The Influence of Freeboard on Wetness 



200 400 



SHIP LENGTH (Ft] 



600 



Fig. 9 - Curves of freeboard 

 ratio for constant probability 

 of wetness 0.60 C„ 



0-10 



ooa 



006 



0-04 



0-oe 



200 



400, 



SHIP LENGTH TPt) 



600 



Fig. 10 -Curves of freeboard 

 ratio for constant probability 

 of wetness 0.70 c„ 



the 0.70 Cg model tests. In Fig. 11, the slope of the lines of freeboard ratio for 

 constant probability of occurrence of wetness indicate that for ship lengths in 

 excess of 600 ft a constant freeboard gives equal probability. 



The question arises as to what is an acceptable level of probability of wet- 

 ness. At this stage it is difficult to say what is acceptable but ships which are 

 known to be good sea ships could be plotted in the diagrams in order to see what 

 level of probability would be expected for them. 



It is the intention to run models of the 0.60, 0.70 and 0.80 block coefficient 

 in irregular wave systems to check the number of times wetness occurs in a 

 given train of waves. The system of generating irregular waves in the Ship 

 Division's No. 3 Tank is such that the scale of the spectrum is easily modified. 

 A constant length model can therefore be used with varying scale of spectrum to 

 simulate different ship lengths. 



ACKNOWLEDGMENT 



This work has been carried out as part of the research programme of the 

 National Physical Laboratory, and the paper is published by permission of the 

 Director of the Laboratory. 



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