Semi-probabilistic approach for assessment of the requirement for minimum hull girder section modulus

Abstract

The paper presents a study on an approximate semi-probabilistic approach for assessment of any given requirement for minimum hull girder section modulus (HGSM). It consists of calculating the HGSM using as input data the reduced (due to corrosion) plates’ thicknesses and longitudinals’ cross-sections with exactly the same probability of exceedance. Its accuracy is checked against results obtained by the complete probabilistic approach developed by the author. In this paper, the requirement for minimum HGSM is based on the IMO (International Maritime Organization)-formulated permissible reduction by 10% of the as-built HGSM. A numerical example is given for a bulk carrier of 25,000 deadweight ton (25K DWT). A comparison between the results obtained by the complete probabilistic method and those obtained by the semi-probabilistic method showed that the accuracy of the semi-probabilistic method is around +8% when the 95th percentile of the corrosion wastage of plates and longitudinals is used, and around −2% when the 99th percentile of the corrosion wastage of plates and longitudinals is used. The semi-probabilistic approach is simpler than the complete probabilistic approach but has relatively high accuracy, especially for higher-order percentiles, and thus is recommended for practical use.