Sec. 47. S 



SHIP AND PROPELLER CAVITATION 



153 



0.4 0.6 0.8 1.0 \.Z 1.4 1.6 

 Advance Coefficient J 



Fig. 47.F Typical Open-Water Test Data For 



A Model Propeller, Carried into the Cavitating 



Range 



also Vol. 60, pp. 448-452], and by L. C. Burrill 

 and A. Emerson on pages 140-147 of reference 

 (7) following. 



The technical hterature contains a considerable 

 number of cavitation characteristic curves for 

 screw propellers, among which may be listed the 

 following: 



(1) Schoenherr, K. E., PNA, 1939, Vol. II, Fig. 32, p. 182 



(2) Taylor, D. W., S and P, 1943, Fig. 143, p. 116 



(3) Edstrand, H., "The Effect of the Air Content of Water 



on the Cavitation Point and Upon the Character- 

 istics of Ships' Propellers," SSPA Rep. 6, 1946 



(4) Rouse, H., EH, 1950, Fig. 63, p. 930. These are typical 



curves only, for which no hydrofoil data or test 

 conditions are given. 



(5) "Comparative Cavitation Tests of Propellers," 6th 



ICSTS, 1951, published by SNAME, 1953, Figs. 

 16-19 on pp. 78-81; Figs. 23 and 24 on pp. 85-86 



(6) Gawn, R. W. L., "Results to Date of Comparative 



Cavitation Tests of Propellers," SNAME, 1951, 

 pp. 172-213. These give the results of "interna- 

 tional" tests of selected model propellers in a number 

 of variable-pressure water tunnels. 



(7) Burrill, L. C, and Emerson, A., "Propeller Cavitation: 



Some Observations from 16 in. Propeller Tests in 



the New King's College Cavitation Tunnel," 

 NECI, 1953-1954, Vol. 70, pp. 121-150, DISS- 

 DISS; SBMEB, Apr 1954, Fig. 4, p. 284 

 (8) "Comparative Propeller Tests," 7th ICSH, SSPA 

 Rep. 34, 1955, Figs. 1-7 on pp. 170-176 and Figs. 

 11-14 on pp. 180-183. 



Although it is not yet (1955) standard practice, 

 the characteristic curves of -q, Kt , and Kq of 

 diagrams similar to that of Fig. 47.F should be 

 accompanied by drawings or sketches showing 

 the location of the cavitating regions on the 

 blades (face or back or both), the type of cavita- 

 tion encountered (bubble or sheet), and other 

 features visible in a variable-pressure water 

 tunnel, for each value of the cavitation index or 

 for each set of test conditions. This is done for 

 the 1937 ASME paper of L. P. Smith, referenced 

 in Sec. 70.40; for the discussion by F. H. Todd 

 of the V. L. Posdunine paper in INA, 1944; 

 for the SSPA Report 6 by H. Edstrand; and for 

 the L. C. Burrill and A. Emerson paper referenced 

 in the preceding paragraph. 



47.8 Photographing the Cavitation on Model 

 and Full-Scale Propellers. The visual observa- 

 tion of cavitation on screw propellers when 

 mounted by themselves in variable-pressure 

 water tunnels, initiated by C. A. Parsons in the 

 early 1900's and carried on extensively since the 

 late 1920's, has now reached the stage where 

 excellent instantaneous photographs can be taken 

 and later reproduced in the technical literature. 

 Many of these photographs are to be found in the 

 more recent cavitation references listed in Sec. 

 47.13 at the end of this chapter. 



Fortunately for the marine architect there are 

 techniques and procedures, developed in the early 

 1950's, by which still and motion-picture photo- 

 graphs may also be made of full-scale ship screw 

 propellers under operating conditions. These 

 photographs are made through a transparent 

 window in the shell near the propeller. The 

 present availability and use of powerful artificial 

 lighting dispenses with the former necessity of 

 running the vessel in the sunshine and in the 

 clear water which is usually found only in the 

 open sea. The motion pictures are stroboscopic in 

 nature so that they give the impression of a 

 particular propeller blade standing still or moving 

 slowly in the ahead or astern direction. 



To facilitate subsequent analysis and for in- 

 formation during the observing periods the screw- 

 propeller blades may be marked in advance with 

 suitable identifying letters, numerals, and signs. 



