Model 



Sand Strips 



Trip Wire 



Studs 



4200 (0.60 Cg) 



Slight increase over lower 

 speeds 



No change 



- 



4201 (0.65 Cg) 



No change except at very 

 lowest speed, C j rising 

 slightly with decreasing 

 speed 



No change except at 

 very lowest speed, 

 C -J- level with de- 

 creasing speed 





4202 (0.70 Cg) 



No change 



- 



No change 



4203 (0.75 Cg) 



Below-L- ^04 



large increase in resis- 

 tance—some 60 percent 

 on C^ . At service speed, 

 increase in C^ was 4 per- 

 cent and in Cj- about 1 V2 

 percent 





Same as sand strips 



4204 (0.80 Cg) 



Slight increase at all 

 speeds-Cj. up 1 Yn per- 

 cent at service speed 



— 



Somewhat larger in- 

 croase-Cy- up 3 per- 

 cent at service speed 



(The percentage increases are for a 400-ft ship) 



In view of the small effects of stimulation, it was decided to use results with sand 

 strips without deduction for any parasitic drag. 



The first step in developing the new Series 60 was a comparison between the results 

 of certain good ships and the Series 57 equivalents. Studs were used for these tests because »i 

 they were easy to fit, were positive in location, had some theoretical backing as a means of 

 stimulation, and had very small parasitic drag. The only peculiar results found were with the 

 models of the PENNSYLVANIA series. The- PENNSYLVANIA was a tanker of 0.76 Cg and 

 a number of variations were tested. The models are listed in the order in which the tests were 

 carried out. For the first five, the increases in resistance were quite substantial, averaging 

 10 and 7.5 percent at the service and trial speeds respectively. For the last four, the cor- 

 responding figures were 0.8 and 1.2 percent. It should be noted that Models 4435W and 

 4435W.A are built to identical lines, both of wax, and yet they fall into the two groups as 

 regards stimulation effects. The ©400 ft values listed are those derived from the model 

 results with stimulation; they show no serious change in the resistance picture, indicating I 

 that the differences occurred in the tests in the unstimulated conditions. The only division j 

 one can make is a chronological one, and no explanation has been found for this peculiar 

 behaviour. 



A-2 



