Plastic Collapse Strength of Hatch Cover of Bulk Carrier against Green Sea Load (1st Report)

Abstract

After the casualty of M.V.Derbyshire, United Kingdom insisted to increase the strength of a hatch cover of a Bulk Carrier to prevent the occurrence of similar casualties. This had been discussed at the International Association of Classification Societies (IACS), and a new unified rule, S21, came into effect. In the present paper, elastoplastic large deflection analysis is performed on two hatch covers of a folding type designed by the old rule in the International Convention on Load Lines (ICLL), 1966 and the new IACS rule, respectively. Based on observations on the simulated collapse behaviour by FEM, a simplified method is proposed to evaluate the plastic collapse strength of a hatch cover of a folding type. It is demonstrated that the proposed method gives accurate collapse load. At the end, strength of old and new hatch covers are assessed comparing the evaluated collapse strength with design loads specified by the rules. It is concluded that the hatch cover designed by the new IACS rule has appropriate and enough strength.