Giddings and Wermter 



caution. While many devices, including bulbous bows and fins, show a reduction 

 in pitch in regular waves, this improvement is often not shown in terms of sig- 

 nificant motions in irregular waves. General experiments in regular waves are 

 not carried out in long enough wave lengths in which these devices can show un- 

 desirable response characteristics; experiments in irregular wave systems in- 

 clude the responses to such wave lengths. 



REPLY TO THE DISCUSSION 



Alfred J. Giddings 

 Bureau of Ships 

 Washington, B.C. 



and 



Raymond Wermter 



David Taylor Model Basin 



Washington, D.C. 



The authors' are pleased with the response to the paper. Mr. Ripley's re- 

 marks are appreciated, as coming from one who re-initiated the interest in 

 passive tank stabilization. 



The additional information on anti-pitching tanks presented by S. Motora is 

 especially interesting. Continued work on this line may well lead to much im- 

 proved seakeeping, at least for special ships. 



Mr. Dalzell's recent work on the details of anti-roll tank dynamics is 

 somewhat discouraging in that the nonlinearities inherent in the phenomenon 

 are confirmed. The simplified analyses that have sufficed for design in the 

 past, must be replaced by more elegant processes to realize the full potential of 

 passive tanks. 



The state of the art in fin stabilization as discussed by Commander DuCane 

 continues to advance. The reduction of design fin capacity as advocated by the 

 Commander, is not endorsed by the authors. There may be cases, for ships 

 with very long roll periods, wherein the fin capacity is not so readily taxed, but 

 for most ships, saturation would defeat the value of the fins. It is agreed that 

 the circumstance associated with the occasional very large roll should be clari- 

 fied. 



Fin effectiveness in a following sea is reduced by the orbital velocity of the 

 water, and by the difficulty of designing a control system to cope with low fre- 

 quency disturbances as well as the more usual frequencies. 



812 



