Hec. 56.10 



OBSERVED SHIP-RESISTANCE DATA 



309 



i^kl 



4 5 6 7 8 S 10 



Fig. 56. M Plot of /?r/A on T, for Many Vessels at Their Designed Speeds 



vessels of many types. The data indicated by the 

 small circles on the figure are derived from cal- 

 culated values of the total resistance of the ship, 

 based upon model tests, at the speed listed in the 

 general-information block on the respective 

 SNAME RD sheets. Unfortunately, the model 

 data on some sheets are for bare hull only; on 

 other sheets they are for the hull plus simple 

 appendages. This variation is considered not too 

 important as the plot is intended for indicating 

 approximate values only. 



It is found that a single tentative meanline 

 passes close to or through most of the designed- 

 speed spots, regardless of the size or type of 

 vessel or of the T, at which it runs. For the higher 

 Tj values there is considerable dispersion in the 

 few available spots, especially as the vertical 

 scale is logarithmic and the variations in per cent 



are considerably larger than the apparent varia- 

 tions on the figure. It is possible that a single 

 meanline will not suffice in this region, especially 

 in view of the large variations in characteristics 

 of vessels running at the same T, value. For 

 instance, the upper circle at a T, of about 1.93 

 represents a small patrol boat with a displacement- 

 length quotient of 93.4, while the lower circle at 

 a r, of about 1.985 represents the destroyer 

 Hamilton, with a displacement-length quotient 

 of only 40. The plot of Fig. 56.M does, however, 

 indicate regions of T^ where the data for certain 

 classes of vessels are to be found. 



It is probable that, as more model data are 

 plotted in the upper right-hand corner of this 

 graph, the final meanline will be considerably 

 lower than the one now indicated, especially for 

 high-speed craft of good to e.xcellent performance. 



