Vol. 227 No. 12

New rig designs

Walking jackup works nearshore

For conventional jackups, substandard weather can mean costly delays before the platform can function. Fugro Seacore has created the first of a new range of self-contained, walking-jackup platforms. The eight-legged platform, SeaWalker, is capable of walking and safely operating in rough seas, strong currents and on beaches.

The rig, which can function in water depths up to 90 ft, provides access to the transition zone – a difficult area for existing equipment to survey and sample.

The work platform was deployed on a long-term basis offshore Namibia to support the mining of alluvial diamonds in the surf zone. SeaWalker also provides a boost to traditional jackup operations including geotechnical site investigation drilling, trenching, pipeline and cable laying, drilling and blasting.

Each walking jackup can move at about 25 m per hr and has a rapid, deck-elevating system, incorporating eight jackup legs mounted externally to provide maximum stability and unobstructed deck space.

Like traditional jackup platforms, the rig has four jacking legs that can be raised and lowered from fixed jacking points at each end of the platform. In addition, it has another movable pair of jacking legs on each side of the platform. The four auxiliary legs are connected to a sliding frame, which move horizontally along the side of the platform deck.

Once the rig has been towed or moved to its location and is ready to work, the four main fixed position legs are jacked is down to the seabed to lift the platform clear of the water. The two sliding frames, each complete with their legs, are moved forward along the side of the deck as far as possible and the legs jacked down to the seabed to support and take the deck’s weight. The main legs are then retracted off the bottom and the entire platform is moved forward through the two side frames. The main legs are again jacked down to retake the weight for the simple walking cycle to be repeated. The sequence is reversed to walk the platform in the opposite direction.

The walking jackup can function in water depths up to 30 m, providing access to the transition zone.

Fugro Seacore, headquartered in Cornwall, England, has also designed and constructed a larger SeaWalker for a pipeline construction project in Northern Ireland. The design is based on its existing “Skate 4” construction platform. This unit can operate in water depths up to 45 ft.