Investigation of twin screw naval ships manoeuvrability behavior

The problem of ship manoeuvrability has reached nowadays a significant consideration, both for merchant ships, with the adoption of IMO standards, and naval ships, with the production of various documents by NATO Specialist Teams. In literature many works regarding manoeuvrability of single screw slow/medium speed ships are present, while a lack of information about twin screw ships (cruise ships, RoRo ferries, megayachts, naval vessels) exists. These ships are usually characterised by different hull forms and more complex stern configuration due to the presence of appendages like skegs, shaft lines and brackets, which can strongly affect manoeuvrability behaviour. In this work various prediction methods, namely statistical regressions, system identification and RANSE, have been investigated in order to evaluate twin screw naval vessels manoeuvrability behaviour. From this analysis stern appendages influence (including also non linear effects resulting from hull-appendages interactions) resulted one of the peculiar characteristics of this type of ships, clearly affecting their manoeuvring capabilities.