Sec. 60.7 



SHIP-POWERING DATA 



',67 



ABC Ship 

 Transom -Stern Desiqn 

 TMB Model 4505 

 EMB Model Propeller 2294 

 Data Token from Wake 

 JDiQ<^rQm at Propeller Position 



Plot of Averaoe Wake Fraction w on Radius 



0.1 



0.2 03 0.4 as 0.6 0.7 0.8 03 1.0 

 R/RMqx 



O.SO I? 



0.15 i 



0.10 a 



'0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 

 Anc^ular Position, deo, Measured Clockwise From Top Center; see Diaqrom 



Fig. 60.N Wake-Analysis Diagram for Transom-Stern ABC Ship, 

 Applying to Fig. 60. M 



the radial variations for each position are aver- 



Fig. 60.M is a plot of the 3-diml wake survey 

 for the transom-stern ABC ship of Part 4, made 

 at the designed speed. Fig. 60. N is a graphic 

 analysis of these data, prepared as a preliminary 

 step to the design of a wake-adapted propeller for 

 this vessel, described in Chap. 70. Values of wake 

 fraction w are plotted in Fig. 60.N for three 

 0-diml radii, corresponding to x' = R/Run^ of 

 1.00, 0.727, and 0.453, on a basis of angular 

 position around the shaft axis. Averages for the 

 complete revolution give 



R 



Rt. 



of 1.00 



0.727 

 0.453 



w = 0.1923 



0.1693 

 0.1568 



A plot of radial variation for wake fractions, when 

 averaged around the entire circumference at each 

 0-diml radius, is given in the upper right-hand 

 corner of the figure. 



A somewhat more comprehensive method of 

 analysis, probably representing more nearly the 



development of the future, is given by N. J. 

 Brazell [SNAME, 1947, pp. 146-149], but the 

 present author does not intend that these remarks 

 shall be construed as an endorsement of all the 

 detail steps and the calculation methods employed 

 in that reference. 



Finally, the model or ship propeller acts as an 

 averaging or integrating instrument by taking 

 account, degree by degree around a revolution, 

 of the multitudinous variations in magnitude and 

 direction of the incident-velocity vectors for the 

 complete range of radius from hub to tip. How- 

 ever, because of the variations in direction as 

 well as magnitude, involving changes in effective 

 angle of attack, thrust, torque, blade loading, and 

 the like, no direct analytic procedure has been 

 devised for averaging actual wake velocities at a 

 screw-propeller position. 



By finding the speed of advance Vo at which 

 the same propeller, when tested in open water, 

 produces the same torque (or thrust) as when run 

 behind the model or ship, one assumes that the 

 average speed of advance V^ "behind" is the 

 same as the speed Vo in the "open." Then knowing 

 the speed V of the model or ship, the wake 



