Johnson, Jr. 



h = elevation of the nozzle 



u 



T = total thrust at design speed 

 T„ = basic thrust at design speed 



A. = inlet area 



1 



c„ = resistance coefficient 



Q = flow rate 



B = constant for the weight of the pump 



R = range 



F = specific fuel consumption 



L = duct length 



a,„ = correlation factor 



A = weight of the pump 



p 



A, = weight of propulsion device (wet) and its installation 



e = any parameter able to express resistance per unit displacement 

 weight, as D/A or D/L 



A = weight at disposal for optimization 



n 



A' = A + A 

 n n u 



As you can see, two cases are considered above: the free jet, that is, the jet 

 the inlet of which does not lie in the boundary layer, and the jet on wake, that is, 

 the jet the inlet of which does lie in the boundary layer. 



The effect of mounting the propulsion device on board is expressed by the 

 term T-Tb , which may be divided into three parts, the first of which considers 

 the effect of weight increase, the second the effect of additional elements in the 

 water, and the third the effect borne on resistance by a particular weight, that 

 is, the pump. 



For the subsequent elaboration of the basic formulas we have considered 

 the weight of the pump as a linear function of the flow rate. This, of course, is 

 not really the case, as the weight of the pump depends on several different ele- 

 ments, as it is well known. But if we calculate the value of the constant B , hav- 

 ing in mind a particular type of pump the flow rate of which lies at some point 

 between 70% and 140% of the flow rate of the actual design, the above -said as- 

 sumption may hold good with sufficient accuracy. 



1056 



