Previous speakers have suggested that varying the proportions of the ship can 

 achieve an improvement, but from the practical point of view the possibility of pursuing 

 that line is distinctly limited. 



As regards rolling, the natural damping factor is small, and while it would be 

 possible to increase this factor greatly by giving the ship, for example, large bilge 

 protuberances, from the practical point of view this has never been pursued, because 

 it would interfere both with the propulsive characteristics and the handling of the ship. 



The rolling problem has been substantially solved by the introduction in Great 

 Britain of the controlled fin stabilizer, which increases the damping factor to such an 

 extent that rolling is substantially eliminated. 



Having successfully controlled rolling, one's ideas naturally turn to the question 

 of pitch and heave reduction. It is an open question whether the shape of the ship 

 can be so modified to increase the damping factor in pitch and heave, without paying 

 a large penalty from the propulsion point of view. 



If one applies controlled damping, in the form of controlled fins or other means, 

 the question of the time element is of quite considerable significance. In other words, 

 one must operate the control and produce the variation of the force on a time plan 

 which matches the pitch frequency. As you are aware, this frequency is about twice 

 that of roll and the problem is correspondingly more difficult. 



A question, perhaps more properly discussed tomorrow morning, is that of 

 driving ships very hard in bad weather conditions, which is of considerable interest in 

 view of the possibility of largely increased driving power. If one equips a ship with a 

 controlled mechanism which stops rolling and damps pitching, it is quite probable that 

 one will be able to drive it successfully through very bad seas. 



But there is a very serious practical point which arises, and that is, what hap- 

 pens if the control mechanism fails? The ship might meet catastrophe before the 

 position could be rectified. 



It may be of interest to note that the "Queen Elizabeth," which is equipped 

 with roll stabilization, can be driven at full speed in conditions which would require a 

 reduced speed if there was no stabilizer, but the captain is worried as to what would 

 happen if the machine suddenly ceased to function in such circumstances. Reliability 

 is of paramount importance. 



M. C. Eames 



Regarding Dr. Kaplan's amplification of Dr. Weinblum's reference to the study 

 of the seaworthiness of hydrofoil craft, it is felt that one point should be clarified. 

 Dr. Kaplan has quite rightly pointed out that a linearized quasi-steady theory of the 

 pitching and heaving response of hydrofoil has proven inadequate for predicting the 

 motions of such craft in regular seas. 



The experimental work on which this conclusion is based, however, covered a 

 necessarily limited range of wave conditions and craft speed. There is reason to 

 believe that once the craft is well clear of conditions of resonant response, the linearized 

 quasi-steady theory proposed by Dr. Weinblum suffices to give a very reasonable 

 approximation to the true motion. 



This in no way detracts from the remarks of Dr. Kaplan and his very fine 

 work on the effects of unsteady motions. The most important case does, of course, 

 correspond with resonant conditions and the correct prediction of the the motions 

 resulting from such conditions is vital to the safe performance of hydrofoil craft. 

 Unless the writer misunderstood the speaker, however, there was a hint that the more 

 elementary approach should be discarded altogether, and it is felt that insufficient 

 experimental evidence has been obtained to date to justify this. 



Possibly this represents the wishful thinking of a simple-minded hydrofoil craft 

 designer, but the feeling nevertheless remains. 



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