Marine Shaft Refurbishment and Drivetrain Overhaul During Dry Dock Support

When a Scottish cruise ship ran aground, the impact sheared the output shaft on the starboard ZF 2250 gearbox and damaged the starboard propeller, taking the propulsion system out of service. MIT were called in to lead the repair programme, managing a full drivetrain overhaul from initial removal through to final laser alignment and handover. The project encompassed gearbox removal and overhaul, marine shaft inspection and refurbishment, propeller and rudder repairs, coupling replacement, and complete reinstallation of the drivetrain system.

This work formed part of a wider dry docking programme. Dry dock conditions allow for the precise inspection, repair, and reassembly required to restore full drivetrain integrity. For operators, a structured propulsion overhaul of this kind reduces the risk of secondary failures and returns the vessel to service with confidence.

Project Overview: Marine Drivetrain and Propulsion Refurbishment

• Remove port and starboard ZF 2250 gearboxes for overhaul
• Remove rudders and propellers
• Remove starboard companion coupling
• Check run-out of port and starboard prop shafts
• Reinstall all components, including rudders, propellers, prop shafts, couplings, and gearboxes
• Laser alignment of starboard and port gearbox, including moving the engine to ensure correct alignment

Client:

Technical Managers of a small passenger vessel

Location:

Belfast, Northern Ireland

The Technical Scope: Gearbox and Marine Shaft Removal

MIT were initially contacted to assist with the removal and overhaul of the starboard ZF 2250 gearbox following grounding damage. Through discussion with the technical management company, the full extent of the required work became clear: both the port and starboard ZF 2250 gearboxes required removal for overhaul, and the port and starboard propellers and rudders had sustained damage requiring repair and class approval.

Before work commenced, MIT’s Marine Sales Engineer worked through the scope in detail with the technical managers to confirm the full extent of works and plan the removal sequence. Upon attending the vessel, the engineer used the vessel plan to identify the lifting eyes and determine the removal route for both gearboxes. The gearboxes were drained, and electrics, hoses, and ancillary components were disconnected. Both the port and starboard ZF 2250 gearboxes were then removed and palletised along with their associated components for uplift.

In harsh marine operating environments, drivetrain components are subject to a combination of sustained load, shock loading, vibration, and environmental exposure. It is this combination of factors, not any single cause, that drives wear and fatigue in propulsion systems over time. Planned lifecycle maintenance during dry dock periods is the most effective way to manage this, allowing for thorough inspection and intervention before cumulative wear leads to failure.

Assessing the Refurbishment of Marine Shaft Straightness and Run-out

While the propellers and rudders were being removed, the team carried out a run-out check on the port and starboard prop shafts, both inboard and outboard. The measured run-out was off by 0.28mm, which placed it outside tolerance and meant the affected prop shaft had to be removed for further investigation and lathed back to specification.

This decision point, whether a shaft can be corrected on the lathe or requires replacement, is a critical stage in any marine shaft refurbishment. Precise measurement at this stage directly informs the scope of remedial work and ensures that the reinstalled drivetrain meets the tolerances required for reliable service.

Replacing the Damaged Marine Shaft Couplings

The grounding damage that sheared the tailshaft also caused damage to the starboard inboard companion coupling. Once the shaft issue was confirmed and the prop shaft removed, the damaged coupling was extracted and replaced with a new unit upon the shaft’s return. Shaft couplings must be assessed carefully during any drivetrain overhaul. Even minor damage to a coupling can compromise alignment and transmit damaging loads through the gearbox and shafting.

Marine Shaft Seal Maintenance and Propeller Refurbishment

The port and starboard prop shaft seal box gland packing was removed as part of this phase, with new packing installed during reinstallation to prevent ingress and leakage once the vessel returned to service.

In parallel, our approved partners carried out the propeller and rudder refurbishment:

• Propellers:  All blades repaired and balance-tested.
• Rudders:  Repaired and surveyed to confirm class compliance.
• Seal box gland packing: Renewed on both port and starboard shafts.

Class approval and balance testing are not optional steps. They are essential to confirm that repaired rotating components meet the standards required for safe and efficient operation. Unbalanced propeller blades generate vibration that propagates through the shafting, couplings, and gearbox, accelerating wear across the entire drivetrain.

Precision Reinstallation of the Coupling, Shaft and Propeller Assembly

With overhauls and repairs complete, MIT returned to the vessel to refit the full propulsion assembly in sequence: tailshaft, new starboard inboard companion coupling, seal box gland packing, propellers, rudders, and the overhauled port and starboard ZF 2250 gearboxes. Reinstalling in the correct sequence allows each component to be correctly positioned and verified before the next is fitted, which is essential for achieving accurate final alignment.

Laser Alignment and Engine Positioning for Optimal Performance

Alignment checks during reinstallation revealed a significant discrepancy between the two sides:

Port Side: Within tolerance.

Starboard Side: Massively out of alignment.

Correct driveline alignment is fundamental. Misalignment places abnormal loads on gear teeth, shaft bearings, and couplings, accelerating wear and increasing the risk of premature failure across all connected components. It cannot be underestimated. To correct the starboard alignment, the engines were lifted and the engine mounts removed and machined, allowing the engine and gearbox to be repositioned by the required amount. Once the correct alignment was achieved, both gearboxes were tested to confirm proper operation and readiness for return to service.

Conclusion: Restoring Operational Readiness with Expert Marine Shaft Services

This project demonstrates the value of a structured, systematic approach to drivetrain overhaul following grounding damage. By combining ZF 2250 gearbox removal and overhaul, inboard and outboard prop shaft inspection and lathing, companion coupling replacement, seal box gland packing renewal, class-approved propeller and rudder refurbishment, and precision laser alignment, MIT was able to restore the vessel to full operational readiness from a condition of significant drivetrain damage.

The starboard alignment finding during reinstallation underlines why thorough verification at every stage matters: a drivetrain that appears repaired but leaves dry dock out of alignment will present the same failure risk that brought the vessel in. Complete, correctly sequenced overhaul is what delivers a reliable return to service.

Concerned About Drivetrain Downtime During Dry Docking? Contact Our Marine Team Today

If your vessel is approaching a scheduled dry dock period or has sustained propulsion damage, MIT’s marine engineering team can support you from initial scope through to final alignment and handover.

Contact us today to discuss your requirements.