US Patent 7794296 Method to assemble marine drive system, and marine propulsion apparatus

A method to assemble a marine drive system wherein an acceptable-unacceptable criterion on the torsional vibration of a shaft of the marine drive system is established based on the correlation between the torsional stiffness of a propeller shaft and the moment of inertia of a propeller. A desirable elastic coupling for the marine drive shaft is selected based on the criterion. The marine drive system is assembled by using a flywheel, a marine reverse and reduction gear, and an elastic coupling, whose property is changeable, lying between an input shaft of the marine reverse and reduction gear and the flywheel.