611 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 70.26 



.001 0,002 0.004 



5.01 0.02 0,04 0.1 0.2 0,4 



Absolute Advance Coefficient A = 



I 1,5 Z 3 4 56 



irnD 

 Fig. 70. D Khamee's Contours of Ideal Efficiency t/a- with Jet Rotation 



Using the calculated values of Ctl = 0.730 and 

 X = 0.2738, enter Fig. 70.D, a chart prepared by 

 Kramer [see reference (31) in Sec. 70.20], and 

 determine the ideal efficiency with jet rotation tik ■ 

 This ideal efficiency tja- differs from the t// de- 

 scribed in Sec. 34.2 in that it considers the effect 

 of both the axial and rotational components of 

 the induced velocity. The better-known ideal 

 efficiency ?;/ , derived from the momentum theo- 



rem, considers only the axial component of the 

 induced velocity. 



To get a good value it is best to plot a curve of 

 riK on a basis of C'tl ■ Enter Fig. 70.D with X 

 along the bottom scale, in this case 0.2738, follow 

 the diagonal line up to the number of blades Z, 

 then move vertically to the several curves oi rj^ 

 in the vicinity of the thrust-load coefficient 

 Ctl = 0.730 previously calculated. The final 



