Suction bucket is ready to sail

Load-out of a pioneering three-legged foundation design that could slash the cost of offshore wind  power is imminent at Bladt Industries' Aalborg yard, with developer Dong Energy now expecting to lift the structure onto a waiting installation vessel tonight for transport to the Borkum Riffgrund 1 development off Germany.

The so-called suction-bucket jacket, fitted with cylindrical-shaped feet that are pulled down into the seabed by a system of high-pressure pumps, was to have sailed out yesterday to the 312MW wind farm now under construction off the island of Borkum, but poor weather delayed the launch.

The 850-tonne steel structure, which stands 57-metres tall, will be installed in 24-metres of water by Swire Blue Ocean's Pacific Orca jack-up unit and topped with an upscaled SWT-4.0-130 Siemens turbine as part of a technology demonstration project.

Suction bucket foundations are an import from the offshore oil industry, where the technology has seen widespread use for many years.

Unlike conventional jackets, which are anchored to the seafloor with hammered-in piles, the suction bucket design is lowed from the installation vessel to seabed, where pumps create a vacuum under each caisson that secures them, and a thin layer of grouting is injected to cement the seal.

Suction bucket foundation designs, which are targeting the coming 6MW-plus wind turbines on projects in water depths of 30-60 metres, are under development at a number of companies, including Fred Olsen-backed Universal Foundation, which has its flask-shaped concept piloted topped by met masts at Forewind's Dogger Bank mega-development.

Dong aims to have its design proven in time for the UK's Round 3 projects.

The suction bucket jacket-based turbine will stand at the heart of Borkum Riffgrund, which is built around 77 traditional monopile-based machines.

First power from the wind farm is slated to begin flowing later this year with the development reaching full production in the first half of 2015.