Rotterdam, The Netherlands The pioneering use of a free floating vessel for both transportation and installation enabled the TPs to be placed at the 500 MW Greater Gabbard Offshore Wind Farm (GGOWF) at an unprecedented rate, according to the Netherlands-based contractor.
With Jumbo’s heavy-lift vessel Jumbo Javelin holding its place using dynamic positioning (DP) – a computer-controlled system that locks ships in precise locations – 131 of the farm’s 140 transition pieces were installed a month ahead of schedule.
The transition pieces, which link piles in the seabed with the steel turbine towers, were put in at a pace of more than one per day, which Jumbo Offshore claims as a record. The job involved leveling and grouting and was completed without serious accidents, according to the company.
Jumbo was working for Fluor, which has a contract with Scottish and Southern Energy plc (SSE) for design, supply, installation and commissioning at the Greater Gabbard wind farm, whose 140 3.6 MW Siemens turbines are in depths of between 24 and 34 metres.
The entire construction, which covers two areas 25 km off England’s Suffolk coast by the Thames estuary, should become the world’s largest offshore wind farm on its scheduled completion in 2012.
In March 2010 the Jumbo Javelin was outfitted with temporary living quarters, a grout plant and an Ampelmann access system – a ship-based, self-stabilizing access system that actively compensates all vessel motions, giving the crew safe access to the installed TP and helping guide the grout hoses.
Jumbo also developed and built its own passive lifting compensators (with a 2.5 m stroke and a safe working load of 300 tonnes) and two job-specific, remote-release operated, spreader bars to lift the TPs.
The ship sailed from the port of Flushing to the offshore location with nine 280 tonne TPs. Each TP was placed in the specified orientation and levelled to its final position. The annulus (the space between TP and monopile) was then filled with grout to fix it permanently.