Sec. 66.5 



0.40 0.50 060 0.70 030 030 



Fig. 66. a Design Lanes of Prismatic Coefficient, Displacement-Length Quotient, and Fatness Ratio 



The design lane for fatness ratios should have one or more upper branches for tugs, fishing vessels, patrol boats, and 



similar craft in the T, range of about LOO and above. However, these lanes are not well defined and are not shown here. 



The design lanes of Fig. 66. H, and those of Fig. 66.J through 66.N, embody the prismatic coefficient Cp as one of the 



principal parameters. The Cp values on the referenced graphs apply generally to the region of T, = 0.4 through T, = L20 



of the "Design Lane for Cp Values" of the present figure; in other words, to the left-hand branch only. 



fall outside these lanes when special requirements 

 are being met. For example, the fatness ratios for 

 icebreakers lie far above the upper design lane of 

 Fig. 66. A, as do those of tugs and fishing vessels. 

 This ratio, as well as the Cp , may lie above the 

 lane for any ship which has a limitation on maxi- 

 mum length or in which some important advan- 

 tage is gained by using the shortest practicable 

 length. 



Considering the ABC ship, for which there is 

 no such limitation, and consulting the upper lane 

 of Fig. 66.A with the fatness ratio 4.84 for the 

 guessed length of 500 ft, the fatness ratio is 

 found rather close to the upper limit for the T, 

 of 0.917. This 500-ft length may be, therefore, 



somewhat short for the load to be carried and 

 the speed to be made. It is well, as the next opera- 

 tion, to select a length that may be sUghtly too 

 long. This reduces the value of T, and increases 

 that of Cp . Repeating the operation for an Ldwl 

 of 525 ft, close to the values given by the Baker 

 formula, results in a T, of 20.5/ a/525 = 0.895, 

 a displacement-length quotient of 17,300/144.70 

 = 119.6, and a fatness ratio of 605,500/144,700 = 

 4.185. This spot is well inside the upper lane of 

 Fig. 66.A. 



Repeating the operation for a 515-ft length 

 gives a T, of 20.5/22.69 = 0.903, a displacement- 

 length quotient of 17,300/136.59 = 126.7, and a 

 fatness ratio of 605,500/136,590 = 4.433. This 



