ABSTRACT

The problem of fatigue has been very critical for ship owners, designer, classification society etc. in shipbuilding industry. The assessment procedure for fatigue strength is complicated and a time- consuming job, but, for the maintenance purpose, it is a very critical item. Main target of present study is to calculate the fatigue life of longitudinal members amidships, where an LNG vessel is addressed as a case study using simplified fatigue method, which is based on DNVGL Classification Note 30.7: “Fatigue Assessment of Ship Structures”. A full load condition and a ballast condition are investigated with respect on fatigue damage assessment. Fatigue life is computed for selected longitudinal connections, amidships and 25-year designed life is aimed with North Atlantic wave environment. For the most of the details examined, the fatigue lives are found above 25 years using an efficient coating life of 15 years. The lower side, bottom and hopper plate longitudinal connections to web frames indicate fatigue lives below 25 years. If an effective coating is maintained during the entire lifetime of the vessel, only lower side and lower part of hopper plate longitudinal connections at web frames would need modifications. Repair proposals are given for those details having fatigue lives less than 25 years in the end of the study.