382 



HVnRODYNAMICS IN .SHIP DESIGN 

 TABLE 60.C— (Continued) 



Sec. 60.13 



Should the basic data be given in metric units, 

 Eq. (34.xxv) is replaced by 



^ [ 1,000(0.5148)' "] 

 L 75(9.806) J 



■[ 



M = 



(W in metric tons)(y in kt)' 1 

 (L in meters)(Ps in metric horses) J 



whence M = 0.1855 times the second term. 



It is emphasized that variations of the merit 

 factor equations such as those listed produce 

 exactly the same numerical values for consistent 

 units in any sj'stem of measurement. 



At an early stage in a preliminary design the 

 displacement weight W and the speed V are 

 generally known within rather close limits. There 

 is either a hmiting length L or a range of probable 



lengths from which the speed-length quotient 

 T", or the Froude number F„ is derived. Taking a 

 selected or average merit factor M from Fig. 

 34.1 for the value of Fl at the designed speed, 

 the estimated shaft power Ps is rapidly calculated 

 from the equation 



= r0.6lir (IF in tons)(F in kt)' "] 

 ~ L M JL L in ft J 



(60.i.\) 



This is done for the preliminary design of the 

 ABC ship in Sec. 66.9, using a Telfer merit factor 

 M of 9.5 and an Fl of 0.0727. From the model 

 tests made subsequently on the transom-stern 

 ABC design, using the data reported in Sec. 

 78.16 for a ship speed corresponding to 20.5 kt, 

 the Telfer merit factor M works out as 



