DISCUSSION ON HYDROELASTIC CONTRIBUTION TO FATIGUE DAMAGE OF CONTAINERSHIPS Quentin Derbanne a , François-Xavier Sireta a , Fabien Bigot a and Guillaume de Hauteclocque a a Bureau Veritas ABSTRACT Full scale monitoring campaigns and model tests have shown an important high frequency contribution to fatigue damage, coming from the global wave induced ship vibrations. This high frequency contribution is often assumed to be the hydroelastic contribution. Numerical models are able to separate the quasi-static response from the total hydroelastic response. It is shown that the total linear hydroelastic contribution is the combination of three different hydroelastic effects: hydrostatic relaxation, low frequency dynamic amplification, and high frequency resonance. Computations have been done for 6 container ships and linear long term fatigue damage is computed based on bending moment and torsion RAOs. The conclusion is that for vertical bending damage the hydrostatic restoring effect and the low frequency dynamic amplification effect are cancelling each other: the total hydroelastic contribution is equal to the high frequency contribution. However for torsion damage there is no hydrostatic restoring effect and an important part of the hydroelastic effect is located at low frequency: the total hydroelastic contribution to fatigue damage is larger than the pure high frequency contribution. KEYWORDS Fatigue damage; Springing; Containerships; High frequency; Quasi-static; Hydroelasticicty; Bending moment; Torsion 1 INTRODUCTION The increased size of the recent Ultra Large Container Ships and LNG ships reactualizes the hydroelastic wave induced type of ship structural responses. Usually the hydroelastic ship response is divided into springing and whipping, springing being defined as the steady ship vibrations induced by non-impulsive wave loading and whipping as a transient vibratory ship response induced by impulsive loading such as slamming. In the past few years many measurement campaigns have been done on several containerships sailing all around the world. Ito & al. 1 analyzed some measurement on a 278m containership sailing in 5m significant wave height. They showed that the contribution of high frequencies (HF) to the total fatigue damage is between 30% to 40%. Oka & al. 2 showed that for a post panamax containership, after two and a half year of navigation between Japan and Europe, 46% of the fatigue damage is due to the HF content. Koo and al. 3 have the same result of 28% HF contribution after 28 months of navigation of a 8000 TEU container vessel. Storhaug & al. 4,5