Hydrodynamia Design of an S 3 Semi submerged Ship 



of hull diameter to tank depth was l/l6. Dr. Chapman's analysis of 

 drag indicates that the model drag would increase at most a few per- 

 cent, depending on speed ; corrections for tank size have been made 

 in the model tests. There is no evidence that tank depth has an effect 

 on motion. One reason why tests were conducted in the larger model 

 basin at Escondido, California, and in San Diego Bay was to verify 

 that there were no significant effects of tank size on performance. 

 The results on the 1 1 -foot model at NSRDC showed essentially equi- 

 valent results. Thus to date, we have seen no significant effect of 

 tank size on the model characteristics 



DISCUSSION 



Christopher Hook 



Hydrofin 

 Bosham, Sussex s U. K. 



This extremely interesting paper by Dr. Lang I must disagree 

 with on the matter of his comparisons as given in Figure 6. If we 

 refer to Figure 14 of the Silverleaf 42 n< ^ Thomas Gray Lecture 

 (paper) given to the Institution of Mechanical Engineers and entitled 

 "Developments in High Speed Marine Craft" we see that whereas the 

 SES or amphibious Hovercraft shows higher speeds and better rj (L/D) 

 values in calm water than the Hydrofoil, this situation is reversed in 

 even moderate sea conditions and we get : Hovercraft rj (L/D) = 

 2 to 3 against submerged Hydrofoils approximately 6, and surface 

 piercing hydrofoils 3 to 6 . 



Now since the whole point of the raised platform is to elimi- 

 nate wave effects as much as possible, it follows that it is unfair to 

 present SES curves based on performances restricted to calm water 

 and progressing right off the graph to the right, i. e. to a speed range 

 which is far from having ever been demonstrated. I am informed on 

 the best authority that until new skirt techniques have been developed, 

 100 knot speeds remain out of the question. 



To be specific, in Figure 6 Dr. Lang appears to claim some 

 10 knot more speed for a given power than for a hydrofoil but that is 

 not what he claimed verbally in this presentation. Surely there is a 

 mistake here. 



579 



