Boskalis Completes Impressive Aasta Hansteen Float-Over Operation -Photos and Video

Dutch marine company Boskalis has completed an impressive dual vessel float-over operation of the Aasta Hansteen topside in Norway.

Over the last several of years, Boskalis, through its subsidiary Dockwise, has played a critical role in the transportation of the Aasta Hansteen SPAR from South Korea to Norway, along with the topside installation.

With the installation, Boskalis broke a number of engineering records in the process, including the transport of the largest and heaviest SPAR ever, the largest catamaran topside float-over and more than 100,000 worked hours with zero lost time injuries.

The Aasta Hansteen FPSO SPAR is a gas production and storage platform that will be operated by Statoil on the Aasta Hansteen field approximately 300 kilometers off the coast of Norway. The SPAR consists of a lower part, referred to as the hull or substructure, and the topsides on top of the SPAR hull.

Before installation, the SPAR hull was transported horizontally by Boskalis from the shipyard in South Korea to a fjord near Stavanger in Norway. This enormous cylindrical buoy, with a diameter of 50 meters, length of 198 meters and weight of 46,000 tons, was transported by the Dockwise Vanguard earlier this year.

Dockwise vanguard aasta hansteen
Transport of SPAR hull on board of the Dockwise Vanguard. Photo © Flying Focus

Boskalis then transported the 24,300 tons topside which was also built in Korea. This operation was carried out with the White Marlin, the newest and second largest vessel in the Dockwise fleet.

Transport of the topside on board of the White Marlin. Photo © Flying Focus

The third and final phase was the installation of the topside on top of the SPAR hull. Once the White Marlin arrived in Norway, the topside was transferred onto two S-class vessels, the smallest in the Dockwise fleet. The two vessels created a type of improvised catamaran, 

Topside transfer onto the S-class vessels, creating an improvised catamaran structure. Photo © Espen Rønnevik/Boskalis

After accurately positioning these two vessels on either side of the White Marlin, they started un-ballasting whilst the White Marlin ballasted down and maneuvered out from underneath. The result was a sort of catamaran structure with the topside linking the two hulls. Over the weekend, the catamaran structure with the topside was towed out to the vertical SPAR hull.

Topside float over installation with the tip of the SPAR hull above the waterline in between the S-class vessels. Photo © Espen Rønnevik/Boskalis

Once everything was in position above the substructure, the mating operation between the hull and topside was successfully completed.

The topside installed on the SPAR hull. Photo: Espen Rønnevik/Boskalis

A video of the topside float-over is below: