Marine Installation Manual
2022-03
6-14
6 Engine Dynamics
6.3 Longitudinal vibration (pitching)
X62DF-S2.0
6.3
Longitudinal vibration (pitching)
Strong axial vibrations in the shafting, transmitted from the thrust bearing to the
engine structure and foundation, can excite inadmissible longitudinal vibrations
at the engine top and as a consequence in the superstructure (refer to section
). In any case, to prevent such vibrations, the double-bottom structure
should be as stiff as possible in the longitudinal direction.
Reduction of longitudinal vibration (5-cylinder engines)
In general, longitudinal stays are only especially needed on 5-cylinder engines
when a shafting layout has a main torsional critical speed above the nominal
speed, resulting in strong longitudinal engine vibrations at the top of the engine
block. This tends to only occur by using intermediate shafts with oversized diam
-
eters, which is no longer common today.
Longitudinal stays
to prevent vibration
in superstructure
However, there can be installations where it might be beneficial to install longi
-
tudinal stays. This is not because of inadmissible longitudinal vibrations at the
engine top but because of possible disturbing longitudinal vibrations in the super
-
structure, close to nominal speed. By fitting longitudinal stays the disturbing res
-
onance can be shifted above nominal speed.
The decision of whether longitudinal stays are required or not has to be made by
the shipyard based on a global ship vibration investigation, or on vibration meas
-
urements taken at the top of the engine block and in the superstructure (on the
first vessel of a series). They are arranged as shown in
.
Figure 6
-
14 Arrangement of longitudinal stays
Friction type stays
Friction type stays can be installed according to WinGD design, on either the en
-
gine’s free end or driving end side. The layout of WinGD friction type stays,
which is linked to the ‘Engine stays’ drawing for the application of longitudinal
stays, must conform with the specifications. Deviations are not acceptable, espe
-
cially the friction coefficient of the shim and the disc spring properties, which
must follow exact specifications.
NOTE
If longitudinal stays are required, WinGD recommends to install
friction type stays according to WinGD design or alternatively, hy
-
draulic type stays from third-party suppliers.
SM-0211
Driving
End
Free
End
Fuel Side
1
n
OR
