ABSTRACT

After a brief introduction of structural design procedure for double hull tankers, their design features are firstly highlighted comparing with conventional single hull tankers. Next discussed are recent topics of double hull VLCC (= Very Large Crude oil Carrier) including higher tensile steel and strut arrangement in transverse ring frames. Finally ultimate longitudinal strength of hull girder is analysed through a simplified method under both sagging and hogging conditions. Making use of this result, some considerations are made on structural reliability of double hull VLCC.

INTRODUCTION

It became compulsory for newly built oil tankers to adopt double hull structure or equivalent in order to prevent oil pollution in the sea environment.MES (= Mitsui Engineering & Shipbuilding Co., Ltd.) has successfully delivered several double hull tankers of Suez Max., Afra Max. and a smaller size Shuttle Tanker so far. Concerning double hull VLCC, basic design works have been completed. Based on these experiences, new aspects of structural design of double hull tankers are discussed. Because there exist already double hull structures such as container vessels, open bulk carriers and so on, double hull tankers are not an entirely new concept. But there may be many design alternatives when applying today's advanced technology. This paper first introduces the change of structural configurations depending on the vessel's size and some features of structural design procedure comparing with conventional single hull tankers. Next discussed are recent topics of double hull VLCC. A large number of ageing single hull VLCCs built during 1970's are expected to be replaced in near future. In response to this potential demand, basic design of double hull VLCC has been already completed, where rational structural arrangements are investigated considering structural reliability and costs. One of big concerns among ship owners is recent extensive usage of higher tensile steel, though the final material selection rests with owners.

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