DNV, together with Daewoo Shipbuilding and Marine Engineering and MAN B&W, has successfully carried out a R&D project on the effect of hull flexibility on shaft alignment. The aim of the project was to close the gap between analysis of shaft alignment and real life shaft alignment by increasing the knowledge of several critical design parameters.
Shaft alignment has been a hot issue for some time. There seems to be an increasing trend of damage caused by shaft misalignment. Typical outcomes of shaft misalignment are breakdown of bearings in sterntube and engine. Such damage can be of great consequence since it involves costly repairs and its cause is often difficult to identify.
Mounting of a shafting system has to be carried out accurately. Typical tolerances are only 0.1mm, even on shaft diameters up to 1,000mm. Often there is a conflict regarding acceptance criteria to be followed in the installation procedure. These conflicts make it impossible to fulfil all the acceptance criteria within the required tolerance.
The conflicts arise because the alignment model is a simplification of the physical installation. There are several parameters that, at present, are not considered in the analysis. This situation, with strict acceptance criteria combined with unknown important physical parameters, is not satisfactory.
The research project has aimed to increase knowledge of critical parameters, such as draft, tank fillings and thermal loads. This was accomplished by combining measurements and analysis for a VLCC. The final report is being completed presently and the results will be published during next year.
For more information contact:
Geir.Dahler@dnv.com