Abstract
This paper studies the hull girder strength check included in the new IACS Common Structural Rules (CSR). It first explains the ultimate limit state design and reviews briefly previous methods used to estimate the ultimate strength of ships. The net scantling approach used in the new Common Structural Rules is explained and its relation to the ultimate strength calculations. A program has been developed to calculate the vertical ultimate bending moment using progressive collapse method and applying the formulas presented in the new IACS (CSR) rules. The program is used to calculate the ultimate strength of three tankers of different sizes based on net scantling, net scantlings with 50% and 100% corrosion addition. A new design equation to predict the ultimate vertical bending moment based on net scantlings +50% corrosion addition is proposed.