Making light work in heavy lifting

The Rambiz 3000 carrying Wintershall’s L6-B mono-tower platform. Image from Scaldis.

Belgian and Dutch contractors have taken minimal facilities to the next level by installing a mono-tower platform and its foundations together, and in record time using a unique “single lift” operation.

By transporting the entire 1360-tonne structure—a mono-tower, topsides, and suction can foundations—on the lifting hooks of heavy lift vessel Rambiz 3000, Wintershall Nordzee and Scaldis Marine Contractors were able to perform the installation in four days, including sailing and demobilization time, to complete the project on 7 June.

The project involved Wintershall’s L6-B field development, which comprises an unmanned, remote controlled, minimal facilities platform on a tripod structure, with suction can foundations in Block L6, in 38m water depth, in the Dutch sector of the North Sea.

Belgium-based Scaldis Salvage & Marine Contractors’ heavy lift vessel Rambiz 3000 lifted from the quayside and then transported the tripod and minimal facilities topsides as one piece on its hooks. It was then installed on location in four days including sailing to the field, installation, and demobilization to port.

SPT Offshore was subcontracted by Scaldis and was responsible for the tripod concept design, as well as the three suction piles’ design and installation. This happened simultaneously, in just three hours, by reducing pressure in the voids inside the suction cans so that they penetrated to 10m below the seabed, with the monopile just 0.011° out of vertical. The rigging was then disconnected, the hydraulic spreader bar door opened and released from the structure.

For the project, Dutch firm Innovation Input designed a new, 4000-tonne capacity spreader beam, following a previous order for a 3300-tonne sub-spreader beam, at 11m-25m long. The new beam is intended for it to be used on Scaldis’ new vessel Rambiz 4000, as well as as a “tri-pod handling beam” on the existing 3300-tonne capacity vessel Rambiz 3000.

To handle a “tri-pod type wind turbine foundation,” a hydraulically-driven and demountable clamping device was added to one side of the beam to hold the main monopile tower section in place. The other side of the beam has counterweights to maintain balance. Lifting forces via steel wire lifting rope connected using hydraulic shackles to the structure’s base (the suction cans), are re-routed through self-adjusting spreader heads, at each end of the beam. The beam is also buoyancy-compensated for underwater use. The beam was delivered in May 2014 and offshore mobilization started early June.

The topsides, monopile and foundation structure were fabricated by NAMI constructions on the Franklin Offshore yard in Rotterdam.