Marine Installation Manual
2022-03
6-20
6 Engine Dynamics
6.6 Whirling vibration
X62DF-S2.0
6.6
Whirling vibration
Whirling vibrations are generated when the shaft rotates and goes into transverse
oscillations. If the shaft is out of balance, the resulting centrifugal forces will in
-
duce the shaft to vibrate. This vibration is commonly known as
whirling vibration
,
bending vibration
or
lateral shaft vibration
.
Whirling vibrations are in most cases not relevant in propulsion shafting with di
-
rectly coupled low-speed 2-stroke engines. Typically, whirling vibrations are
only relevant in 2-stroke installations having a very long shaft line (longer than
60 m).
Many classification societies do not require whirling vibration calculations for
installations with low-speed 2-stroke engines. In general, only the natural
whirling frequencies are calculated. The number and position of the shaft bear
-
ings have a significant influence on the natural frequencies. As such, the whirling
vibration calculation must be performed after or together with the alignment cal
-
culation.
