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" • SINGLE SCREW DESIGNS f^=-j 



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o TWIN SCREW DESIGNS /-JLr] 

 TRIAL SPEED ■ ALEXANDER, 



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TRIAL SPEED \ TROOST „ ' 



SUSTAINED SEA speed/ equation (?) 



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D "upturn" in © CURVE FOR SERIES 

 60 PARENTS FIG 18 





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 o.M 



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 0.S4 



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0.4 0.5 0.6 0.7 0.6 0.9 1.0 I.I 



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Figure 20 — Comparison of Alexander and Troost Speeds 

 with Modern American Data 



Mr. de Luce emphasised the need to relate the "upturn" speed to the speed considered 



in preparing an actual design. In Figure 21, prismatic coefficients are plotted against the 



V 

 speed-length ratio ~p^ corresponding to the speed on trial at designed draft with the machin- 



ery developing maximum rated continuous shaft horsepower, mostly taken from actual ship 

 data. The "upturn" curve reproduced from Figure 20 is again a reasonable mean through 

 the trial points, indicating that "many designers over the years have believed it desirable 

 to select dimensions and proportions leading to a flat (C) curve up to the point corresponding 

 to trial speed" (de Luce, discussion on Reference 44). 



Designs I, II, and IE in Figure 21 represented three modern (1951) designs of good 

 performance. The "upturn" speeds for these three ships are close to the mean line in 

 Figure 20, but the design speeds are higher thah the average line in Figure 21 by about 0.05 



in terms of 



VI 



Mr. de Luce stated that all three designs were being "pushed," I 



because of the economics of transporting petroleum, and II and HI for military considerations; 

 he concluded that for the purpose of evaluating hull form parameters and performance, the 

 "upturn" speed was satisfactory and independent of economic and other considerations. 

 Since 1951, when these comparisons were made, high speed has become more and more a 



V-16 



