Mr« Philip Mandel, Uo So Naval Bureau of Ships, Washington, D, C, 



The author emphasizes again in this excellent status 

 report, the intimate association between the inception of 

 cavitation and the presence of nuclei of foreign material in 

 the liquids There is an old naval architect's problem that 

 has always puzzled me and I wonder now if the above is not 

 at least a partial answer to ito The problem is that of the 

 severe scale effect demonstrated many times in the past in 

 the phenomenon of rudder breakdo\m« The evidence is that 

 model rudders break down even within the speed- range of models 

 which, of course, is very low, being based on the Froude 

 Scaling LaWo On the other hand the full scale rudder, rarely, 

 if ever breaks down within the speed range of the ship. Back 

 in 19^5 in a discussion of this problem the Model Basin inti- 

 mated that this pronounced scale effect might be due to the 

 fact that the pressures do not scale properly between model 

 and full scale o Carried to its logical conclusion that 

 explanation would lead me to believe that the ship rudders 

 should break do\m. sooner than the model rudders o A somewhat 

 more plausible explanation has been offered in recent years* 

 It is claimed that the model rudder is very likely in laminar 

 flow because of its very low Reynold's Number, That flow it 

 is thought, breaks down into separation and cavitation more 

 easily than does the turbulent flow about a full scale rudder. 

 Hence the failure of breakdown to scale properlyo 



So much for previous explanations of the problem. The 

 author has mentioned the existence of cavitation within tur- 

 bulent flows and particularly within separated flows; it 

 therefore probably exists within the flow about a rudder 

 after breakdown. Since sea water must have vastly different 

 foreign material content than Model Basin water, perhaps the 

 explanation of the described scale effect lies in the different 

 liquids rather than different flows o The Author's views on 

 this line of thought would be appreciated. 



Professor M, S, Plesset, California Institute of Technology 



This paper by Mr, Eisenberg maintains the high standard of 

 his report of 1950 "On the Mechanism and Prevention of 

 Cavitation", Eisenberg "s survey of the developments in this 

 field since 1950 shows the increased effort on this aspect of 

 hydrodynamics. In spite of the increased effort, one definitely 

 has the impression that new problems are exposed at least as 

 rapidly as the old ones are solved, 



I should like to make a comment on Eisenberg 's discussion 

 of the effects of gas content and nuclei content on the incep- 

 tion of Cavitation, Ve have recently observed, at low dissolved 



