Analysis of the Influence of the Centroid Distribution of the Raft on the Shafting Alignment

Aiming at the problem of shaft alignment disturbed by the centroid distribution of the raft in the ship propulsion system, the quantitative influence of centroid offset on bearing load distribution and axis deformation is revealed. Based on the theory of an elastically supported continuous beam, the finite element model of the raft-shaft coupling system is established. By adjusting the position of the raft counterweight mass point (longitudinal offset range ±0.5 m) to simulate the centroid change, the static solution algorithm is used to analyze the key parameters, such as bearing load and axis alignment accuracy, under multiple groups of centroid offset conditions. It is concluded that when the centroid of the raft moves to the propeller end, the load of the 1# and 2# bearing near the propeller end increases, and the load of the 3# and 6# bearing near the thrust plate end decreases. The lateral offset of the center of mass increases, the axial offset at the stern bearing increases, the maximum deflection of the shafting increases, and the deformation of the raft structure increases. The centroid distribution of the raft is a disturbance source of the shafting alignment state, and its offset will reconstruct the bearing load distribution and cause the axis deformation. It is recommended to control the lateral offset of the center of mass at the design stage and reserve the dynamic compensation margin for the shafting alignment.