Johnsson and Stfntvedt 



Figure 37 and other Figures in the present paper show, however, 

 the striking influence of cavitation on the surface forces in the present 

 case. As an influence of cavitation of similar magnitude is not expect- 

 ed for the bearing forces our conclusion is that, in cases where the 

 volume variation of the cavitation is important, the surface forces 

 will be predominant. 



DISCUSSION 



Finn C. Michel sen 



Norges Tekniske H0gskole 

 Trondheintj Norway 



I do not know how far back my historical recollection goes. I 

 was not at the London meetings, so I do not know what our colleague 

 Professor Telfer said, but I do know that the fin has been used on 

 Great Lakes carriers for some 20 years and that in fact, a paper was 

 published on the subject in the Transactions of the Society of Naval 

 Architects and Marine Engineers around 1950 by Professor Baier and 

 Professor Ormondroyd. I believe the authors obtained a patent on this 

 fin. The success of the fin is demonstrated clearly by the fact that 

 these fins are still being installed on Great Lakes carriers, especial- 

 ly when they are repowered, so there is nothing new in that respect. 

 I wish , however , that proper reference had been made to in the pre- 

 sent paper to the work by Baier and Ormondroyd. I do not know whether 

 Baier was the first inventor but he was at least a successful applicator 

 of the fin. There is one phenomenon I should like to mention in connec- 

 tion with these fins, something that was said to occur on the Great 

 Lakes carriers. The vibration level on these ships prior to installa- 

 tion of fins is usually not steady. It seems to build up a peak level 

 about every 10 seconds, followed by somewhat of a lull. On a model 

 we have discovered vortices that attach to the model on one side or the 

 other and would sort of peel off into the wake, and this is apparently 

 associated with these high level vibrations. The fin seems to affect 

 the flow around the stern in a very large or significant way through 

 the elimination of such vortices. I wonder if that is the phenomenon 

 we are faced with there. The fact that the authors do not see any dif- 

 ference in the cavitation patterns in five bladers, six bladers and so 

 forth may be an indication of this. 



I should also say that the measurements on the Great Lakes 



662 



