When an LNG carrier experienced steering-gear issues, the initial suspicion was damage to the rudder equipment. A shipyard inspection in Portugal confirmed the problem: the rudder stock had suffered torsional deformation in the upper keyway area.

MarineShaft specializes in class-approved repairs of complex and critical damage to rudder and propulsion equipment. With workshop facilities in Denmark and on-site repair capabilities, the company assists shipowners, ship management companies, and shipyards with emergency repair solutions.

The twisted rudder stock required multiple repair techniques. The challenge was not simply to straighten the rudder stock. Although class-approved cold straightening could restore the required straightness and run-out, straightening alone could not remove the torsional twist in the keyway area.

Rebuilding the geometry

MarineShaft provided a repair solution that addressed the complete rudder arrangement.

The solution was to rebuild the damaged upper keyway area by welding up the existing keyway and machining a new keyway in the corrected position. The associated rudder components had to be adapted to match the repaired rudder stock.

The owner sent the rudder stock and steering equipment to MarineShaft’s workshop in Denmark, where the repair started with a run-out measurement and an NDT inspection.

Workshop repair scope

After cold straightening, the rudder stock underwent another NDT inspection. The rudder stock sleeve was removed, and the damaged areas on the rudder stock were machined in preparation for welding.

MarineShaft welded up the existing keyway to compensate for torsional deformation, including welding surface damage on the rudder stock.

Before and after welding, a third party carried out magnetic particle inspections to check for cracks.

After welding, post-weld heat treatment (PWHT) was carried out to relieve residual stresses in the welded areas of the rudder stock. The new keyway was then machined in the corrected position. Using stock material, MarineShaft manufactured a new rudder stock sleeve and shrink-fitted it onto the rudder stock.

Modifications to the mating rudder components

Correcting the keyway position on the rudder stock also required modifications to the components mating with the repaired rudder stock.

The tiller was reconditioned by machining the fork surfaces in preparation for welding. Following welding and PWHT, it was machined back to its original dimensions. Magnetic particle inspection was performed by a third party.

Ovality in the tiller cone was removed by machining to restore the correct geometry, while the tiller keyway was machined to match the new keyway position on the rudder stock. The carrier flange was also machined as part of the complete reconditioning scope.

Finally, the rudder stock cone was blue-fitted to the tiller under the supervision of a DNV surveyor, who approved the fit.

Completing the repair on-site in Portugal

MarineShaft service engineers travelled to the shipyard in Portugal with portable machining equipment. Their job was to machine the upper rudder blade cone and cone keyway to ensure that the repaired rudder stock could be fitted correctly into the existing arrangement.

MarineShaft also supervised the final blue fitting.

By combining workshop repair, component modification, and on-site machining, MarineShaft delivered one coordinated repair solution from inspection to final fitting.