Structural Fatigue Life Assessment and Sustainment Implications for a New Class of US Coast Guard Cutters

This paper presents an overview of the US Coast Guard’s Fatigue Life Assessment Project (FLAP) and the application of the results in hull structure lifecycle management of the National Security Cutter class. One of the key measurements of the FLAP instrumentation included a radar based wave data measuring system. These measurements were used to determine the operational profile and wave statistics the Cutter encountered for the first five years of service. This information was compared to the design assumptions to understand the differences between design, actual operations, and impact on the long term fatigue damage forecasts. The influence of the operator is discussed. The model tests, dedicated trials and long term monitoring provided valuable insights into the limitations of analysis and predictions. A reliability based fatigue life prediction approach is discussed, along with how they may be used to evaluate options for life cycle management of fatigue and the Return on Investment (ROI) for considering fatigue early in the design. Finally, conclusions and recommendations are provided for the advancement of the spectral fatigue approaches for cost effectively managing fatigue in ship structure.