Longitudinal Vibration

Understanding Vibrations in Marine Engines

Vibrations are an integral part of every mechanically moving component or machine on board ship. Vibrations in marine engines are a result of periodic or random oscillations caused about an equilibrium point.

When these same vibrations occur in machines with bigger size, operating under heavy loads (2-stroke marine propulsion engine) the intensity of vibration levels would magnify because of large mass rotation and combustible gases forces inside the machinery.

If the vibration levels increase beyond the minimal level i.e. when mechanical system has one or more frequency, it may lead to deformation or breakage of engine components. It is therefore important to damp the vibration by some external arrangement.

In a 2 stroke marine propulsion engine there are basically 3 types of vibrations that act on the engine when it is in operating condition:

Longitudinal Vibration

This type of vibration occurs as a result of guide forces resulting from transverse reaction forces on the crossheads. The transverse reaction forces are generated when connecting rod and crankshaft mechanism converts reciprocating motion in to rotary motion. Such vibrations move the engine top athwart ship causing rocking or twisting.

Axial Vibration

Axial vibration is a kind of longitudinal shafting vibration which occurs in the crankshaft because of the radial as well as tangential forces.

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