G„ = y [-H (K X ) - Y (K x ) + 2i J (K x ) ] 

 3 4 o o o 



(124) 



where H is the Strove function, and J and Y are Bessel functions of the first and 

 o o o 



second kind. 



RESULTS AND DISCUSSION 

 To test the numerical results, we have selected three models of SWATH ships: 

 SWATH 6A, SWATH 6C, and SWATH 6D. Experimental tests for motion have been carried 

 out for all three models. All models have the same lower hulls and the same distance 

 between the two hulls, but differ in the shape of their struts. SWATH 6A has a 

 single strut on each side while SWATH ships 6C and 6D have twin struts. The thick- 

 ness of the struts differs for all three models. The principal dimensions of these 

 models are given in Table 2. Because our primary interest is the motion at low fre- 

 quencies of encounter, the computations have been carried out when the forward speed 

 is 20 knots. 



TABLE 2 - PRINCIPAL DIMENSIONS OF SWATH SHIPS* 



Dimension 



SWATH 6A 



SWATH 6C 



SWATH 6D 



Displacement, long tons 



2579 



2602 



2815 



Length at waterline, m 



52.5 



60.2 



68.0 



Length of main hull, m 



73.2 



73.2 



73.2 



Beam of each hull at waterline, m 



2.2 



2.6 



2.2 



Hull spacing between centerline, m 



22.9 



22.9 



22.9 



Draft at midship, m 



8.1 



8.1 



8.1 



Maximum diameter of main hull, m 



4.6 



4.6 



4.6 



Longitudinal center of gravity 

 aft of main hull nose, m 



35.5 



34.7 



36.1 



Vertical center of gravity, m 



10.4 



10.4 



9.1 



Longitudinal GM, m 



6.1 



13.7 



26.4 



Radius of gyration for pitch, m 



16.9 



17.7 



19.0 



2 

 Waterplane area, m 



193.9 



181.4 



253.9 



Length of strut, m 



52.4 



25.8 (per 

 strut) 



25.8 (per 

 strut) 



Strut gap, m 



" 



8.6 



16.4 



Maximum strut thickness, m 



2.2 



2.6 



3.1 



^Dimensions are full-scale. 



35 



