Effect of Encountered Wave Condition on Fatigue Life Prediction of Ship Structures

Ship weather routing develops an optimum track for ocean voyages based on a forecast of weather, sea conditions, and a ship’s individual characteristics for a particular transit. In these days, most ships follow weather routing, and those ships never experience extremely severe seas. In classification society rules, ship structure fatigue assessment is performed without consideration of weather routing. In these assessments, the occurrence probability of severe seas is overestimated and their recurrence interval is underestimated. This might lead to deterioration in fatigue assessment precision. In this study, S–N-based fatigue assessments of a welded joint in a container ship that follows weather routing are performed. This ship sails on a North Atlantic Ocean route. Fatigue lives are evaluated assuming different encountered wave conditions: for a planned route, “Great Circle Route,” and a weather routing, “Minimum Time Route.” Short sea sequences are generated by a storm model using hindcast data. The storm profiles are determined by using the cumulative frequency of shot seas which is experienced on the MTR routes. Based on these results, the effect of encountered wave conditions on cumulative fatigue damage is discussed.