ASPECTS OF A RELIABILITY CALCULATION PERFORMED ON AN OIL TANKER

The paper presents some results of a reliability analysis carried out on a 150,000 DWT double hull tanker. The analysis is performed according to a second level reliability procedure and a description is contained of the stochastic model for the considered variables. In particular, a detailed comparison is made on the results obtained with various degrees of approximation in the model for sea loads. A typical route between Northern Europe and the Persic Gulf via the Suez Channel is considered in the study, which is relative to a period of one year. In the description of loading and operational conditions, use is made of detailed records available from the owner, regarding the first year of activity of the ship. The ultimate collapse value of the hull girder in its “as-built” condition and the failure mode due to vertical bending moment are considered in the collapse equation. The present work gives an indication on the procedure that can be followed in the reliability analysis of a ship, as well as on the values of the reliability index obtained for an existing, typical and well designed oil tanker in a typical route. Such values can be used for future comparisons between different design solutions or practices. The results of the present study can also be used to calibrate a first order reliability model (partial safety factor format).