eng Science and Education Publishing Journal of Mechanical Design and Vibration 2376-9572 2017-09-27 5 1 37 42 10.12691/jmdv-5-1-5 JMDV2017515 article Jabbar Firouzi 1 Hassan Ghassemi gasemi@aut.ac.ir 1 Department of Maritime Engineering, Amirkabir University of Technology, Tehran, Iran Finding the whirling speed of the shaft of the ship propeller is presented on this paper. Power generated from the engine is transmitted to the propeller directly/indirectly using gearbox. This is important to find the natural frequencies of the shafting system in order to prevent resonance. So, multi-DOF (degree of freedom) is considered on this study including engine, gearbox and propeller, flywheel and etc. connecting by the shaft. Whiling speeds of the shaft are determined at various conditions as well as the effect of the shaft torsional stiffness and shaft diameter are presented and discussed. http://pubs.sciepub.com/jmdv/5/1/5/jmdv-5-1-5.pdf propeller shaft whirling speed torsional vibration