2.3.1 Where
the design of gearing has used enhanced analysis methods as described
in Vol 2, Pt 3, Ch 1, 2.3 Enhanced analysis principles 2.3.2 to Vol 2, Pt 3, Ch 1, 2.3 Enhanced analysis principles 2.3.5, the ship will be eligible
for the optional machinery class notation AG1 or AG2 as
applicable. These optional class notations may be applied where the
Owner requires detailed knowledge of the reliability of the gear elements
and where noise excitation is required to be minimised for anticipated
service conditions. Eligibility for the AG1 class notation
will be subject to analysis in accordance with ISO 6336 and the use
of an acceptable validated analytical meshing model for determining
the face load factor for contact stress K
Hβ by
direct calculations. The analytical mesh model is to include consideration
of the following:
-
Phase varying
lines of contact at the mesh.
-
Elastic deflection
of the gears, supporting shafts and other supporting components.
-
Geometric qualities
of any helix and profile modifications.
-
Manufacturing
tolerances.
2.3.2 Where,
in addition to the requirements for AG1 class notation,
a validated three dimensional finite element program is used for determining
the flexibility of the geometry of mating gears, the ship will be
eligible for AG2 class notation.
2.3.3 Gear
elements are to be analysed using ISO 6336 with the following additions:
-
The face load
factor for contact stress (K
Hmesh) is to be
calculated using an acceptable validated analytical meshing model
and used in place of the equivalent factor (K
Hβ x K
Hα) given in ISO 6336. The actual factor
of safety against surface failure is effectively adjusted as follows:
-
The face load
factor for bending stress (K
Fmesh) is to be
calculated in accordance with ISO 6336 using the K
Hmesh value calculated from the validated analytical mesh model.
The actual factor of safety against surface failure is effectively
adjusted as follows:
The factors of safety derived from the stress analysis procedure
are only to be used for comparing the gears of similar design.
2.3.4 The
ability of gearing to operate without scuffing at loads up to and
including the maximum specified transient overload is to be demonstrated
using at least two different methods. The assessment is to take full
account of predicted transverse load distribution.
2.3.5 The
design of the gearing is to be capable of accepting the following
overload conditions as applicable and the over-speed without risk
of damage:
-
A non-transient
ahead torque overload (duration of more than three seconds) of 125
per cent maximum full power torque in steam turbine and diesel installations,
and of 150 per cent maximum full power torque in gas turbine installations.
Torque levels up to these may occur during high power turns and rapid
accelerations up to a total of five hours during a ship's life. Gears
and shafts are to be capable of withstanding 200 per cent of full
power statically as could occur if for instance the propeller becomes
jammed.
-
Over-speed of
15 per cent above the specified input speed.