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