Common sense suggests that the bearings supporting marine propulsion shafting be aligned so they hold the shaft in a straight line, since offsetting one bearing with respect to another would bend the shaft. Moreover, industrial machinery is typically aligned so that the shafts of the driving and driven machines are collinear [1]. However, this approach is not always appropriate for marine main propulsion shafting because:
a) its bearings move as conditions change, and b) the shafting is never really straight because it deflects under its own weight and the weight of the propeller and other attached components.
Therefore, the vertical and athwartships position of the bearings must be aligned so that the limits established to ensure proper system operation are not exceeded for all normal ship operating conditions. It follows that shaft alignment could also be called bearing alignment since the alignment is a direct result of the position of bearings that support the shafts. Ship operators surveyed by SNAME, as well as the US Coast Guard and the US Navy, expressed a need for a technical reference guide on the alignment of main propulsion shafting.
This document is intended to provide these guidelines for personnel involved in the design, installation, and operation of marine propulsion shaft lines. This guide provides a general overview of shaft alignment for the novice and more detailed information for the person with some knowledge on one facet of shaft alignment that needs more information on another alignment topic. Ship operators surveyed by SNAME, as well as the US Coast Guard and the US Navy, expressed a need for a technical reference guide on the alignment of main propulsion shafting. This document is intended to provide these guidelines for personnel involved in the design, installation, and operation of marine propulsion shaft lines. This guide provides a general overview of shaft alignment for the novice and more detailed information for the person with some knowledge on one facet of shaft alignment that needs more information on another alignment topic.