394 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 61.5 



be measured only in inches, the value of the 

 square draft may actually exceed the water 

 depth. Fortunately, the relationships previously 

 described continue to be reasonably valid under 

 these conditions. 



Fig. 61. D is a nomogram, designed and kindly 

 furnished by Professor H. L. Seward, by which the 

 value of the ratio -\/A^/h is determined by inspec- 

 tion when the values of Ax and h are known. This 

 nomogram is applicable to any system of units 

 provided h is expressed in a length unit and Ax 

 in the same unit squared. 



In shallow water of unlimited extent the hy- 

 draulic radius Rh equals the depth, so that 

 Rjf = h. The nomogram therefore gives values 

 of 's/'A^/Rh under these conditions. 



61.5 Features Associated with the O. Schlich- 

 ting Procedure. Several features of the Schlich- 

 ting procedure require explanation and emphasis. 

 If sufficient power is available, corresponding to 

 the shallow-water resistance at the point Gi in 

 Fig. 61. B, and is applied to drive the vessel in 



the shallow water of depth h, it will run at the 

 speed F„ . This does not mean that it overruns 

 the shallow-water Velox-system waves traveling 

 at the speed V, in the depth h but that it runs 

 in waves which are the shallow- water counter- 

 parts of a deep-water Velox-wave system traveling 

 at some faster speed V„ + AV„ . 



It is important to remember that the Schlich- 

 ting procedure involves resistances rather than 

 powers. To be sure, the effective power Pe is 

 derived directly from Rr when V is known for 

 any given condition but there is no simple method 

 of estimating the shallow-water shaft power 

 Psh when the deep-water shaft power Ps is known. 



The relationship Va,/^/~gh controls the ratio 

 Vi/Va, , of intermediate speed to deep-water ship 

 speed, independent of all reasonable absolute 

 values of Fo. , provided the intermediate speeds 

 remain well below the critical speed Cc = 'Vgh. 

 Similarly, the relationship y/Axlh controls the 

 ratio Vhiyi , of shallow-water speed to inter- 

 mediate speed, independent of the deep-water 



Fig. 61. E Graphs of Intermkdiate-Speed Ratio on a Base of Criticai^Speed Ratio 



