Auto -os dilations of Anchored Vessels 



coastal buoy, which I mentionned earlier, the sway oscillations to- 

 tally disappear in I meter waves. 



The authors discussed fully the influence of the position of 

 the centre of pressure of the superstructures on the stability of the 

 equilibrium position. I would like to know the effect of pre stretching 

 the chain on the ship oscillations. 



REPLY TO DISCUSSION 



N. N. Rakhmanin 



Kryloff Ship Research Institute 

 Leningrad* U.S.S.R. 



First of all I must thank Dr. Dern for his comments. I 

 should like to make two remarks about them and to answer them. 



When we compare the behaviour of a vessel with a buoy we 

 must remember that the buoy has a small LB ratio, which is about 

 I. As to the conventional fishing vessel, her length breadth ratio is 

 about 5 or more. In the Paper there is an indication that this LB 

 ratio has an influence on the oscillation. To my mind these auto- 

 oscillations of a conventional vessel and a buoy have a different cha- 

 racter. The auto -oscillations of a vessel, I described in detail in the 

 paper, are connected with the quality of a vessel to turn across the 

 flow, when being the free floating body. Such body has a steady equi- 

 librium position when it is located across the flow. 



_ As to the oscillations which one can observe at a buoy in the 



current, to my mind the cause of these oscillations is connected with 

 another phenomenon. This phenomenon is the vortex separation be- 

 hind the cylindric body of a buoy. The eddies separate in turn from 

 the left-hand and the right-hand side of a buoy. As it appears to me 

 that such character of the vortex separation causes the transverse 

 periodic forces to excite the buoy oscillations. 



Another point concerns the comparison of the results of the 

 theoretical calculations and that of the experimental data. I must say 

 that this investigation has been started not from a theoretical consi- 

 deration but from the full-scale observation of the fishing vessel 



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