Thanet Offshore Windfarm construction forges ahead
A milestone has been reached with the installation of the offshore substation at Vattenfall’s Thanet Offshore Windfarm off the UK’s Kent coast.
Around 35 vessels ranging from support craft to installation vessels are involved in the three main elements of the project; turbine installation, the offshore substation and the associated cabling works. At the time of writing all 100 foundations, 89 transition pieces and 31 turbines have been installed.
Since March 2009, A2SEA’s jack-up platform Sea Jack has installed the monopile foundations and navigation markers transferred from Vlissingen to Ramsgate by Osprey Shipping’s tug Osprey Fighter and the barges Osprey Carrier and E3501. Danish owned tug Stevns Arctic has supported the Sea Jack together with among others Viegers’ Shoalbuster Bever and Driemast BV’s tug Meander providing assistance at Ramsgate.
By May 2009, with around 20 monopiles installed, MPI Offshore’s installation vessel MPI Resolution commenced installing the transition pieces, loading out of Vlissingen. By November, with 84 transition pieces in place, the MPI Resolution switched roles to installing the actual turbines, which were by then loading out of Dunkirk. In January of this year the installation of the 100th monopile by the Sea Jack was celebrated. That vessel then took over installing the remaining 14 transition pieces, which were transferred to Ramsgate six at a time from Vlissingen.
A variety of craft including the cable lay barge UR101, chartered by main cable contractor, Aberdeen based Subocean Group, have been busy laying the inter-array and export cables, supported by a variety of craft including JP Knight’s ASD tug Keverne and Multraship’s ASD tug Multratug 18. Initially the UR101 was employed on the inter-array element but was later switched to the task of installing the export cable.
Two sophisticated offshore support vessels have been mobilised by Subocean to install the inter-array cables and in October 2009 a renewable industry milestone was passed when the Norwegian owned cable layer Polar Prince became the first vessel to install inter-array cables utilising DP. Four cables were buried 1m below the seabed in 30m of water in just 24 hours, a method claimed to cut installation time by 50%. In December 2009, just days after the first turbine was installed, the Norwegian owned, Isle of Man registered DP2 class support vessel Normand Mermaid joined the Polar Prince laying the inter-array cables. The UR101 meanwhile was busy establishing the shore end of the export cable to the onshore substation at Pegwell Bay south of Ramsgate.
The offshore substation was installed in January 2010. Claimed to be the largest in the world, a jacket style foundation was adopted to support the three level topside structure. The Russian owned crane ship Stanislav Yudin, operated by Dutch company Seaway Heavy Lifting, was mobilised for this operation, supported by the anchor handling tugs Blizzard and Typhoon from ITC Holland BV, Harms Bergung Transport’s tug Centaurus, and the Spanish ASD tug Red Wolf. Upon completion the Stanislav Yudin returned to Rotterdam, with Fugro-Seacore’s jack-up Excalibur continuing the substation installation work.
Space precludes a mention of all the craft involved but cable mattress installation work is finally underway by Vroon Offshore’s Oil Express, supported by various craft including the tugs DMS Globe, Voe Jarl and Red Dolphin. By Peter Barker
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