CRITICAL SPEED RANGE

Critical Speed Range (or Barred range)

-is the range of speed at which resonance may occur.

-Resonance is a phenomenon experienced when the engine’s operating frequency coincides with the natural frequency of the hull which results in vibrations of higher amplitudes than normal which is very dangerous.

-The critical speed range should be passed as soon as possible.

-In order to avoid operation of the main engine in critical (or barred) speed range, a quick-pass function is provided.

If the bridge command is within these areas, the lamps for critical rpm limit on the bridge and in the engine control room will illuminate.

The system will,

-during acceleration, keep the engine running below the lower critical speed,

-during deceleration it will keep the engine running above the upper limit.

Indications of Critical speed range :

- More vibrations can be experienced.

- The lamps for critical rpm limit on the bridge and in the ECR will illuminate.

*The speed range is marked RED in all Manoeuvring Panels. (Bridge, ECR, Local)

*The critical speed range is also labeled adjacent to the Manoeuvring Panels or near the telegraphs.

Means to reduce the amplitude of vibrations:

-sectionalizing of the shafting and

-interposing special couplings between sections.

-using vibration absorbers fitted to the crankshaft.

Means to avoid resonance is to adjust:

-speed of the engine

-mass of the flywheel or

-engine’s firing order.