A BRIEF SURVEY OF PROGRESS ON TIIE MECHANICS OF CAVITATION 



by 



Phillip Elsenberg 

 David Taylor Model Basin Report Noo 8^2, October 195? 



DISCUSSION 



Dr. F. Ho Todd, Chief Naval Architect, David Taylor Model Basin. 



Cavitation is a phenomenon of great importance to the 

 naval architect and it may be of interest to summarize some 

 of the effects it may have on ships, their propellers, and 

 appendages o The first, and most serious of these, occurs 

 in cases of well- developed propeller cavitation in which 

 there may be a considerable loss of thrust and therefore of 

 speed. This was first noticed in the trials of the British 

 destroyer "Daring" about l892« Cavitation on such propel- 

 lers also gives rise to hull vibration and to damage to the 

 blades of the propellers » This latter takes the form of an 

 erosion which may develop very rapidly and make frequent re- 

 newals of propellers essential. Cases are on record where 

 trans- Atlantic liners have had to have new propellers after 

 no more than two round trips across the Atlantic and of des- 

 troyers which have shown the beginning of propeller blade 

 erosion after only two hours at full power » Concurrently 

 with vibration and erosion, cavitation also gives rise to 

 undesirable hydrodynamic noise. The lifting surfaces on 

 hydrofoil boats also suffer from cavitation as the foils 

 approach the surface and thus may give rise to instability 

 in the motion of the praft. It may be said therefore that 

 cavitation is an unmitigated nuisance to the ship and pro- 

 peller designer© 



In the past we have generally been able to reduce the 

 effects of cavitation by good design practices, such as 

 larger propeller blade area, the use of constant pressure 

 sections, and careful attention to the shape of the lead- 

 ing edge of the blades, but we are now entering the region 

 where these solutions are becoming less useful o Thus, in 

 destroyers and carriers, we must already accept some loss 

 of speed at the top powers, while in high-speed motorboats 

 the propellers are actually working in the fully- cavitating 

 or super- cavitating region; that is^ where the whole of the 

 back of the blades is denuded of water with a consequent 

 great decrease in efficiency. This latter may be as low as 

 30-35^!) although it does result in relative immunity from 

 erosion of the blades o Cavitation from propeller blades or 



