Difficulties During Installation:

• The ship's configuration changes when transitioning from being berthed to afloat, affecting alignment.
• Natural deflection of the shafting occurs between supports due to its length and weight.
• The propeller's weight creates a cantilevered effect on the shaft, further complicating alignment.

Difficulties During Service:

• The ship's loading conditions (cargo, ballast, fuel, and water) affect alignment.
• Movement of the ship in water causes dynamic changes in alignment.
• Off-centre thrust from the propeller can create additional forces on the shafting system.
• Wear down of bearings over time impacts alignment.
• Water forces acting on the vessel's hull cause distortion, affecting shaft alignment.

Reasons for Unreliable Results:

Results are often unreliable due to various external factors such as temperature fluctuations (high deck temperatures in tropical climates versus low sea temperatures), wind, waves, draft, and water density. The ship's hull can distort due to hogging and sagging under different loading conditions, affecting the alignment measurements. Cargo weight and distribution, ballast, fuel, and water levels are all subject to change, further impacting the accuracy of measurements. Over the ship's lifetime, extreme weather conditions can alter the hull's shape, leading to variations in shaft alignment.

• Uneven wear down of bearings.
• Hull deformation caused by hogging, sagging, or prolonged stress.
• Improper or incomplete alignment during initial installation.
• Changes in loading conditions, cargo distribution, and ballast arrangements.
• Long-term effects of extreme weather and sea conditions.
• Propeller thrust misalignment due to incorrect propeller installation or damage.
• Vibration and fatigue in the shaft system.

A simple sketch to illustrate bearing load assessment using the jacking method:

Hydraulic jacks are placed on either side of the bearing and used to lift the shaft. A dial gauge measures the shaft's lift, indicating the amount of force needed to lift it. The hydraulic pressure exerted by the jacks directly corresponds to the load on the bearing. By comparing this load with design specifications, engineers can determine if the load is evenly distributed among bearings.

• Alter the height of the bearing from the tank top by loosening the foundation bolts and tightening the jacking bolts.
• Insert or remove shims between the bearing housing and foundation to achieve proper alignment.
• Compare the actual bearing load with the original load specified in the manual and make adjustments accordingly.
• If the bearing is excessively worn or clearance exceeds limits, replace the bearing to restore proper function.