30m in length. These vessels are often multi-hulled which makes them more stable and moveable especially in rough sea conditions.
245. Service vessels would vary in design and dimensions as they would be required to carry out a variety of different services and operations.
246. Cable laying vessel: There may be up to two separate vessels involved in laying the inter-array and export cables. In one scenario the first vessel would lay the cable on the sea bed and the second would bury the cable. Alternatively one vessel would lay and bury the cable at the same time.
247. Cable laying vessels are typically very large (70m or more) with lots of laydown area to accommodate the hundreds of kilometres of cable needed on an offshore wind farm.
5.4.12 Offshore Maintenance
5.4.12.1 Maintenance activities 248. Once commissioned, the windfarm would operate for up to 25 years. All offshore infrastructure including wind turbines, foundations, cables and offshore substations would be monitored and maintained during this period in order to maximise efficiency.
249. The operation and control of the windfarm would be managed by a Supervisory Control and Data Acquisition (SCADA) system, connecting each turbine to the onshore control room. The SCADA system would enable the remote control of individual turbines, the windfarm in general, as well as remote interrogation, information transfer, storage and the shutdown or restart of any wind turbine if required.
250. There are a number of potential maintenance strategies for the windfarm. The windfarm could be maintained from shore using a number of varying Operation and Maintenance (O&M) vessels (e.g. crew transfer vessels, supply vessels) and/or helicopters – the onshore option. Alternatively the windfarm could be maintained primarily from an offshore base, for example a mother ship (a large offshore service vessel (possibly of the jack up type) or a fixed offshore platform (possibly shared with other infrastructure e.g. a converter station platform or a standalone accommodation and O&M platform within the project boundary) with transfer vessels or helicopters used to transfer personnel to or from turbines and platforms – the offshore option.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 56
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