AKOFS Offshore has with the vessel Aker Wayfarer installed 9 manifolds on the seabed on ultra deep water for Petrobras. The heaviest weigthed 230 tonnes and was installed at approximately 2200 m.
Aker Wayfarer has a unique fibre rope deployment system with capacity of up to 300 tonnes down to 3000m in “two falls”, alternatively 150 tonnes to 6000m if necessary. The unique feature with the fibre rope is that it is neutrally buoyant in water. Contrary to the normal steel winches, the lifting capacity is not reduced with the water depth as the weight of “paid out” rope weigh nothing in water. The weight of a steel wire at deep water will take a significant part of the payload, requiring a capacity of the crane far in excess of just the weight of the item to be installed.
The manifolds have been over-boarded by use of Aker Wayfarer’s conventional 400t active heave compensating crane and submerged to approximately 200m below the sea surface. At this point, the Aker Wayfarer’s fibre rope deployment system, acting through the moonpool, takes over the load and the 400t AHC crane is detached. The descent to the sea bottom is continued from this point, maintaining the fire rope deployment systems full load capacity.
Typical turn around time for such an operation, from the manifold is picked up at shore, installed, and vessel back to shore for other tasks, is in the order of one week
The typical alternative to using the features of Aker Wayfarer, is to have specialized heavy lift vessels mobilized to Brazil, as no such vessel is presently receding in Brazil. This has high cost with mobilization and demobilizations, and high rates for specialized vessels, as well as additional GHG emission from long transits of large vessels.
