Effects of Continuous Running at Service Speed in Heavy Weather

When a ship operates continuously in heavy weather, the propeller experiences irregular immersion, racing, and vibration due to pitching, rolling, and slamming. These fluctuating forces are transmitted through the propeller shaft, intermediate shaft, and main engine, resulting in:

• Fluctuating torsional and bending stresses
• Overheating and fatigue of rotating machinery
• Misalignment and loosening of mountings
• Excessive wear on bearings and couplings

Hence, after prolonged operation in such conditions, thorough inspection and maintenance of all shafting components are essential.

(a) Intermediate Shafting

Effects:

• Bending stresses due to hull deflection and resulting misalignment.
• Possible scoring or overheating of bearings.
• Increased vibration and fretting at coupling ends.

Checks / Maintenance:

• Check bearing alignment using jack-up tests or dial indicators.
• Inspect bearings for signs of overheating, scoring, or oil film breakdown.
• Examine the shaft for run-out and ensure all coupling bolts are tight.

(b) Tail Shafting

Effects:

• Excessive vibration and whipping caused by propeller racing.
• Sea water ingress through stern tube seals due to fluctuating loads.
• Possible wear of aft bearing due to misalignment or loss of lubrication.

Checks / Maintenance:

• Check stern tube oil for contamination (water or metal particles).
• Inspect stern tube seals and ensure adequate lubrication.
• Measure bearing clearances and check tail shaft deflection if required.

(c) Shafting Coupling Bolts

Effects:

• Alternating torsional stresses may cause loosening, fretting, or even shearing of bolts.
• Loss of pre-load may result in slippage between coupling faces.

Checks / Maintenance:

• Check tightness and torque of all coupling bolts.
• Inspect bolts and bolt holes for fretting marks or elongation.
• Examine coupling flanges for surface damage or distortion.
• Replace any stretched or damaged bolts, tightening new ones with calibrated torque tools.

(d) Engine Supports

Effects:

• Engine bedplates and chocks are stressed by dynamic hull deflections and vibration.
• Possible loosening of holding-down bolts or settlement of chocks.
• Resultant misalignment between engine and shaft line.

Checks / Maintenance:

• Check tightness of all holding-down bolts and inspect for cracks around seating areas.
• Verify chock integrity, especially for resin chocks, and check alignment.
• Inspect for oil leaks or corrosion at bedplate interfaces.

(e) Thrust Pads

Effects:

• Fluctuating propeller thrust due to racing and slamming causes uneven loading.
• Oil film breakdown can lead to wear, scoring, or overheating.
• Possible edge loading due to misalignment.

Checks / Maintenance:

• Inspect thrust bearing pads for scoring, pitting, or discoloration (indicating overheating).
• Check bearing clearance, oil supply pressure, and temperature.
• Verify alignment and check the thrust collar for surface damage or wear.