Vessel Repairs

OPC designed replacement steering cylinder foundations for Aurora G, an aluminium standby safety vessel classed with RINA. The work was undertaken for Marine Repair B.V. following cracking of the existing starboard foundation.
The scope covered replacement foundations on both sides of the vessel, together with structural calculations and drawings for class approval.

Developing the Repair

The design needed to transfer the steering cylinder forces into the vessel’s existing aluminium structure. An initial arrangement supported by the longitudinal stiffeners was investigated, but their size and the applied loading prevented a satisfactory solution within the RINA rule requirements.
The replacement foundations were therefore designed to span between transverse web frames. This provided a stronger supporting arrangement and distributed the steering loads into the surrounding hull structure.
Grade 5083 aluminium was specified for the new foundations, with the material condition and design properties selected to suit welded construction and the applicable class requirements.

Structural Verification

OPC developed a finite element model incorporating the new foundations and the supporting vessel structure. Including the surrounding structure allowed the assessment to examine how the steering loads were transferred beyond the cylinder mounting points.
Two steering positions were assessed, covering both in-plane loading and the additional out-of-plane force at an angled rudder position. The analysis checked stresses and deflections, with an eigenvalue buckling assessment used to evaluate structural stability.
The calculated stresses were within the adopted RINA allowable limits, and the analysis demonstrated sufficient structural capacity for the assessed loading conditions.

Drawings and Class Approval

The engineering package included a structural design report and detailed arrangement drawings defining the replacement foundations, plate thicknesses and connections to the existing structure.
RINA approved the structural arrangement in January 2023, with requirements for welding details and verification by the attending surveyor. The approved package provided the technical basis for the foundation renewal.