Investigation on effective support point of single stern tube bearing for marine propulsion shaft alignment

Over the last few decades, oil tankers and bulk carriers, which preferably adopting the concept of a single stern tube bearing, have been subjected to the mechanical damages on propulsion shaft bearings since such a concept overly requires a single bearing to support the full load of the propulsion shaft. This paper was to fundamentally address the problem of current practices of aligning a single stem tube bearing for commercial ships by determining the effective supporting point to balance the load of the propulsion shaft properly. Since selecting a case ship subjected to the damage on the stem tube bearing, it investigated the actual cause of the damage, thereby finding a practical way to enhance the sustainability of the propulsion shaft system using the single stem tube bearing. Computer-aided simulations using the finite element analysis as well as on-site measurements were carried out. Research findings revealed that the ignorance of the relative slope angle between the propulsion shaft and the aft stem tube bearing had led to misalignment, which resulted in adverse effects on the stability of the shaft system, and consequently damaged the stem tube bearing. Results of the analysis suggested that the degree of slope be taken into account when estimating the effective supporting point of the bearing. Finally, this paper pointed out that the establishment of a shaft installation guideline considering the effect of the shaft slope, thereby preventing wiping damage of the aft stem tube bearing would be an urgent task.