international classification society Bureau Veritas has introduced a new set of
requirements for shaft alignment on high powered ships. The ESA notation will
help ensure the integrity of the structure and shaft bearings on very large
vessels such as ultra-large container ships and the next generation of very
large LNG carriers.
Segretain, deputy technical director, Bureau Veritas, says, “As ships grow in
size and we seek more fuel economies we are now seeing vessels with shafts
handling over 20MW of power driving large diameter propellers of over 30 tonnes
weight. Critical attention has to be paid at the design stage to analysing the elastic
shaft alignment and ensuring that the bearings and structure match the shaft
response, especially when the vessel is turning. If this is not done, huge
forces will either lead to bearing failure or excessive vibration. We have been
called in to help solve incidences of both on new ships. This new ESA notation
sets out standards of how the shaft must be analysed and the criteria the whole
shaft, bearings, and aft structure must meet to avoid such problems.”
Veritas has unrivalled experience with shaft alignment studies dating back to
the first ULCCs built in the 1970s. It is continually updating its expertise in
this area and has developed special software for shaft analysis.
Elastic Shaft Alignment (ESA) notation will apply to vessels with shafts in
excess of 750 mm diameter, or smaller shafts handling over 20 MW of power,
propellers over 30 tonnes or using synthetic bearings. The notation requires
full analysis of the criteria covering hull flexibility with respect to loading
conditions, bearing material stiffness, shaft speed and oil film behaviour.
Segretain, “We will make this notation obligatory for ships meeting these
conditions in our class, and will also make it available as a voluntary
notation for smaller vessels and vessels not in BV class. Getting the
shaft/structure right is critical for modern designs and we have the deepest
expertise in this area available anywhere. This notation helps to codify that
and guide yards with new designs.”
a graphic to illustrate shaft alignment e mail firstname.lastname@example.org
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Labels: classification, containerships, propellers