Sec. 70.4 



SCREW-PROPELLER DESIGN 



587 



pp. 368-370]. Schmidt's presentation was based 

 upon the model-test data of K. Schaffran. 



The coefficients are J (= F^/nZ) by standard 

 notation) and: 



NP" 



© 



© 



PHP 



PHPw" 



PHP 



® ,3 where PHP is the propeller power 



pD'Ve 

 in horses, Ve = Va is the speed of advance in kt, 

 and D is the propeller diameter in ft. 

 There is another set of coefficients in which the 

 propeller power is replaced by the thrust power. 

 Cross curves of P/D ratio and e ( = tjo in standard 

 notation) are plotted on a logarithmic grid of J 

 and coefficient © of the preceding list. The other 

 coefficients are determined by inclined logarithmic 

 scales. 



(V) Charts of K. E. Schoenherr [PNA, 1939, Vol. 

 II, pp. 158-168]. 



The principal coefficients, all dimensionless, are: 



Thrust coefficient K, = 



prv'd* 



Torque coefficient K. = —^,i , where K, and 



pna 



K^ correspond to the standard Kt and Kq , and 

 d is the propeller diameter 



Efficiency e = ^{^ 



The values of K, ,K^ , and efficiency e are plotted 

 to a base of J. 



(VI) Charts of L. Troost and W. P. A. van 

 Lammeren [RPSS, 1948, pp. 196-223]. These 

 are based upon a so-called A-series of model 

 propellers, copied from G. S. Baker, in which 

 rather narrow blades and airfoil sections give 

 good performance but are suitable only for lightly 

 loaded propellers, outside the cavitating range; 

 and a so-called B-series, in which wider blades 

 are able to carry greater thrust loadings, the 

 losses from cavitation are small, and the propellers 

 are generally free from singing. 

 The basic coefficients are: 



ND 

 8 = -r-^ , where A^ is the rate of rotation in 



rpm, D is the propeller diameter in ft, and 

 F„ (=. Va) is the speed of advance in kt 



B„ = 'Vr2.5 , where P is the propeller power 



ses 



vl 



in English horses 



lOOOl^lP 

 A„ = — ^:rrj73 — , where Ho is the pitch in ft 



a = 



— IP 

 D ' 



•■(my 



D 



Viooo/ 



Bu = „2.6 , where U is the thrust power m 

 English horses 



V, = ^ (— V where K, is the 0-diml thrust 



coefficient, K„ the 0-diml torque coefficient, 

 A (lambda) the advance coefficient Vs/nD, and 

 rjj, the propeller efficiency. 



The contours are 8 and tj, on a grid of Ho/D 

 ratio and Bj, , A^ on a grid of the same kind, Cp 

 on the same kind, and £„ on the same kind. 

 (VII) Charts of L. Troost ["Open Water Test 

 Series with Modern Propeller Forms, Part 3, 

 Two-Bladed and Five-Bladed Propellers," NECI, 

 1950-1951, Vol. 67, Part 3, pp. 89-130]. 



This is a later system developed by Troost, 

 known as the continental or "/i(mu)-o-(sigma)" 

 system. The principal relationships are: 



H = n 



= V 



Cross curves of P/D, e{-qn), and (^(phi) are 

 plotted on a grid of ju and <r. 

 (VIII) Charts of Newport News Shipbuilding and 

 Dry Dock Company. These are described briefly 

 and one of them is illustrated in a discussion by 

 J. R. Kane [SNAME, 1951, pp. 626-627; also 

 p. 629]. 



The coefficients are J and: 



B 





'550 PHP 



pVl 



to be used when n is limited 



to be used when D is 



/ 550 PHP 



limited, where PHP is the propeller power in 

 English horses. 



Cross curves of P/D are plotted on grids of J, 

 e (= efficiency r/o), and B or A (delta). 



