and 



C = 



ehp X 427.1 



A2/3 • F3 



where V is the speed of ship in knots 



A is the displacement of ship in tons salt water, (2240 lb), and 

 ehp is the towrope horsepower for the ship. 



The values of ehp used in calculating (C) have been deduced from the model experi- 

 ments by the use of the ATTC 1947 friction formulation and include the ship correlation 

 allowance of +0.0004. Therefore both the C j- and (?) values are based on the same data 

 and are directly comparable in this respect. 



', and (K) are related linearly for any one model. A corresponding 



set of values is given below, from which any other conversion can be made: 



TABLE 8 



V ,^ 



Relation between Cg, , and (^ 



Model 

 Number 



Cb 



V 



V 



® 



^^BP 



^hl 



4210W 



0.60 



0.96 



0.952 



2.515 



4211W 



0.65 



0.86 



0.853 



2.198 



42I2W 



0.70 



0.76 



0.754 



1.895 



4213W 



0.75 



0.66 



0.655 



1.609 



4214WB-4 



0.80 



0.56 



0.556 



1.334 



A vast accumulation of model resistance data based on the Froude skin-friction 

 coefficients is available in the transactions of societies and reports of model basins. Since 

 1948 this method of extrapolation from model to ship and that based on the ATTC 1947 

 (Schoenherr) line have both been recognized by the ITTC as acceptable for use in all pub- 

 lished data. A quick graphical method of mutually converting the (?) values based on 

 these two formulations was published by Gertler in 1948.''^* The ATTC values used therein 

 include the allowance of + 0.0004 for ship correlation allowance, so that the application of 

 this chart to the ATTC (?) values given in this present report will yield directly the 

 equivalent (?) values based on the Froude coefficients. 



*The chart in this report is reproduced as Figure D-4 in Appendix D. 



V-13 



