Prediction of Ship Slamming at Sea 



Fig. 9 - Connparison between experimentally 

 obtained histogram! of slamming pressure 

 and predicted probability density function 

 (mild Sea State 7, ship speed 10 knots, 

 light draft) 



of slamming is considered as a Poisson process, then the time interval between 

 successive slams is a random variable which must follow an exponential proba- 

 bility law theoretically [8]. 



In order to obtain an answer to the above question and thereby to determine 

 the probability density function for the time interval between successive slams, 

 a sample of the time history of slamming obtained in tests conducted on a MAR- 

 INER model will be shown. 



Figure 12 shows the time history of slamming pressure (converted to full 

 scale) measured at 0.1 L aft of the forward perpendicular in a severe Sea State 7 

 at a 10-knot ship speed [4]. The ship was in light draft condition; specifically, 

 40 percent of cargo loading. A total of 84 slams were observed during 203 cy- 

 cles of wave encounter in a 31 min-7 sec observation. It is noted that the sam- 

 ple shown in the figure is the composite of four records taken in the tests. 

 Hence, there exists three points of discontinuity as marked in the figure. Al- 

 though the tests were carefully conducted, there is a possibility that several 

 wave encounters and a small amount of time were lost at these discontinuities. 

 The vertical line marked in the figure indicates a slam whose pressure magni- 

 tude is proportional to the height of the line. The black circles indicate wave 

 encounters without slamming. 



563 



