Sec. ?9.17 



PROPULSION-DEVICE PERFORMANCE 



349 



torque for all angular positions and the reduction 

 of the bending moments is a design problem of 

 long standing. Nevertheless, the advent of higher 

 powers per shaft, especially on vessels carrying 

 propellers abaft skegs, and the increasing emphasis 

 on freedom from vibration, has made it necessary 

 to devote much more intensive and thorough 

 study to this project than was formerly the case. 

 A great deal of clever experimentation, carried 

 out in the period 1940-1955, has demonstrated 

 that the variable forces and moments can be 

 large enough not only to produce objectionable 

 motion of the machinery parts and generate 

 vibration in both hull and machinery but to 

 account for actual breakage of the propeller 

 shafts at sea. 



Several decades ago R. J. Walker and S. S. 

 Cook gave some data on wake and torque varia- 

 tions encountered on the single-screw tankers 

 San Florentino and Sa7i Fernando [Mar. Eng'g., 

 May 1921, p. 395]. They reported variations in 

 torque ranging from a maximum of 1.35 times 

 the mean, at a blade position of about 102 deg, 

 to 0.59 times the mean at a position, for the same 

 blade, of about 143 deg. Here the 12 o'clock 

 position is taken as deg, with angles increasing 

 in a clockwise direction, looking forward, cor- 

 responding to diagram 1 of Fig. I.E. In the plane 

 of symmetry at the disc position the wake 

 fractions were found to vary from 0.536 at 

 6 o'clock in the tip circle to 0.627 at 12 o'clock in 

 that circle. At 4:30 o'clock the wake fraction was 

 0.041; at 10:30 o'clock it was 0.255. 



Diagrams of thrust and torque variations on a 

 basis of angular position around the shaft axis, 

 for the single blades of a 3-bladed screw propeller, 

 and for the overall propeller, are given in Fig. 218 

 on page 281 of the Russian book "Korabelnye 

 Dvizhiteli (Marine Propulsion Devices)," written 

 by U. I. Soloviev and D. A. Churmack under the 

 scientific supervision of I. G. Hanovich, Moscow, 

 1948. These page and figure numbers are the 

 same in the Bureau of Ships (Navy Department) 

 Translation 408 of this book, March 1951. 



A paper by J. R. Kane and R. T. McGoldrick 

 [SNAME, 1949, pp. 193-252] was devoted to an 

 analysis of the longitudinal vibration of marine 

 propulsion-shafting systems, resulting from varia- 

 tions in the thrust forces with angular position of 

 the screw propeller. On pages 231-232 this paper 

 lists 20 references. 



More recently, N. H. Jasper and L. A. Rupp, 

 in their paper "An Experimental and Theoretical 



Investigation of Propeller Shaft Failures" 

 [SNAME, 1952, pp. 314-381], have given the 

 wake-survey diagram of a single-screw ship, 

 together with the calculated variations in pro- 

 peller thrust, propeller torque, and other factors, 

 on a base of angular position of the propeller. 

 These are supplemented by measurements of the 

 axial, torsional, and bending .strains on the proto- 

 type propeller shaft. Figs. 59. M and 59. N are 

 adapted from Figs. 33 and 34, respectively, of the 

 paper. A list of 20 references is to be found on 

 pages 364-365. 



Supplementing the foregoing, E. P. Pana- 

 gopulos and A. M. Nickerson, Jr., made further 

 full-scale tests on a larger vessel. The results of 

 this investigation were published by them in a 

 paper entitled "Propeller-Shaft Stresses under 

 Service Conditions — The S.S. Chryssi Investiga- 

 tion" [SNAME, 1954, pp. 199-241]. This paper 

 is concerned largely with the bending stresses in 

 the propeller shaft but Fig. 23 on page 227 is a 

 graph showing the variation in the calculated 

 thrust of- one blade throughout a single complete 

 revolution. The thrust varies from about 15,000 

 lb at the 9 o'clock position to 126,000 lb at 12:20 

 o'clock, to 42,000 lb at 4 o'clock, and to 123,000 

 lb at 6:36 o'clock. 



A realistic look at this situation indicates 

 definitely that an analytic procedure must be 

 developed whereby the magnitudes, directions, 

 and positions of the variable forces exerted by one 



x'=R/Rm, 



Pig. 59.M Variation of Thrust-Load Coefficient 



OF A Screw Propeller with Dimensionless Radius, 



on a Basis of Dimensionless Radius, At Four 



Angular Positions 



