Simplified prediction methods for roll added inertia and effective wave slope coefficient of river-sea ships

The natural roll frequency and the effective wave slope coefficient are two essential parameters used in dynamic ship stability assessment. Although these parameters can be determined from direct hydrodynamic calculations or even experimentally, simplified semi-empirical methods remain a more practical choice for routine applications. However, suitable methods specifically tailored to river-sea ships, which are essentially inland vessels complying with additional requirements for navigating in maritime stretches, are still lacking. Existing semi-empirical prediction methods have been typically developed for conventional sea-going ships, thus applicability to river-sea ships is limited due to the significant differences in hull forms. To fill this gap, this paper presents regression formulae for added inertia, intended for use in predicting the natural roll frequency, as well as formulae for the effective wave slope coefficient at the natural roll frequency and for the frequency-dependent effective wave slope coefficient. The dataset for the development of the regressions is based on direct 3DOF linear hydrodynamic calculations. The performance of the developed formulae is evaluated both against the training data and independent test vessels. Results demonstrate very good agreement with directly computed values, indicating that the proposed formulae represent a promising tool for supporting dynamic stability assessment of river-sea ships.