With the effectuation of U.S. OPA"90 (1990), all new tankers must have double hull arrangement if they are going to operate in the U.S. waters. The International Maritime Organization (IMO,1991) is also legislating the same requirement which is to be applied in the worldwide sea. Contrary to. our expectation, there is a lot of experience in the design and construction of double hulls. The existing design criteria or methods which have been provided a rational design guide are also available for the design of the double hull tanker. Nevertheless, we are feeling that the construction of the double hulls is very new and needs more advanced technology. This perception may be partly true because: In the structural design of double hull tanker, the scantling of local members is determined by usual procedures or existing rules of classification societies. Thus it may be expected that local members or local structures have relatively sufficient safety. However, since a large change of structural arrangement is made, compared to the conventional tanker, it is not sured that the whole structure has sufficient redundancy in both intact and damaged conditions. In this regard, safety evaluation for the whole structure on the basis of ultimate strength is required. In the present study, ultimate hull girder strength analysis in the intact and damaged conditions is conducted using ALPS/ISUM computer code (Paik,1991) which has been developed using the idealized structural unit method. The objective ship is a double hull tanker of 40,000 dwt with a transverse less structural system (Okamoto et al,1987). The effect of some factors affecting ultimate hull girder strength is investigated through sensitivity studies. Based on the results obtained here, the reserve strength measure for the intact hull and the residual strength measure for the damaged hull are discussed.

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