Analysis of Asimmetrical Shaft Power Increase During Tight Manoeuvres

In the present work the phenomenon of asymmetrical shaft power increase during tight maneuvers is investigated by means of the analysis of turning circle maneuvers at different speeds and rudder angles performed during sea trials for a series of twin screw naval ships; this analysis has allowed to underline a common trend for asymmetrical shaft power increase despite significant differences in ships considered; possible reasons for this shaft power increase have been examined, and data about an asymmetrical variation of wake fraction during maneuvers are reported, showing again a common trend but with larger scatter of data. In this view, a first investigation about the possibility of performing dedicated free running model tests and scaling their results to full scale, in order to improve prediction accuracy for a specific ship in preliminary design phases, has been carried out. It is believed that, for unconventional propulsion plant arrangements, in which for instance two shaft axes are powered by the same prime mover via a unique reduction gear, automation plant will need to monitor carefully these effects, in order to avoid possible problems.