Abstract:  Based on the descriptive statistical analysis for the alternating stress range data，this paper suggests to model the data by a class of normal mixture distributions with two peaks．The parameter of the mixture distribution can be estimated by the EM algorithm. Employing the estimated parameter values of the mixture distribution，some inherent relationships of the fatigue loads in different parts of the hull under certain conditions were revealed．The waveinduced hull stresses are particularly complex at the bow，symmetric normal inverse Gaussian mixture distributions are more suitable to fit the alternating stress range data．The empirical analysis shows that the parameter of the proposed probability distribution can reflect the size of the fatigue loads in different parts of the hull，and the conclusion of inherent relationships of the fatigue loads in different parts of the hull provides a theoretical foundation for the operation quality research of the ship．

Key words: container vessel, mixture model, normal inverse Gaussian, fatigue damage, stress analysis