The input data in hull girder bending strength calculation (e.g., bending moments, geometric and material properties) may have different levels of uncertainty. In most cases, the level of uncertainty of the result (e.g., stresses) is unknown. It can be calculated if the probabilistic distribution of the bending stresses is available. To derive this distribution, the composition of the distribution laws of the constituent variables is used. Examples for the application of the method are given for a 25K DWT bulk carrier.
In traditional calculations of the hull girder bending strength, data for the bending moments, section modulus and mechanical properties of the material are used. All these parameters have, in general, different probabilistic distributions. So, when the numerical results for stresses, deflections, etc. are derived, a question may arise as to what is the Level of Certainty (L.O.C.) of the result. Calculation of this certainty/uncertainty can be performed when the probabilistic distribution of the result is determined. As to the hull girder bending stresses, to determine their probabilistic distributions, one should know the probabilistic distributions of the hull girder geometric properties (in this case - Section Modulus) and the loads acting on it (still water, wave-induced and total bending moments). LEVEL OF CERTAINTY OF THE GEOMETRIC PROPERTIES The uncertainties in the geometric properties are not the dominant ones but they contribute to the total uncertainty of the final result. Therefore, it is worth studying these uncertainties to increase the accuracy in predicting the strength of, especially, aging ships. There are two major causes of the uncertainty in the hull girder geometric properties and its components - the manufacturing tolerances of steel plates and stiffeners and the corrosion wastage over time (the latter is the major contributor to this type of uncertainty).
