Sec. 45/, 



FRICTION-RESISTANCE CALCULATIONS 



97 



ABC ship designed in Part 4, calculated by this 

 method, is given as Fig. 45.1 in Sec. 45.13. 



Values of the displacement thickness 6* (delta 

 star) are even more difficult to predict because 

 they depend upon the shape of the velocity 

 profile within the boundary layer. The ratio 

 5* = 0.145 for turbulent flow, given in Fig. 45. A, 

 is an acceptable engineering figure in the absence 

 of more definite data. 



45.6 Typical Velocity Profiles in Ship Bound- 

 ary Layers. It is regrettable that the technical 

 problems involved in the measurement of bound- 

 ary-layer profiles on ships, or even on models, 

 are of such magnitude that complete and accurate 

 observed profiles are almost nonexistent. For an 

 indication of the enormous amount of labor 

 involved in a comprehensive study of this kind 

 the reader has only to study a report by H. B. 



Freeman entitled "Measurements of Flow in the 

 Boundary Layer of a 1/40-Scale Model of the 

 U. S. Airship Akron" [NACA Rep. 430, 1932, 

 pp. 567-579]. This paper contains a considerable 

 number of boundary-layer velocity profiles of 

 the type which should be available to naval 

 architects for typical ship models. 



In the cases where ship (or model) profiles are 

 available, described in the references listed here- 

 under, either: 



(a) The velocity traverse was not fine enough, at 

 the small values of y, to follow the velocity 

 variation in the range of U (or V) less than 

 about 0.6 or 0.5 1/„ (or V), or 



(b) The velocity traverse extended only to a 

 value of y where U (or V) was approximately 

 equal to U^ (or F), despite indications that at a 

 greater transverse distance U would exceed [/„ , 



Bottom Hull PlQti nq.pf^ShJR 



Scale for Local Velocit'j U 100 



in Percentooe of Ship Speed 



Boundorvj- Lo\;er Velocitij Profiles for a Small Destrovjtr 



Zero Point 118.5 ft Abaft FP, 



"1 1 1 1 1 1 /6.10 ft below At-Rest WL 



Relative Velocitvj U • 



in PercentQoe of Ship Speed 

 -Bottom^ Hull^PlQtintf, of Ship (rnvertedj 



Fig. 45.D Typical Boundary-Latek Velocity Profiles for Several Operating Conditions on Two Ships 



