At a depth of 15 m this shape had an inception speed of 18.5 m/s. The cavitation calculations 

 were based on the computed, potential flow, pressure distributions for smooth forebodies. 

 Rough forebodies would have lower inception speeds. The pressure distributions on the 

 models of the first series are given in Figure 4 and of the second series in Figure 5. Minimum 

 values of the pressure distributions are listed in Table 2. 



CONSTRUCTION 



The models were constructed of molded Fiberglas and consisted of three sections. The 

 second and third sections were common to all models and consisted of part of the parallel 

 middle body and the afterbody, respectively. The first section included the forebody and the 

 remainder of the parallel middle body. For each of the first sections, the length of the 

 included parallel middle body was adjusted to insure constant volume for all models. The 

 third section was obtained from an existing model of the research submarine ALBACORE 

 (AGSS-569) by cutting the model in two parts at the position of maximum diameter. 



Special care was taken in the construction of the forebodies of the models. Profile 

 tolerances were held to ± 0.4 mm; all imperfections were removed and meridians were fared. 

 The Fiberglas was polished to a 0.64-micron, root-mean-square, surface finish. This insured 

 roughness Reynolds numbers two orders of magnitude lower than the number considered 

 necessary to trip turbulence prematurely. 



EXPERIMENTS 



GENERAL 



The model drag experiments were conducted in the David W. Taylor Model Basin, using 

 Carriage 2. This towing basin is 846 m long, 15.5 m wide, and 6.7 m deep. Drag and speed 

 data were collected for each model in the speed range between 0.51 and 5.15 m/s at intervals 

 of approximately 1 /4 m/s. A waiting time of 5 min between runs was selected because no 

 effects of residual turbulence from preceding runs could be detected after this time. Flush- 

 mounted hot films were inserted in the model surface at selected locations to determine ths 

 extent of laminar and transitional flow and the location of laminar separation when it 

 occurred. Water temperatures were monitored throughout the test period to obtain water 

 densities and kinematic viscosities. 



