Giddings and Wermter 



fins is highly effective and universally popular. This is where the acceleration 

 term can help by incorporating an element of phase advance and getting things 

 moving in plenty of time. 



Incidentally we as a firm always point out that good as they may be fins do 

 not, of necessity, reduce the incidence of sea sickness and it is a somewhat 

 dangerous policy to say they do because it is probably more the pitching accel- 

 erations which cause the trouble. 



It is probably time that "stabilising" devices were offered subject to per- 

 formance specifications as the present method of advertising the optimum re- 

 duction percentage under ideal conditions, or at least specially selected condi- 

 tions is meaningless and misleading. 



The difficulty here, of course, is in specifying, in a meaningful way, the 

 seaway in which the performance specified should be achieved and furthermore 

 in recording the nature of the actual sea in which the performance is achieved. 



Though without first hand experience it must surely be a somewhat sobering 

 thought that at the very low frequencies experienced in quartering seas in the 

 Western Ocean there is quite a likelihood, if not certainty, that the water in any 

 passive tank will provide an unstabilising moment just at the wrong time. 



Again I thank the authors. 



DISCUSSION 



John F. Dalzell 



Southwest Research Institute 

 San Antonio, Texas 



The discussor would, in all sincerity, like to compliment the authors on one 

 of the most straightforward and informative papers on the subject to come his 

 way in some time. The authors' summary of the work on passive anti-roll tanks 

 at Southwest Research Institute is adequate and exactly to the point. We have 

 recently submitted a draft Technical Report* summarizing our efforts in this 

 field which concludes, as did the authors, that a nonlinear model must be dis- 

 covered before any significant gain over present design methods can be fore- 

 seen, and that experiments will continue to play a large part in passive anti-roll 



'■'Studies of Ship Roll Stabilization Tanks, Technical Report No. 1, Contract NONR 

 3926(00), by John F. Dalzell,_ Wen-Hwa Chu, J. Everett Modisette, Southwest 

 Research Institute, August 1964. 



802 



