Alignment of bearing journals in relation to stern tube
A laser beam can be used for stern tubes and bearing journals, when the shaft is removed, along the centre line. This is what we call bore alignment. An example of a measurement system used for this is Easy-Laser E950. Because the measurement is performed in the centre of the bearing, the instruments are suitable for shafts of both small and large diameters. The measurement method is based on a laser transmitter being mounted on the axial surface at one end of the stern tube (or on the gearbox flange or in the final support bearing) and the detector unit being placed in the bearing journal. Measurement values are recorded at a distance in the bearing sleeve as shown in the drawing. The measurement program makes calculations and then shows the position in the vertical and horizontal axes as well as first and second "slope" if necessary. As adjustment is performed on land or in the dock, if required compensation values can be entered to correspond with the position of the bearings when the vessel is in the water.
If necessary, the roundness of the bearing can also be checked. This is best performed using a bracket with a measurement probe, see image.
Easy-Laser can be used to measure bearing play: mount one measuring unit on the shaft and the other to a fixed part of the machinery. Then raise the shaft (with an aid) and read off any play.
On water jet drive systems, it may be desirable to align to a mounting flange (i.e., a surface perpendicular to the centre line of the shaft). A laser transmitter with integrated angular prism is then needed, e.g. Easy-Laser D25.