The subscript R defines the real part and I the imaginary part of the complex func- 

 tions. The peak value of SWATH 6A occurs near the point where the frequency becomes 

 zero. Near zero, the pitch exciting moments for both SWATH ships are almost the 

 same for both the strip theory and the slender-body theory. In this case, the major 

 factors which determine the pitch amplitudes are C , A ,., and B . The peak value 

 occurs when the pitch determinant D becomes small. Numerical values for these co- 

 efficients are presented in Table 2 where it is also shown that the value of D 

 differs by a factor of six for SWATH 6A between the strip theory and slender-body 

 theory but less than a factor of two for SWATH 6D. The peak value of SWATH 6A is 

 therefore caused by this change in the factor D. 



TABLE 2 - COMPARISON OF NUMERICAL VALUES OF PITCH DETERMINANT D FOR 

 SWATH 6A AND 6D SHIPS USING SLENDER-BODY AND STRIP THEORIES 





SWATH 6A 



SWATH 6D 



Quantities Needed 

 to Calculate D 







Slender- 



Strip 



Slender- 



Strip 



(and Units) 



Body Theory 



Theory 



Body Theory 



Theory 



L (m) 



54.3 



73.1 



2 

 M (kg-sec /m) 



0.2673.10 6 



0.2917.10 6 



C 55 (kg-m) 



0.3483.10 9 



0.9664.10 9 



gj (1/sec) 



0.0212 



0.0183 



A/L 



1.25 



0.96 



2 



I (kg-m-sec ) 



0.7825.10 8 



1.0521.10 8 



A S[ - (kg-m-sec ) 



66.11.10 9 



92.67.10 9 



573.23.10 9 



644.33.10 9 



B 55 (kg-m-sec) 



0.1599.10 9 



0.5994.10 9 



0.8222. 10 9 



1.58.6.10 9 



C 55 - (I+A 55 ) oj 2 (kg-m) 



-0.0508.10 8 



-0.0685.10 8 



-0.9537.10 8 



-1.1918.10 8 



0)B (kg-m) 



0.0246.10 8 



0.1271.10 8 



0.1504-10 8 



0.2894.10 8 



D (kg 2 -m 2 ) 



0.3186.10 14 



14 

 2.0847.10 



0.9322.10 16 



1.5041.10 16 



39 



