PREDICTION OF OCCURRENCE AND 

 SEVERITY OF SHIP SLAMMING AT SEA 



Michel K. Ochi 



David Taylor Model Basin 



Washington, D.C. 



ABSTRACT 



Basic properties which govern ship slamming in rough seas are dis- 

 cussed from theoretical consideration. Specifically, the probability of 

 occurrence of slamming, magnitude of impact pressure associated with 

 slamming, and time interval between successive slams are studied 

 from a statistical approach, and formulae are derived for the predic- 

 tion of these events. The prediction method is also applied to the prob- 

 lem of deck wetness caused by shipping of green water at sea. Theo- 

 retical results are compared with those obtained in experiments 

 conducted on a MARINER model in rough seas. 



INTRODUCTION 



When a ship navigates at certain speeds in rough seas she frequently expe- 

 riences slamming at which time the forward bottom sustains large forces re- 

 sulting from the impact. 



Slamming occurs at random at sea. The severity of slamming and time in- 

 terval between two successive slams are also at random. Sometimes a ship 

 may slam successively with varying intensity; while again no slamming may 

 occur for a relatively long period of time and then suddenly a severe slam oc- 

 curs. In statistical terms slamming is a random phenomenon, and the severity 

 and time interval between successive slams are random variables. For this 

 random phenomenon, only one study has appeared in the literature as of this 

 date. This study made by Tick concerns the prediction of the rate of occurrence 

 of slamming at sea [1]. 



The purpose of the present paper is to develop a method for predicting the 

 probability of occurrence and severity of slamming, and the time interval be- 

 tween successive slams in rough seas. Specifically, it is the intent of this paper 

 to predict the following: 



(a) Probability of occurrence of slamming for given conditions, such as for 

 a given sea state, course ar^le, loading condition, etc. 



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