The heel influence on ship manoeuvrability: Single and twin-screw surface vessels

Low transverse metacentric height and high speed are peculiar destabilising factors in ship manoeuvrability according to the attainable large heeling angles. The phenomenon indeed occurs in the case of vessels characterised by loading conditions with low transverse stability - e.g. high centre of mass of container vessels and RoRos. Starting from Kijima's single-screw container vessel evidence, an extension of the study to twin-screw ferry vessels is undertaken, with the scope of quantifying its effect in terms of turning and zig-zag IMO margins at an early design stage. Given the relevant impact, an enlarged captive model testing campaign executed on a sample of reference vessels was analysed to further characterise and extend the concepts to a broader class of modern single and twin-screw vessels, thus motivating the study. As a further result, this analysis allowed to underline the need of a review of the IMO intact stability code when dealing with heeling angle during a turn.