Six of the buoys are on a two-year contract through Hydrosphere’s increasingly popular hire arm, Hydrosphere Rentals, which provides lights, buoys, chains and sinkers for rental and wind farm operator Statoil has purchased one to remain as a permanent aid to navigation.
“Hydrosphere Rentals was set up a couple of years’ ago and since then has supplied numerous buoys to wind farms and other projects around the UK,” explained Sean Corlett, Hydrosphere’s technical manager, offshore renewable energy. “It’s a very cost-effective solution, saving the need to purchase buoys when they need to be removed at the end of the construction phase.”
Work to develop the wind farm, located around 20 miles off the coast of Cromer in North Norfolk, started in 2015 with the construction of onshore cables.
The Mobilis JET 9000 buoys – two north cardinals, two south cardinals, an east cardinal and two special marks – were deployed by the Trinity House vessel, Galatea over a two-day period to mark the construction area.
The buoys each have a focal plane of 3m with high visibility towers. They are the largest in the JET series and suitable for use in offshore and deepwater locations where a highly visible navigation buoy is required.
For the Dudgeon Wind Farm, the buoys were constructed and prepared in Trinity House’s yard in Harwich prior to being loaded on to Galatea for deployment.
This was overseen by Mr Corlett who explained: “The buoys’ are built as an alternative to GLA Class one or two steel buoys. They are made from medium density polyethylene hull floats with a marine grade aluminium tower and topmark and so are lighter and easier to handle which was a big benefit while they were being deployed.”
He added: “The buoys are perfectly suited to being used in deep water. In this case the water is between 18m to 25m in depth.”
The Dudgeon Offshore Wind Farm is expected to be fully commissioned and providing power to the national grid by the end of 2017. Statoil, Statkraft and Masdar own the wind farm through the joint venture company Dudgeon Offshore Wind Ltd.
The buoys have longer maintenance intervals compared to steel buoys and a modular design allows for commonality of parts, reducing maintenance, inspection, replacement and spares holding costs.
