Local Alignment Of Aft Stern Tube Bearing Working On Propulsion Shaft Alignment

Ship’s propulsion system provides the power to the vessel and ensures the safety of navigation.During ship’s new construction stage,for optimised shaft alignment calculation and design,the vertical and horizontal position of bearings were adjusted to fulfil the requirement of statistic bearing load within design margin.It ensures the reliability of propulsion system during its service life.All the bearings except stern tube bearing could be directly measured by bearing jack-up method,also the contact inspection for shaft journal and bearing for aft stern bearing cannot be accessed,so it’s final condition only can assess indirectly.The stern tube bearing failures were happened frequently during recent years.It was not always damaged due to the total loads exceeding the capacity of the bush but for the local loads or edge loads which caused the collapse of lubrication during extreme condition,such as rough sea condition or hard rudder angles in full load condition.Therefore,The local loads distribution along aft stern tube bearing(local alignment)working on propulsion shaft alignment has been studied herein.Based on verification calculation for propulsion shaft alignment and installation,measuring and adjustment of shaft system on site,the local loads distribution along aft stern tube bearing(local alignment)has been calculated and studied.Focusing on two different types of shaft system,the whole installation and alignment processes including bearing load jack-up have been monitored.According the measured data,verification calculation has been carried out for analysis of local alignment of stern tube aft bush.Through this,the more reasonable plan for adjusting and measuring of bearing load has been set up,it provided the more accurate data for optimise design.The changing of bearing loads to the different ship’s draft conditions has been achieved for verification of the assumed boundary condition used for shaft alignment calculation,comparing different calculations in different boundary,the more reasonable one is chosen for further calculation,then the re-cycled calculation repeated as improved cylindrical spiral,the ration range of bearing load of fore stern tube bearing and/or intermediate shaft bearing confirmed to ensure all bearing loads within their design range in different ship working conditions.In this studying,the main changed boundary was the position of supporting points and its quantity of the stern tube aft bearing;author was not only working on the bearing loads on fixed single position but also for loads distribution along the bush with changeable supportpoints against multi-support points while varying the loads of the fore stern tube bearing or intermediation shaft bearing;furthermore,the calculations of bearing loads and bearing influence number for mentioned conditions have been carried out;through the measured bearing loads and jack-up rates,one of those optimized shaft alignment calculations has been selected depending on their different boundary assumption.The tendency of local alignment has been assessed according to hull deflection and changing of the bearing height.Due to present jack-up method for bearing load measurement used on board shops along national and civil shipyards,the processes of machining,installation,measuring and adjustment were monitored.The key points for aft stern bearing relative height and slope were worked out and analysed comparing different type of shaft styles and different installation processes,the affecting factors for installation and measuring have been studied and analysed.The local alignment on aft stern tube bearing were analysed according to the actual measured data;verification calculation and analysis were carried out,and tendency of bearing load to its support points were monitored;the rational range of bearing load has been confirmed in more different ship conditions of the leading vessel.the tendency of bearing load and optimised bearing load range were fed back for further optimise design purpose and adjustment for the sister vessels;the accuracy of bearing loads and optimised bearing loads range were benefit for stern tube bearing local alignment and fulfil the requirement of design to ensure the safety of propulsion system;all the ships’ propulsion system working in a good condition during sea trial,and the measured bearing loads found in accordance with leading vessel.