Access stairs: jack-up to WNA & WNB

The Scope

A light, modular stairway was required to quickly and safely access the Vermilion Oil and Gas (VOGA) Wandoo A platform helideck from the Noble Tom Prosser (MODU) cantilever deck 7.5 metres above.

Cube Offshore were contracted to design, manufacture and test a fully functional solution.

Several months later, a similar requirement arose to safely access the Wandoo B platform main deck from the Tom Prosser cantilever deck. This configuration resulted in a 9.5m vertical separation between decks, the landing area was more remote and the stair was to remain attached to the cantilever during skidding activities.

The Outcome

Cube’s design solutions for Wandoo A included the following:

  • Weight – aluminium design used for significant weight reduction
  • Transport  – split into two modular parts for road transport & manual handling into position.  Each part certified for offshore lift so no baskets required.
  • Installation – simple bolt connection in middle for assembly.  Upper end stabbed into guide / Lower end on heavy duty castors
  • Significant relative motions between Wandoo A and Noble Tom Prosser cantilever accommodated by incorporating a swivel hinge at the top and rollers at the base

The Wandoo A stairway was to delivered on schedule and to budget. The stairway was transported, assembled and deployed safely and quickly.

The requirement at Wandoo B was not forseen by VOGA. However, Cube was able to reuse the two existing halves by adding a middle section (see photos below). This creative design for a new application saved VOGA significant time and cost.  All pre-existing design requirements were met.

Elevation of WNA aluminium access stair

Stair pre-assembled inside the Tom Prosser cantilever module

Stair lifted and stabbed into pre-installed sockets in the mousehole gutter opening

Access stairs landing on the WNA helideck

Hatched area on WNB main deck shows stair landing area subject to cantilever skidding requirements

Re-use of WNA stair sections for WNB application with the addition of a central tower section

3D isometric of WNB aluminium access stair

View looking down WNB access stair tower, onto the WNB main deck from the Tom Prosser cantilever