case, a theoretical approach 

 is necessary since there is very little information available. Due to 

 the relatively simple geometry of a demihull, its singularity repre- 

 sentation can be much simpler in comparison with that of a usual mo- 

 nohull. A thin wall -sided strut can be approximately represented by 

 a surface singularity distribution on a vertical plane with density vary- 

 ing longitudinally but not vertically. The depth of such a distribution 

 is the same as the strut draft. In addition, vertical line source and 

 line doublet can be included to represent a strut bulb. A submerged 

 hull is represented by a line-source distribution which generates a 

 body of revolution in an infinite fluid with uniform flow. If the main 

 body is not exactly a body of revolution, it is approximated by a line- 

 source distribution which would generate a body of revolution having 

 the same sectional area curve as the main hull. 



For a surface and a line singularity distribution on a com- 

 mon vertical plane, the body generated in a uniform flow with a free 

 surface would be symmetrical with respect to the vertical plane. 

 The strut horizontal section would vary with depth, and the submer- 

 ged main hull would sag in the middle. To retain the wall sidedness 

 of the strut and to prevent the main hull from sagging, an additional 

 singularity distribution is necessary. Since the main objective of a 

 theoretical analysis is developing a hull form with good resistance 

 performance rather than achieving an accurate resistance prediction, 

 such an additional singularity has been ignored. In other words, each 

 demihull is represented by a surface singularity distribution on a 

 central plane and a longitudinal line- source distribution. 



First Design Example - A 100, 000-Ton, 30-Knot, SWATHS 



Model 5266. 



Singularity Distributions and the Theoretical Wavemaking 

 Resitance. Within the limits of constraints imposed on the hull geo- 

 metry, an optimum singularity distribution of an effective hull form 

 for both demihulls was determined. These constraints were specified 

 based on functional requirements on ship displacement and space as 

 well as ship motion. The optimization was done on the wavemaking 

 resistance first, and then the total resistance was computed. Within 



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