Progressive Collapse Method (PCM) has been broadly applied to predict moment-carrying capacity of a hull girder, however accuracy of PCM has not been much studied. Accuracy of PCM is known to be dependent on how Load-Shortening and-Elongation (LSE) curve of a structural units are well predicted. This paper presents a new procedure to determine LSE datum based on box girder Finite Element Analyses (14hAs) instead of using finite element model of stiffened panels. To verify reliability of PEA results, the simple box girder collapse test results are compared with FEA results of same box girders. It reveals one frame-based box girder model is sufficiently accurate in terms of ultimate strengths of the box girders. After extracting LSE data from the box girders, PCM-based moment-carrying capacities are compared with those from FEAs of the box girders. PCM results are found to be equivalent to FEAs in terms of moment-carrying capacity if accurate LSE data are secured. The new procedure is applied to well-known 1/3 scaled frigate full section. Very excellent moment-carrying capacity of frigate hull section is obtained from PCM with LSE data from box girder FBAs. Copyright (C) 2016 Society of Naval Architects of Korea. Production and hosting by Elsevier B.V.