Effect of Free Rotation Period of Propulsion Shafting and Stopping Efficiency

Through the past studies, it has been pointed out that the duration of free rotating period of propulsion shafting system may affect the stopping ability of the ships. However, in the studies of predicting stopping ability of the ships, more specifically in the predicting stopping distances of the ships, it is a common practice to treat the free rotating period as a certain fixed length of time, or to neglect as it is short. It may be one of the reasons why current simplified and practical predicting methods of stopping ability sometimes show greater deviations between the prediction and the actual result. In order to solve such problems, at this time, the duration of free rotating period have been assessed for actual data of the ships with diesel main propulsion engines to grasp current situation, the scenario of free rotating of propulsion shafting system has been considered, and based on which how the free rotating period affects the stopping ability has been considered. In addition, possible predicting method taking essential feature of free rotating of propulsion shafting system into account based on practical and reasonable approximation has been considered, using which trail calculations have been carried out on the sample data of 132 vessels. Deviations between predictions and actual results have been improved compared with conventional method.