When a ship’s stern has heavily struck a dock wall, a thorough inspection must be carried out in dry-dock to assess any structural damage and ensure the integrity of propulsion and steering systems.

External Hull Inspection

• The stern frame and surrounding shell plating must be carefully examined for cracks, indentation, or buckling caused by the impact.
• All welded joints, especially at the connection between the stern frame and hull structure, should be checked for fractures or signs of failure.

Rudder and Steering Gear

• The rudder blade should be inspected for distortion, cracks, or surface damage.
• Pintle clearances and jumping clearances must be measured to confirm that the rudder is correctly aligned and properly seated.
• The steering gear system, including hydraulic rams and seals, should be checked for oil leakage or abnormal movement, which may indicate internal misalignment or damage.

Propeller and Shafting System

• The propeller blades must be inspected for bending, cracks, or deformation such as curled tips.
• The stern tube seals or stern bush (whether oil- or water-lubricated) should be examined for leakage or signs of water ingress.
• A shaft run-out test should be conducted to detect any bending or misalignment of the tailshaft.

Internal Inspection

• The steering gear room structure, including foundation bolts and seating arrangements, should be checked for any shifting or structural damage.
• The aft peak tank and adjacent compartments must be inspected for internal damage, cracks, or compromise of watertight integrity.

If the propeller is found to be damaged beyond repair, it must be replaced with a spare propeller. This operation requires precision to ensure proper power transmission and long-term reliability.

Procedure for Propeller Replacement

1. Dismantling the Damaged Propeller: Remove the propeller cap (fairing cone) and unscrew the propeller nut. Use hydraulic equipment such as jacks or Pilgrim nuts to break the interference fit between the propeller boss and the shaft taper.
2. Supporting and Removing the Propeller: Use suitable lifting arrangements, such as chain blocks and slings, to safely support and remove the propeller without causing damage or imbalance.
3. Preparation of Contact Surfaces: Thoroughly clean the shaft taper and the bore of the spare propeller. Both surfaces must be completely free from dirt, grease, or corrosion.
4. Checking Contact (Blue Fit Test): Apply marking compound (e.g., Prussian blue) to the shaft taper and mount the propeller temporarily to check the contact area. At least 70–80% surface contact is required to ensure proper seating.
5. Final Mounting: Using a hydraulic nut (such as a Pilgrim nut), push the propeller onto the shaft taper to the specified push-up distance, as determined by design calculations.
6. Securing the Assembly: Tighten the propeller nut, fit any locking arrangements or keys (if applicable), and reinstall the propeller cap. The cap is usually filled with tallow or a corrosion-inhibiting compound to protect internal surfaces.

Precautions for Correct Assembly

• Surface Cleanliness: The shaft taper and propeller bore must be perfectly clean. Even minor contamination can cause improper seating, leading to stress concentration or misalignment.
• Correct Push-Up and Temperature Consideration: The hydraulic push-up pressure and distance must be accurately controlled, taking into account ambient temperature, as it affects material expansion and interference fit.
• Key and Keyway Inspection (if applicable): Ensure that the key fits properly and does not bottom out in the keyway, as this would prevent full contact between the taper surfaces.
• Proper Sealing: All sealing elements, including O-rings between the propeller boss and shaft and within the propeller cap, must be in good condition to prevent seawater ingress and subsequent corrosion.
• Verification of Propeller Specifications: Confirm that the spare propeller matches the original design in terms of diameter, pitch, and direction of rotation, ensuring compatibility with the propulsion system.