Sec. 61.10 



PREDICTED BEHAVIOR IN CONFINED WATERS 



403 



TABLE 61.d — Calculation of Two Spots on Deep-Water Speed-Resistance Curve from Known Shallow- 

 Water Speed-Resistance Curve 



61.10 Limiting Case of 2 Per Cent Speed 

 Reduction in Water of a Given Depth. For the 



limiting case in the first class, when the speed 

 reduction in shallow water is limited to say 2 per 

 cent of the speed V ^ in deep water, a simplified 

 procedure is justified. The points 4, and B^ 

 of Fig. 61.B are then so close together that 

 Rt^ is sensibly equal to Rtk ■ The shallow-water 

 speed Fi may be found from F„ simply by multi- 

 plying together the two ratios VJVi and V i/V^ . 

 Examination of Fig. 61.E reveals that the 

 ratio Fz/Foo is practically I.O for all values of the 

 critical-speed ratio V„/\/gh from 0.0 through 

 0.4, and that it diminishes very slowly for values 

 of that ratio through 0.7, where V,/V„ is 0.983. 



From Fig. 61. G it appears that the ratio VJVi 

 is practically 1.0 for all values of the square-draft 

 to water-depth ratio 's/ Ax/h from 0.0 through 

 about 0.12. At a y/ Ax/h ratio of 0.5 the potential- 

 flow ratio Vh/Vi has diminished only to 0.9812. 

 Each of these reductions is less than 2 per cent. 

 Combinations of values of VJVi and Vj/V^ 

 which, when multiplied together, produce a ratio 

 of V,JV^ = 0.98, representing a 2 per cent 

 reduction in speed, are plotted as the graph 

 ABODE on Fig. 61. J. These are on a base of 

 w Ax/h for the potential-flow ratio F^/F^ and 

 of V^/'vgh for the intermediate-speed ratio 

 V j/V„ . Four additional graphs, similarly con- 

 structed, cover combinations which give speed 



