Sec. 593 



PROPULSION-DEVICE PERFORMANCE 



333 



quate and precise definition for the information 

 presented. Only rarely are the particular forms 

 of propulsion device, corresponding to the 

 efficiency curves, diagrammed or illustrated. The 

 graphs or accompanying text do not always state 

 whether the efficiencies are maxima, averages, or 

 service values. 



A rather large array of tabulated data derived 

 from the self-propulsion tests of shallow-draft 

 vessels with tunnel sterns is published by A. R. 

 Mitchell [lESS, 1952-1953, Vol. 96, pp. 125-188]. 

 These data do not, unfortunately, include values 

 of the screw-propeller efficiencies but they do 

 embody information on wake and thrust-deduc- 

 tion fractions and on propulsive coefficients. 



H. Mueller has presented, for screw propellers 

 of four different P/D ratios and for three varia- 

 tions of the current (1955) rotating-blade pro- 

 peller, two sets of graphs showing variations with 



oo 100 20 10 5 4 3 2 I 0.8 O.G 0.4 



Thrust-Load Factor Cjl 



Fig. 59. a Values of Real Propeller Efficiency of 

 Typical Screw Propellers for a Range of Pitch- 

 Diameter Ratio and Thrust-Load Coefficient 



^°-- 



oo 100 20 10 E 4 3 2 1 .9 .8 .7 .S 0.5 0.4 



Thrust-Load Factor Cj^ 



Fig. 59.B Values of Real Efficiency for a Screw 

 Propeller and Several Rotating-Blade Propellers 



thrust-load coefficient of what he calls "the degree 

 of perfection" of these propellers [SNAME, 1955, 

 pp. 4-30]. This is the ratio of the (open- water) 

 propeller efficiency to the ideal efficiency, cor- 

 responding to what is defined in Sec. 34.4 of 

 Volume I as the real efficiency, symbolized in the 

 form TjReai = fiaHi ■ Figs. 59. A and 59. B, em- 

 bodying these graphs, are adapted from Mueller's 

 Figs. 6 and 7, respectively, of the reference cited. 



59.3 Open- Water Test Data for Model Screw 

 Propellers. For every model propeller charac- 

 terized by the model-testing establishments of the 

 world, involving models numbered in the thou- 

 sands, the test results are available (in their 

 archives) for a wide range of real-slip ratio s^ or 

 advance coefficient J . As for making these data 

 available to the profession at large, the charac- 

 teristic curves plotted from the open-water 

 observations on more-or-less unrelated propellers 

 have been published in sporadic fashion, embody- 

 ing probably not more than one per cent of the 

 grand total. The availability of test data for 

 related or series screw-propeller models is dis- 

 cussed in the section following. 



The search for, and the systematic listing of 

 the published source material for open-water test 

 data on unrelated models is a formidable task. 

 Much more of a task is the collection and pre- 

 sentation of these data in usable form, corre- 

 sponding to the SNAME Propeller Data sheets. 

 One set of these sheets, made up for TMB model 

 propeller 2294, is reproduced in Figs. 78. Ma, 

 78.Mb, and 78.Mc of Part 4. The open-water 

 characteristic curves for an 18-inch diameter 

 TMB model propeller, tested as part of the ITTC 

 program on comparative cavitation tests, are 

 presented in Fig. 59. C. The arrangement of graphs 

 in this figure is slightly different from the normal, 

 represented by the diagram of Fig. 78.Mc, 

 principally to keep the Kt and Kq curves clear 

 of each other. 



A portion of the information relative to open- 

 water test data which has come to the attention 

 of the author in the preparation of the present 

 volume is listed hereunder: 



(1) Schmierschalski, H., "Ergebnisse sj'stematischer 



Modellversuohe mit hochtourigen flachgangigen 

 Schraubenpropellern (Systematic Results of Model 

 Tests with High-RPM, Low-Pitch Screw Pro- 

 pellers)," WRH, 7 Aug 1930, pp. 329-335. Log- 

 arithmic propeller charts, for area ratios of 0.42, 

 0.56, and 0.70, are given on pp. 333-335. 



(2) TMB model propellers 1186-1187, 1188-1189, and 



1190-1191; 3-bladed, built-up type, with modified 



