Application of the stiffness method to the optimization analysis of a marine propulsion shaft system

Reliable calculation of bearings reaction of marine propulsion shaft is one of the most important tasks in the project and maintenance of a propulsion system. This can prevent damages and failures on the propulsion components and also extend its lifetime. The marine propulsion shaft system, beyond a mechanical element responsible for transmitting torque and power, is also a structure subject to its mechanical characteristics and loads. Therefore, as a structure, it must be analyzed as long as the resulting loads on all supports, bending moments distribution, inclinations, deflections and shear forces are known in operational conditions. Some optimization process must be applied to the structure, starting from its static analysis, to guarantee that all supports are sustaining load. This is one of a few criteria that must be checked and that must be satisfied so that the propulsion shaft system may operate safely and free from mechanical problems. This paper describes the application of a structural matrix analysis calculation method known as "stiffness method" to the analysis of the propulsion shaft system. A stiffness method framework developed by one of the authors is presented and used to analyze the propulsion shaft modeled as a beam. The propulsion shaft system from an Anchor Handling Tug Supply vessel is used as a case study and the results are compared with the finite element method. The stiffness method features great reliability achieving an average bearing load difference of 6.9% to the finite element method.