408 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 61.13 



2 of Volume I. It can be made so, as explained 

 there, by substituting 3.367F„ for the Taylor 

 quotient F/VX, whereupon it becomes 



/iMin = 33.67(/0Fn 



(61. ii) 



Applying this formula to the liner of Example 

 61.V, where the draft H is 34.39 ft and the Froude 

 number F„ at the designed speed of 32 kt is 

 54.05/ V32. 174(962) = 0.307, the predicted 

 value of /iMin = 33.67(34.39) (0.307) = 355.5 ft. 

 This is compared to a limiting depth of 290 ft 

 for a ARr„ of 0.4 per cent, as derived in Sec. 

 61.11, Example 61.V. Taylor's formula is there- 

 fore conservative or perhaps on the safe side. 



61.13 Predicted Shallow-Water Resistance by 

 Inspection. The procedures described in Sees. 

 61.5 through 61.11 for determining quantitatively 



the effect of shallow water on ship speed and 

 resistance in the subcritical range are somewhat 

 tedious, and are not well suited to making the 

 on-the-spot estimates often required. Further- 

 more, they give no indication, not even approxi- 

 mate, as to what may be expected in the super- 

 critical range, which may easily be reached under 

 certain conditions in practice. 



A means of making predictions as to relative 

 speeds and resistances in shallow and deep water 

 by inspection serves a certain purpose in design 

 procedure, although it is admittedly neither 

 adequate, accurate, or reliable. The simplified 

 procedure of Sec. 61.10 and Fig. 61. J could be 

 extended to cover speed reductions from 2 per 

 cent up to 5 per cent, and possibly up to 10 per 

 cent, provided the differences between the shallow- 



Contours Are Ratios of 



Indicated Power Pi in Shallow Water 



Indicated Fbwer F] in Deep Water 



^. 



Region of 

 Greatly Augmented 

 Power 



■ 0.294- 



±=(= 



/LOO 





^'t.O 



.1.5^ ^'1.25 





1 1 ; ^^z&^ 

 III 





i.oa •'..^•695 



Reqion of IReduced Power, 

 Less ,than in Deep Water 



^^0.110 



IZS,- — " 



Line for Equal 



Pi(5hallow) 

 and Equal ^ p^^p^ 



Ji2 



Ship Speed V 



|SolitaryWave Speed Vqh" 



03 0.4 0.5 0.6 



0.3 04 05 06 07 08 09 TO Ti IZ 13 li 15 Te VT It 



Fig. 61. L One Set of Graphs for Determining Increases in Shallow-Water Total Resistance by Inspection 



