Investigation of Asymmetrical Shaft Power Increase during Ship Maneuvers by means of Model Tests and CFD

Propulsion systems experience large power absorption fluctuations during tight maneuvers. In the case of a turning circle maneuver for a twin-screw ship, the power required by the two shaft lines can be completely different; in case of non conventional propulsion system, like cross-connect configurations, a compromise must be met in order to design a safe control system, without dramatically affect the vessel's maneuvering performance. In order to investigate the influence of different propulsion system operation settings on the vessel's maneuvering characteristics, a series of had-hoc free running model tests have been carried out at the CNR-INSEAN outdoor maneuvering basin. In the present work experimental results will be presented and discussed, focusing on the ship maneuvering performance under different propulsion system control settings. Moreover, CFD have been used to provide a deeper insight on the propellers overloading and unbalancing: first, numerical computations have been carried out to capture the nominal wake in correspondence of the propeller disks; then, propeller loads were evaluated (off-line the RANSE simulation) by means of two simplified model based on Blade Element Momentum theory (BEMT) theory