The shafting is the core of a vessel’s propulsion system, connecting the main engine to the propeller and transmitting thousands of kilowatts of power. The accuracy of shafting installation directly determines the vessel’s vibration, noise and bearing life. Jiangsu Haizhongzhou Shipping Industry Co., Ltd. has established a full‑process precision control system for shafting installation, from stern tube boring and bearing pressing to shaft alignment.
The first step of shafting installation is stern tube boring. The stern tube is a cast steel component that is welded and fixed to the hull after block assembly. Due to welding distortion, the centreline of the stern tube bore will deviate from the theoretical position. Haizhongzhou uses on‑site boring equipment to finish the stern tube. The boring bar is supported at both ends by bearing blocks, and the centreline of the boring bar is aligned with the hull baseline using a laser alignment instrument. During boring, the operator monitors the deflection and thermal deformation of the boring bar in real time and makes compensatory cuts when necessary. After boring is completed, the roundness of the stern tube bore is controlled within 0.05 mm, and the centreline deviation does not exceed 0.1 mm.
After the stern tube boring is accepted, bearing pressing follows. The aft bearing and forward bearing are typically made of white metal or polymer material, installed by press‑fitting or freeze‑fitting. Haizhongzhou digitally records the bearing pressing process, plotting the relationship curve between pressing force and pressing distance. If the curve shows abnormal fluctuations, it indicates possible scoring or foreign matter between the bearing and the bore wall, requiring removal and inspection. After the bearing is pressed into place, the bearing inner diameter is measured with an inside micrometer to confirm that the ovality and taper meet the requirements.
Shaft alignment is the soul of the entire installation process. Haizhongzhou uses the “rational alignment method”, no longer pursuing absolute straight‑line alignment, but rather calculating the load distribution on each bearing so that the bearing loads remain within permissible limits under conditions such as hull deformation and temperature changes. During alignment, a laser alignment instrument or optical telescope is used to measure the offset and deflection of the flanges of the intermediate shaft and tail shaft. Haizhongzhou’s alignment standards are stricter than the rules: offset not exceeding 0.05 mm, and deflection not exceeding 0.05 mm per metre. After alignment, the hydraulic jack method is used to measure the actual load on each bearing, requiring the load distribution deviation to be within fifteen percent of the design value.
The tightening of shaft coupling bolts is equally critical. Haizhongzhou uses hydraulic tensioners to apply preload to the bolts, with the tightening sequence strictly following a diagonal pattern in three stages – fifty percent, eighty percent, one hundred percent. The final preload is verified by measuring bolt elongation, with an error not exceeding five percent. After shafting installation is completed, a turning check is performed, requiring a smooth turning torque without sudden changes, and the shafting rotating freely. It is this full-process control from boring to alignment that ensures the long‑term reliable operation of the shafting on vessels built by Haizhongzhou.
