Somewhere in Scandinavian waters there is a very fast and
manoeuvrable "stealth" patrol boat powered by two 1 mega watt gas turbine water
jet propulsion units.
The power from the very high revving turbines is delivered to the
water jet impellors through gearboxes manufactured by Allen Gears.
Bennett Associates was engaged by Allen Gears to analyse the
gearbox casings, from the analysis determine the misalignments within the
gearbox and to design aluminium frame structures that fit within the fibreglass
hull to support the gearbox, gas turbine and all the ancillary acoustic
shrouding. The gas turbines are mounted directly on to gearboxes and the
complete unit mounted on springs.
Part of Bennett Associates' contract was to verify that the design
met DNV regulations, which covered the shock impulse load criteria. When the 6g
as defined by DNV regulations was applied it actually generated a 12g impulse to
the equipment on the frame.
The initial work carried out by Bennett Associates to resolve the
acceleration issues also predicted problems with the way that it was proposed to
mount the turbines. The interface between the gas turbine running at very high
RPM and the gearbox is particularly complicated. Care had to be taken not to
inflict extraneous loads on to the turbine.
Bennett Associates went on to liaise with all the parties to
resolve the turbine mounting problems, validate that the whole of the propulsion
package met the DNV criteria and to ensure that the units fit the tight confines
of the vessel.
The design was finalised using detailed FE models. The vessel
has been in service for a number of years and to date there has been no reported
problems with the propulsion units.
For more information, contact us on
01709-373782
M G Bennett and Associates Ltd is now part of the  Group
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