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Propeller Shaft Replacement and DNV Approved Rudder Horn Repair while Afloat


Propeller Shaft Replacement and DNV Approved Rudder Horn Repair while Afloat

Subsea Global Solutions (SGS) recently completed a challenging underwater repair for a commercial ship owner whose vessel had suffered severe grounding damage including a badly damaged propeller, partial loss of the rudder horn, rudder damage, and even a bent main tail shaft. Due to delays in receiving the replacement shaft line and rudder on-site, the emergency drydock slot to complete the repair works ran out and the vessel had to be towed out unfinished to make way for the shipyard's existing priority commitment.  With high costs and insurance implications for towing to a distant drydock, an alternative option was needed. 

Kevin Peters, Director of Technical Sales & Environmental Services explained, “Leveraging our extensive experience, we submitted a comprehensive proposal, embodying our ‘thinking in the water’ philosophy.  Our Technical Services team and in-house project managers crafted a detailed plan which was meticulously reviewed and accepted by all relevant stakeholders, including the vessel owner, classification societies, manufacturers, and hull and machinery insurers where applicable.” 

To enable the in-water repairs, our in-house diver technicians fabricated and installed a customized cofferdam to accommodate the damaged rudder horn at the pier-side lay berth. This cofferdam was carefully planned to allow for the safe and efficient installation of a 10 ton plus main propulsion tail shaft and enable inspections of the shaft line and its bearings to be completed.  New bushes and bearings were fitted and after all laser alignment checks and replacements were completed and signed off, it was time to install the new replacement propeller tail shaft neatly within the stern tube, something rarely if ever done with a ship afloat before.  

Back inside the cofferdam, the damaged rudder horn needed to be permanently repaired by welding on a newly cast steel section to the existing structure. This task required technical design modeling of what part of the rudder horn would be removed and the qualifying a new DNV weld procedure to meet class approval for the permanent repair.  This task also highlights Subsea Global Solutions leading commitment to quality and safety – very few commercial diving companies or underwater service providers possess inhouse technical services expertise that include a dedicated welding engineer and design project team.  

Upon the completion of the rudder horn repair and its detailed Magnetic Particle (MP) inspections and non-destructive testing and evaluation of results (NDE), the final safety and environmental checks and respective approvals were given. This allowed the cofferdam to be removed, enabling SGS to proceed with the manufacturer-approved reinstallation of the new replacement rudder. 

Finally, each of the new variable pitch propeller blades were fitted one-by-one by rotating the new propeller boss above water to restore the vessel's propulsion system to optimal functionality.  Project close out checks of all systems and rigorous testing confirmed the success of the repair work and smooth operation of the systems, ready for the crew to sail again. 

This repair project combined several regular repairs that Subsea Global Solutions undertakes multiple times a year.  By avoiding the need for drydocking, SGS minimized downtime and knock-on costs for the vessel owner, ensuring the vessel could return to service swiftly and safely. The project's success underscores SGS’s expertise, dedication, and capability to deliver high-quality, cost-effective solutions in the marine industry.

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