Question

a) State four operational conditions that may lead to vibration of main transmission shafting.

b) Suggest methods to reduce the vibration levels that occur in main transmission shafting.

ANS

a) Four operational circumstances that may lead to vibration of main transmission shafting are;

Main engine running through it's critical speed range.

Damaged propeller or propeller cavitation.

The ship being in ballast condition, blades cutting the surface.

Shaft turning above maximum revolutions, axial vibration.

b) Methods to reduce the vibration levels in main transmission shafting are;

Where a four bladed propeller is used and causing vibration, it can be changed for a five blade propeller to give less vibration, giving less vibration.

Tortional vibration dampers can be fitted, these dissipate energy given to the system by exciting forces. Also axial vibration dampers can be fitted.

Flexible couplings can be used to give less vibration.

Keeping shaft revolutions with designed limits will prevent excessive vibration.