A guide for the ultimate longitudinal strength assessment of ships

The aim of the present paper is to establish a practical guide for the ultimate longitudinal strength assessment of ships. The ultimate hull girder strength of a ship hull can be calculated using either the progressive collapse analysis method or closed-form design formulas. In the present paper, both the progressive collapse analysis method and the design formulas are presented. A comparison between the progressive collapse analysis results and the design formula solutions for merchant cargo ship hulls is undertaken. The total design (extreme) bending moment of a ship hull is estimated as the sum of the still-water and wave-induced bending moment components as usual. The safety measure of a ship hull is then defined as a ratio of the ultimate longitudinal strength to the total design bending moment. The developed guidelines are applied to safety measure calculations of merchant ship hulls with respect to hull girder collapse. It is concluded that the guidance and insights developed from the present study will be very useful for the ultimate limit state design of newly built ships as well as the safety measure calculations of existing ship hulls. The essence of the proposed guide shall form ISO code 18072-2: Ships and Marine Technology-Ship Structures-Part 2: Requirements of Their Ultimate Limit State Assessment.