As aft stern tube bearing
damages were reported quite often over the past years, which may pose threats to the safe operation of the
ships in the worst cases, shaft alignment has become a more heated topic than
ever before in the
industry. Root cause behind the damages is of interest to all parties involved.
In this regard, concerns have been paid to the “uncertainties” in the shaft
alignment process i.e. from the early shaft alignment design to final execution
of shaft alignment onboard and their contributions to the damage are discussed
as well in the paper. The uncertainties emphasized in the paper as sensitive
and crucial to the shaft alignment behavior are, to the best practice and
knowledge of CCS, identified and elaborated in a practical and effective way. The
uncertainties are mainly focused on: -the propeller hydrodynamic loads -alignment procedures for one stern tube bearing arrangement shafting -instability of viscosity of EALs (Environmentally acceptable
lubricants) against pressure
It is noted it is rather difficult
to get some uncertainties quantified precisely even with advanced computer
programs for the time being. One of the
best solutions to cope with the uncertainties is to improve the safety margin
in the early design stage by
reducing the mismatch angle between bearing surface and shaft. With the above in mind, a robust design of aft stern tube bearing,
e.g. optimized double slope bearing, as a countermeasure is presented in the late part of
the paper.
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