Statistical Correlations of Ship High-Run with Broaching-to and Capsize

In the current paper we are extending our earlier work on the assessment of a ship's tendency to capsize due to broaching-to in a stochastic seaway. Capturing, in a probabilistic context, interferences between different phenomena occurring during ship operation in extreme seas is a challenging task. Estimates of statistical correlations are deduced between high-run events, broaching-to and capsize. A phenomenological approach is adopted in this study for the classification of the targeted motions. Large scale simulations and a direct counting scheme are applied on the basis of a 4 degrees of freedom (4DOF) mathematical model for the coupled surge-sway-yaw-roll (and rudder) motions. Comparison with the results obtained from a previously used 3DOF model for the same scenarios is carried out in order to investigate the effect of roll on high-run's correlation with broaching-to. Additionally, sensitivity studies are carried out in order to examine the effect of the commanded heading angle, the rudder control gains and the threshold values defining excessive (unsafe) motions. The concurrence level of the three processes considered here is found to be significantly affected by the examined parameters. The paper includes a short review of effective methods for identifying ship high-runs in following/quartering seas.