The propulsion shafting not necessarily has to be aligned along a straight line.  In other words, if one draws a line between the tailshaft aft cone centre towards the centre of the M.E. crankshaft or, the L.S. gear centre, if a reduction box is installed, the optimum shafting, in most cases, has to snake along that line.  The best elastic curve of the lineshaft is determined using the hydraulic jacking method and offsetting the bearings in a trial and error manner.