The Influence of Propeller Mean Loads on Propulsion Shaft Alignment

Shafting alignment in the vertical and horizontal planes is known to be affected by the steady forces and moments generated by the propeller when it rotates. A review is first given of the scant literature on the problem. The origin of the propeller loads is then discussed and it is shown how they can be predicted on the basis of unsteady lifting surface theory. Calculations and some model measurements of steady lateral loads for eight shaft systems are then presented. The effect of each of the six load components on shaft alignment is discussed in some detail. Results are presented from a study based on mathematical optimization techniques in which propeller loads were included systematically in the shaft alignment selection phase. Recommendations are given for needed research that should aid in avoiding alignment-related failures.