DOT 2010: Closed Centerwell truss spar explained

Technip’s Anil Sablok and Wade Mallard gave the attendees of the Deep Offshore Technology (DOT) conference a presentation on a new truss spar configuration called the “closed centerwell (CCW) spar."

Offshore staff

HOUSTON – Technip’s Anil Sablok and Wade Mallard gave the attendees of the Deep Offshore Technology (DOT) conference a presentation on a new truss spar configuration called the “closed centerwell (CCW) spar."

The truss spar has been developed to reduce hull diameter and weight over the conventional open centerwell (OCW) truss spar for the same payload, without sacrificing the exceptional motion characteristics of the spar, say the authors.
The key to these enhancements, they say, is that, by closing in the hard tank section of the centerwell, the CCW spar generates additional buoyancy while retaining the functionaly of the centerwell. This increased buoyancy supports greater topside, riser, and mooring payloads for a given hull diameter and length. Significant hull weight savings can be achieved relative to a conventional truss spar.

The smaller CCW spar hull is more flexibile in terms of fabricating and transporting the hull in one piece using existing fabrication facilities and transport vessels. Similarly, the reduction in CCW spar hull diameter facilitates lifting heavier topsides in one piece or larger modules, by allowing the heavy-lift vessel to be positioned closer to the centerline of the hull. The reduction in the size also reduces environmental loads on the hull permitting smaller mooring considerations. The CCW spar benefits further from incorporation of an improved compressed air ballasting system with higher variable ballast capacity from additional ballast tanks that can better accommodate the platform variable payloads that accompany retrofitting of risers and production equipment upgrades.

The presentation included a description of the truss spar closed centerwell concept and compared it to the existing open centerwell designs. Model test results were compared to those from an existing, equivalent open centerwell design. The comparisons showed that the CCW truss spar design retains the desired low motion characteristics of the existing truss spars, while presenting competitive advantages associated with its reduced hull diameter, weight and cost.

2/2/2010

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