A Survey of Ship Motion Stabilization 



I want to compliment the authors for an interesting and informative paper. 

 The paper by being a survey is a mine of information on a wide range of topics, 

 having to do with ship motion stabilization. 



DISCUSSION 



A. Silverleaf 



National Physical Laboratory 



Teddington, England 



This interesting survey is almost as surprising for its omissions as for the 

 topics which it discusses at some length. For instance, it is more than surpris- 

 ing to find no reference to the paper by the late J. F. Allan, "The Stabilisation 

 of Ships by Activated Fins," Transactions of the Institution of Naval Architects, 

 1945, Vol. 87, which was the first published account of the modern development 

 of the type of roll stabiliser still that most commonly used and adopted. 

 The authors' suggestion that the design of activated fin stabilisers has developed 

 in an unscientific manner is completely contrary to the facts. Activated fin sta- 

 bilisers of the type now known as the Denny-Brown-A.E.G. have been continu- 

 ously developed for the past 25 years by a skillful and systematic combination of 

 theory, model experiment and full scale practice. This applies not only to the 

 activating and control mechanisms but also to the basic hydrodynamic design of 

 the fins themselves, for which in 1942 I developed an inverse Theodersen pro- 

 cedure for designing foil shapes with delayed cavitation characteristics. Similar 

 methods were being independently and simultaneously developed for aerofoil 

 sections and have produced among other things the well known "flat top" sections. 

 The authors' doubts about the value of roll stabilisers of this type were certainly 

 not endorsed by the crews of the ships of the Royal Navy fitted with such stabi- 

 lisers during the Second World War; in many cases they were the only ships able 

 to offer any effective defence against air attack because they provided a reason- 

 ably stable firing platform. 



The authors' discussion of roll stabilisers of the passive tank type is of 

 great interest to us at N.P.L., where such stabilisers have been designed for 

 some time. It is our growing opinion that a wide variety of shapes and configu- 

 rations can be effectively used for this purpose, and indeed it is almost true to 

 say that only a very good man can design a really bad system. Dr. Kaplan's 

 reference to activated pitch stabilisers revives interesting memories for me. 

 Almost seven years ago Mr. Goodrich and I took out a provisional patent for just 

 such a stabiliser, incorporating a jet flap, but allowed it to lapse because we 

 found great difficulty in producing a system of reasonable overall mechanical 

 and hydrodynamic efficiency. Naturally we shall be most interested in this new 

 attempt to exploit this attractive idea. However, I might venture a word of 



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