Marine Installation Manual 2021-08 6-16
6 Engine Dynamics
6.6 Whirling vibration
X72DF
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.
Alignment Guidelines for Layout Calculation
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