Recently, there are some Classification Societies which approve exposed hatch covers of non-weathertight construction with no packing. However, it is necessary to prove no possibility that cargo holds might be flooded by deck wetness when such a vessel as is provided with non-weathertight hatch covers is navigating under the bad sea condition. The method of predicting the short term probability of deck wetness is applied to calculating how much amount of water leakage can arise from omitting packings. As the result of the study, we obtained a practical way of predicting water leakage into cargo holds through the clearance between hatch covers and coamings. Actual calculations show that water leakage, for example on the container ship with a comparatively high freeboard, is so little that non-weathertight hatch covers can be adopted. We believe that these results can bring less initial cost and also less maintenance not only to shipyards but also to ship operators.
