Lang 



(Reference 5), and for tests on a 5 -foot model of an S 3 . The drag 

 of the destroyer model increases by factors of five or more in waves, 

 while waves are shown to have no significant effect on the drag of the 

 S 3 model. 



Figure 6 shows the power required for a 3000-ton, four- 

 strut S 3 compared with the estimated power requirements for a 

 hydrofoil, a high-speed surface effect ship and a destroyer. The 

 results show that the S 3 requires significantly less power than 

 either a hydrofoil or SES at speeds up to around 50 knots. 



A photograph of a model of a 3 000 -ton S 3 is shown in 

 Figure 7, together with a list of some of its estimated characteris- 

 tics. 



STABILITY 



A wide variety of model tests have shown that the S 3 is 

 inherently both statically and dynamically stable. In regard to static 

 stability, the metacentric height in roll can be calculated from the 

 equation 



GM = — - BG 



V 



b 2 

 where I = A = moment of inertia of the total waterplane 



4 A 



area A, 



b = strut center -line spacing, 



V = displaced volume 

 BG = is the distance upward from the center of buoyancy to 

 the center of gravity. 



Large topside loads can be carried, even with a small waterplane 

 area, due to the substantial transverse and longitudinal strut spacing. 



Tests in large waves and high simulated winds have shown 

 that GM in roll should be around 3/4 of the hull diameter (alternat- 

 ively, approximately 8% of the beam), although values as little as 

 1/4 of the hull diameter are acceptable. Tests indicate that motion 

 in beam waves reduces as the roll GM increases, contrary to some 

 monohull results. However, since both wave drag and structural 

 weight increase as the strut waterplane area and spacing increase, 

 the roll GM should be made no larger than necessary. 



554 



