of small size offer attractive possibilities at high speed 

 together with the ability to ride over relatively severe waves o 

 Here again cavitation is one of the limiting factors hinder- 

 ing further development o 



It is obvious that new ideas and new methods must be en- 

 listed if we are to make further progress, and Mr, Eisenberg 

 has shown us today how he and his branch of the Hydromechanics 

 Laboratory are exploring the fundamentals of the subject. 

 Only in this way will we be able to proceed with confidence 

 to the attack on these new problems and the development of 

 rational design criteria for the use of the naval architect 

 and marine engineer » 



Mr 9 Eisenberg has more than once mentioned in his paper 

 the effect of air content of the water upon the incidence of 

 cavitation^ The program of experiments on propeller cavita,- 

 tion, carried out under the auspices of the I.TcT.Ca in many 

 propeller tunnels throughout the world, has shown the 

 critical importance of this factor and the need for its con- 

 trol in all experimental work. I was interested in 

 Mr, Eisenberg 's statement that, in his opinion, only the en- 

 trained bubbles and not the dissolved air contributed to 

 the inception of cavitation. This is a matter of some im- 

 portance to propeller tunnel work, for here we measure the 

 total air content. We are fully aware of the urgency of 

 the problem, as may be judged by the fact that in the new 

 36" propeller water tunnel we are to have a resorber neces- 

 sitating a pit 80' deep into the bedrock on which this sta- 

 tion is built o 



I would like to know if the author has any views on the 

 correct way to s cale cavitation phenomenon as they affect 

 propellers. At present we find the best correlation between 

 model and ship is found when we run the propeller in the tun- 

 nel at the highest possible water speed, ignoring all Froude 

 scaling, and adjustir'^ the revolutions Toer minute to slve 

 the correct slip. This gives relatively small pressure re- 

 ductions on the water, with the result that the water retains 

 the greater part of its air content. In connection with this 

 scaling problem, it may also be of interest to state that the 

 geometrically similar propellers used in the international 

 comparison, which range from 8 to I8 inches in diameter, give 

 considerable differences in performance. 



It is generally believed that the erosion damage on 

 propeller blades and on rudders and other fittings abaft 

 the propellers is due to the collapse of cavitation bubbles 



