Wind farm project is workboat magnet
The construction of the Gunfleet Sands wind farm off the Essex UK coast got underway at the end of August, since when a fleet of specialist vessels has arrived in the area.
The Gunfleet Sands site is approximately 7km south east of Clacton-on-Sea, occupying an area of 17.5k m². There are 48 turbines to be installed, each with a capacity of 3.6MW, giving a total output of 172MW. The turbines will have a maximum height of 129m from blade tip to sea level with a rotor diameter of 107m.
Each monopile is 5m diameter, 50m tall and weighs 400 tons. They will be driven up to 40m into the seabed by hydraulic hammer. The transition pieces, which are painted yellow for visibility, are then mounted on top of the monopile by the Svanen. Each transition piece weighs 230 tons and is 23m tall. The total time to install a monopile and transition piece is under two days.
The turbines will be positioned with a spacing of 435m x 890m. A temporary 500m safety zone has been established around the site during construction but once the construction phase is over fishing and leisure craft will be permitted to pass through the wind farm site.
The heavy lift vessel Svanen is a self propelled catamaran with a lifting capacity of 8,700 tons. On November 11 the vessel came into Harwich International Port (Parkeston Quay) for routine maintenance, assisted by its support vessels, the newly built tug Sea Alfa (2008, 309gt), managed by Seacontractors BV, and Marineco UK’s multicat Marineco Hathi (2008, 154 gt), along with Briggs Marine’s multicat Forth Constructor (1967, 265gt) and one of Svitzer’s Felixstowe harbour tugs escorting. The vessel departed Harwich three days later with one tug and one multicat.
The Svanen is operated by Ballast Nedam Offshore Energy of the Netherlands. It is able to manoeuvre with maximum crane load without the help of tugs, although Sea Alfa and Marineco Hathi are usually in attendance on this project for anchor handling and other support duties. The vessel is 102.75 m long with a 71.80 m moulded breadth and a draught of 6.0m. It has a hoisting height of 76m and its unique design enables it to collect, transport and place elements with an accuracy of a few centimetres. Its sailing speed is 7 knots. While Svanen works in deep water, the jack-up barge Excalibur will be installing monopiles in shallower water.
The Smit Barracuda (2006, 230gt) and barge Molus were waiting at Parkeston Quay for some weeks to supply Svanen with piles and transition pieces, along with another Smit tug, Eerland 26 (1967, 127gt) and barge E 3801. The Herman SR tug Baloe (2006, 126gt), with the 1,482 gt spud barge Oceanteam Installer, operated by Norway’s Oceanteam P&U, had been alongside at Harwich for longer.
The latter is a flat bottom barge, 65m long by 22m wide, suitable for shallow water operations and for grounding. It is built for installing underwater cables and is equipped with a crane, two spud poles, two thrusters, four point mooring system and pull winch. This will be used to run cabling from the offshore transformer sub station to the shore at Holland Haven in a 2m deep trench.
The cable installation barge, Eide-28 was also due to begin installation work and the crane barge Anna 4 was due on site in November to place a pedestal for the substation. Anna 4 was to be towed by the tug Stadt Master and supported by the Pushycat Smit Bison.
The Haven Seaforth spud leg barge, operated by the newly re-named company Red 7 Marine (ex Haven Ports) is also on site as a diving support platform for installing J-tubes for the cables over low water, with associated workboats and the Shoalbuster tug MTS Valour assisting.
Other vessels working on the Gunfleet project include the small survey vessels Arie Dirk, Cacheflow and Sophie Lea, involved in noise monitoring, marine mammal and bird observations. There are also many crew boat movements between the wind farm site and the local port of Brightlingsea.
By Graeme Ewens
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