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BMT Nigel Gee Ltd

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  1. BMT Nigel Gee Ltd The Transport and Installation of Concrete Wind Foundations European Offshore Wind 2009, Stockholm Mark Willbourn Marketing Director

  2. BMT Nigel Gee • Specialised in Naval Architecture and Marine Engineering Design Consultancy – part of BMT Group • Particular expertise in “specialised vessels” – high speed, low wash and vessels with excellent seakeeping characteristics • Experience in innovative new designs – 80m high speed catamaran for US Navy and patented 220m Pentamaran hull form • >150 vessels built to BMT NG designs – up to 220 LOA • BMT can provide not only design consultancy, structural and seakeeping analysis, etc. but also full construction detailed design packages for operators and shipbuilders and ship repair yards worldwide

  3. Study Background • Gifford approached BMT NG to assist in Concrete Foundations study following earlier feasibility study on suitability for wind farm foundations. • BMT NG’s specific task was to provide innovative but workable solutions to task of moving large foundations to wind farm sites. • Study work included review of: • Structural requirements for “vessel” • Stability assessments • Latching mechanism • Towing requirements • Seakeeping assessments • Logistics analysis

  4. Study Objectives • To provide an integrated systems approach to the tasks: • Coordinate design and construction of foundation and installation methodology for efficient production • Use conventional concrete construction technology onshore • Maximise operational weather window for offshore transit and installation • Minimise reliance on expensive offshore heavy lift equipment • Use relatively simple barge concept for transport and installation

  5. Concrete Foundation Design • Pre-stressed concrete • Slipformed stem • Reduced stem diameter at sea bed level

  6. Onshore Construction Site Offices / Workshops Building Pads Load Out Quay TIB

  7. Launch of Foundation Vertical Launch Platform

  8. TIB Connected Over Foundation TIB Vertical Launch Platform Base Unit

  9. TIB Features, for 3600 Te Foundation LOA : 34 m Beam : 32 m Minimum Draft : 6.2 m Operating Draft : 9.0 m Required Water Depth with Foundation Unit : 11.3 m

  10. TIB Features • Dumb barge, power only for ballast and latching systems • Unmanned barge for normal operations • Simple for remote operation • High lift and transport capacity • Relatively fast system

  11. TIB Under Tow Maximum Hs = 3.0m

  12. Operating Context

  13. Seakeeping Analysis • Undertaken using VERES programme in-house by BMT • Operating criteria based on forces and motion limits that foundation could reasonably expect to withstand and safety margins • Motion criteria for placement of foundation on sea bed are significantly more restrictive then for transit : • Impact force on sea bed • Risk of foundation bouncing on sea bed • Risk of distortion of prepare bed • Transit criteria – no significant restrictions up to 3m significant wave height • Placement criteria – limited to 1.25m significant wave height, depending on water depth

  14. TIB and Foundation Placed on Sea Bed • TIB ballast tanks flooded under control to place Base Unit onto sea bed • Maximum significant wave height Hs = 1.2m

  15. TIB Disconnected • TIB disconnects from Base Unit • TIB deballasted with compressed air and towed off

  16. Manoeuvring Simulations • Not yet completed but BMT has PC Rembrandt to undertake bespoke simulations to enable operations and tow masters to: • Establish safe operating limits • Investigate tow and handling strategies • Assess risks for tows • Assess marine issues for installation and de-comissioning • Assess mooring arrangements

  17. Conclusion • Adaptation of existing technologies can provide low cost solution to transport and installation of concrete foundations • Seakeeping analysis has determined that transport is feasible in up to 3m significant wave height • Installation is possible in up to 1.25m significant wave height, depending on water depth • Use of TIB concept could enable installation operations in wider weather windows • As foundations get larger, operating window extends

  18. Thank You

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