Project: A2953 Client: East Anglia Offshore Wind Limited Title:


East Anglia THREE– Navigation Risk Assessment 15.5 Impacts of Structures on Wind Masking/Turbulence or Shear


178. The offshore wind turbines have the potential to affect vessels under sail when passing through the proposed project from effects such as wind shear, masking and turbulence.


179. From previous studies of offshore windfarms it was concluded that wind turbines do reduce wind velocity by the order of 10% downwind of a wind turbine. The temporary effect is not considered as being significant and similar to that experienced passing a large vessel or close to other large structures (e.g. bridges) or the coastline. In addition, practical experience to date from RYA members taking vessels into other sites indicates that this is not likely to be an issue.


15.6 Recreational Vessel Blade and Mast Collision


180. The RYA considers the largest risk to recreational craft from offshore wind developments is the risk of rotor blade collision and underwater collision associated with scour protection which reduces the under keel clearance. A collision between a wind turbine blade and the mast of a yacht or damage to the keel could result in structural failure of a yacht.


181. In order to mitigate this risk, the development of the proposed East Anglia THREE


project would adhere to guidance on the construction of windfarms including ensuring that the minimum rotor blade clearance (air draught) for the wind turbines is at least 22m above MHWS. This is the clearance when the blade is in its lowest (six o’clock) position. The actual clearance at a given time would depend upon the prevailing tide and wave conditions, i.e., lower clearance at high water and rough seas, greater clearance at low water and calm seas.


182. To determine the extent to which yacht masts could interact with the rotor blades, details on the air draughts of the IRC fleet are provided in Figure 15.3 based on a fleet size of over 3,000 vessels. IRC is a rating used worldwide which allows boats of different sizes and designs to race on equal terms. The UK IRC fleet, although numerically only a small proportion of the total number of sailing yachts in the UK, is considered representative of the range of modern sailing boats in general use in UK waters.


www.anatec.com


Date: Doc:


07.05.2014 A2539 East Anglia THREE Windfarm Appendix 15.1


Page:


82


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