Examples of technical solutions to machinery alignment problems. Discussion

This paper describes a case in which telescope readings were used, in conjunction with strain gauge measurements, to obtain the alignment and correct boring instructions for the tail shaft bearings relative to the rest of the propulsion machinery. Thus, only the tail shaft bearings needed to be adjusted to obtain a satisfactory alignment. The final alignment of the assembled shaft was checked with strain gauges. The technique is very accurate and it is demonstrated that it is to a great extent self-checking. The problems with a ship which suffered bent intermediate shafts are also described. The effects of a bent shaft on the alignment measurements are first discussed generally. Various measurements, which were carried out in order to be able to advise the shipyard on the advisability of operating the ship with the bent shaft, are then described. The torsional vibrations of the installation were then measured as it was suspected that these vibrations released the internal stresses in the shaft, thus causing it to bend. The forging procedures were studied and the internal stresses measured by a specialist company. It was finally concluded that the release of the internal stresses was the cause of the shaft bending.