Criteria for parametric roll of large containerships in longitudinal seas. Discussion

This paper discusses the technical background of the American Bureau of Shipping (ABS) Guide for the Assessment of Parametric Roll Resonance in the Design of Container Carriers. The paper, which follows the structure of the proposed Guide, begins with an explanation of the physics of the parametric roll resonance phenomenon in longitudinal (head and following) waves. This explanation does not use any mathematical models and was designed to be accessible to engineers with a variety of backgrounds. The paper has two main foci: first, the establishment of Susceptibility Criteria that can be used to determine if there is danger of parametric roll and, second, a description of methods for calculating amplitude of parametric roll in longitudinal waves that serves as a Severity Criterion. Verification of the both criteria has been done using the Large Amplitude Motions Program (LAMP), one of the most sophisticated general seakeeping simulation codes available. The paper describes the verifications that were performed, which showed that the criteria provided a very reasonable means of predicting the likelihood of occurrence of the phenomenon. The paper also discusses probabilistic aspects of numerical simulation of parametric roll in irregular waves, and examines methods of probabilistic treatments of parametric roll.