Download - BMT Nigel Gee Ltd
BMT Nigel Gee Ltd
The Transport and Installation of Concrete Wind Foundations
European Offshore Wind 2009, Stockholm
Mark WillbournMarketing Director
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
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
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
Concrete Foundation Design
• Pre-stressed concrete
• Slipformed stem
• Reduced stem diameter at sea bed level
Onshore Construction Site
Offices / Workshops
Building Pads
Load Out Quay
TIB
Launch of Foundation
Vertical Launch Platform
TIB Connected Over Foundation
Base UnitTIBVertical Launch Platform
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
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
TIB Under Tow
Maximum Hs = 3.0m
Operating Context
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
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
TIB Disconnected
• TIB disconnects from Base Unit
• TIB deballasted with compressed air and towed off
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
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
Thank You