Investigation of Twin-Screw Naval Ships Maneuverability Behavior

The problem of ship maneuverability has currently reached 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 maneuverability of single-screw slow/medium speed ships are present, while a lack of information about twin-screw ships (cruise ships, Ro/Ro ferries, megayachts, naval vessels) exists. These ships are usually characterized by different hull forms and more complex stern configuration because of the presence of appendages such as skegs, shaft lines, and brackets, which can strongly affect maneuverability behavior. In this work various prediction methods, namely statistical regressions, system identification, and RANSE, are investigated to evaluate twin-screw naval vessels maneuverability behavior. Results of this analysis clearly evidence importance of stern appendages influence on maneuverability capabilities of this type of ship (including also nonlinear effects resulting from hull/appendage interactions).