The influence of shaft line alignment accuracy on the operational reliability of marine propulsion systems

The paper presents a method of identification parameters of shaft line alignment and its influence on operational reliability of marine propulsion system. The discussion about shaft line parameters (bearings' reactions, bending moment and shear forces acting on crankshaft or gear box, and stresses distribution in the shaft line) which has an influence on marine propulsion system reliability was presented. Proper shaft line alignment is often a problem for repair shipyards, for aged ships without sufficient documentation. Some data can be draw by measurements; e.g. shaft line dimensions or intermediate bearings' reactions. Other data (stern tube bearing load, real axis of shaft line) have to be determined on the base of calculations. Author proposed combined experimental-analytical method for identified and optimization (correction) some existing parameters and checking power transmission system’s foundation. Specialised software (based on Finite Element Method) has been developed for shaft line alignment calculations. Main novelties of the software are elastic supports (model of bearings – boundary conditions) of the shaft line, continuous support as a model of stern tube bearing and influence coefficients calculations. An example analysis with discussion has been performed for cargo ships with medium-speed main engine. Multi-variant computations supported by measurements of the ships’ shaft line have been carried out. Changes in shaft line alignment have been proposed in order to increase reliability of propulsion system.