Aft end vibrations after undocking

Propeller & Hydrodynamics

• Propeller damage from tug contact or unberthing impact.

• Foreign object (rope/wire) wrapped around the propeller or rope guard.

• Imbalance caused by uncalibrated blade polishing or repair work.

• Severe cavitation due to poor hull surface cleaning or damaged rope guard.

Shaft Alignment

• Shaft misalignment resulting from taking gap/sag measurements in dock without re-verifying afloat.

• Incorrect elevation of intermediate shaft bearings.

• Thermal expansion or hull structural flexure differences between drydock blocks and floating condition.

Rudder & Steering

• Excessive rudder pintle or gudgeon clearance after overhaul.

• Loose rudder palm bolts or misaligned rudder blade causing flow asymmetry.

• Air trapped in steering gear hydraulics causing rudder flutter.

Engine & Hull Structure

• Loose main engine holding-down bolts or improperly adjusted top bracings.

• Resonance between Blade Passing Frequency (RPM x No. of Blades / 60) and light-draft hull structural frequency.