A cargo vessel propulsion system torsional vibration calculation has been delivered to our customer! Some of the data was not provided by the manufacturer, but experienced IMT team filled the gaps by the statistical data and additional preliminary calculations. The standard Class recommendation for torsional vibratory loads from 3-blade propeller was too big for this small-speed vessel to meet the requirements. That’s why we performed detailed calculation based on the lifting-line theory taking into account the exact blade geometry and wakefield from our library for the similar ship. The results were 6 times less and after that corrections, all acceptance criteria met the requirements of the Class and equipment manufacturers with a reasonable margin. The ShaftDesigner software provided all capabilities to perform this calculation and to prepare the final report as quickly as possible.