Bindel 



2. Maioli, P.G., "Cavitazione delle Eliche nella Zona del Raccordo," Minis- 

 tero della Difesa, Comitato per i Progretti delle Navi, 5 (1966) 



3. Johnson, V.E., Barr, R^., Thiruvengadam, A., and Goodman, A., "Ship 

 Cavitation Research at Hydronautics, Inc.," Symposium on Testing Tech- 

 niques in Ship Cavitation, Trondheim, Norway, 31 May- 2 June 1967, 

 Skipmodelltanken Pub. 99, Dec. 1967 



DISCUSSION 



G. G. Cox 



Naval Ship Research and Development Center 

 Washington, D. C. 



The author's paper on the effects of shaft inclination deals with a very im- 

 portant problem for high-speed ships, whether subcavitating or supercavitating 

 propellers are used. Incidentally, the problem, although usually transient, is 

 identical to the propeller in yawed flow, as during a turn. 



Although the author has confined his investigation to the use of oscillating 

 blades in an attempt to overcome the root erosion problem, there are other im- 

 portant aspects to the problem. For instance, a normal force and yawing mo- 

 ment arise about the normal axis through the propeller disc. These are in addi- 

 tion to the usual thrust and torque along and about the shaft line. At the 9th ITTC 

 meeting, Newton [1] presented test results for a model destroyer propeller at 

 zero and 10 degrees shaft inclination. These results indicated that all forms of 

 blade cavitation inception occurred much earlier. In its turn, this cavitation 

 tended to reduce thrust and increase torque for a wide range of advance coeffi- 

 cients. This is in contradistinction to the noncavitating inclination effects which 

 tend to indicate an increase in thrust. 



Lerbs and Rader [2] presented an interesting analysis method to determine 

 the effective angle of attack for a blade section based on the concept of effective 

 aspect ratio. This method can be useful in predicting cavitation inception char- 

 acteristics for a propeller in inclined flow. 



Finally, I would like to put a question to the author. In view of the results 

 obtained from tests on one propeller with oscillating blades, does he really con- 

 sider it worthwhile to continue with the full test program indicated in his paper ? 



REFERENCES 



1. Newton, R.N., "Effect of Inclination of Shaft on Propeller Performance," 

 Trans. 9th ITTC, p. 415 (1960) 



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