Prediction of Ship Slamming at Sea 



DISCUSSION 



E. V. Lewis 



Webb Institute of Naval Architecture 



Glen Cove, Long Island, New York 



This paper is of particular significance because it attempts to establish 

 criteria for the occurrence of slamming. Such criteria have been badly needed 

 in connection with the calculation of ship performance in irregular seas by the 

 method of superposition. The criteria will make possible, for example, the de- 

 termination of the speed at which slamming would become serious — or the pre- 

 diction of comparative slamming characteristics of alternative ship designs. 



It is hoped that for completeness the work will be continued to allow for the 

 effect of section shape on the critical vertical velocity for slamming — and also 

 to allow for the effect of form and fullness on the fore and aft location of the 

 critical section. 



The equations for various probabilities in evaluating performance in irreg- 

 ular seas will be very useful. It should be pointed out that the probabilities are 

 based on assumed stationary conditions — constant ship speed and heading, as 

 well as steady sea conditions. Hence, the equations must be used with caution. 

 For in the case of the full-scale ship at sea, the shipmaster is certain to change 

 course or speed if slamming becomes serious, so that conditions would not re- 

 main stationary. 



Another point is in regard to the assumption in the paper that the pressure 

 of water on deck is purely static. It would be expected that there would be con- 

 siderable dynamic effect associated with the aftward velocity of the water. 



DISCUSSION 



W. A. Swaan 



Netherlands Ship Model Basin 



Wageningen, Netherlands 



In the course of the last 10 years the possibilities of applying the super- 

 position theory or the problem of ship motions in irregular seas have covered 

 an increasing range of phenomena. At first only ship motions were considered, 

 subsequently the superposition methods for resistance and power were evalu- 

 ated and checked by experiments. The results presented in this paper here 

 cover the final gap, that is the relative motions at the bow with the associated 



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