Fatigue reliability of the ship hull girder accounting for inspection and repair

A formulation is presented for the assessment of the reliability of a ship hull with respect to fatigue failure of the longitudinal members. The model allows for the existence of multiple cracks both in the stiffeners and in the plating and it models the crack growth process. The effect of the cracks on the midship section modulus is modelled as a function of time and the resulting reliability is quantified. It is assumed that the inspection method is perfect and detects all cracks larger than a detection limit, which in turn is method dependent. Detected cracks are subjected to a perfect repair being restored to the initial crack size. The effect of hull maintenance is seen in the step changes of the reliability function. The sensitivity of the reliability estimates with respect to several parameters is also studied.