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Greater Gabbard

Greater Gabbard

This £0.45 million contract involved the installation and commissioning of a meteorological mast for wind measurement in 6-8m water depth, with a 2 kn current on the Inner Gabbard Bank for Greater Gabbard Offshore Wind Limited (GGOWL) owned by Airtricity and Fluor.

The installation of the mast is part of the ongoing development by GGOWL to produce the Greater Gabbard Project, one of four Round 2 sites in the Thames Estuary anticipated to have a total capacity of 500 MW. Greater Gabbard is one of the furthest sites from land and offshore methods were adopted both for preparation works and during the construction phase.

Installation works were executed from Seacore's 8 leg jack-up Excalibur which is capable of storm survival at such locations and can support all of the required installation and commissioning plant, equipment and personnel with little or no shore support. Excalibur was mobilised to Great Yarmouth and with the assistance of Seaforth-Maritime Ltd, carried out all logistics necessary to bring the various components to the vessel for loading. Excalibur's width caused restrictions on vessel movement within the river Yare and the port authority requested her time alongside to be minimal, so significant planning went into site logistics during the mobilisation phase. Mast sections, platform assembly and monopile were loaded onto Excalibur and sea-fastened ready to sail to site within the programmed 7 day period alongside.

The metmast site was 40 nautical miles due south of great Yarmouth and seagoing tug Eurosund was mobilised from Denmark to tow the jack-up from Great Yarmouth. Eurosund was also contracted to act as guard vessel during site works because of the distance from shore.

For vessel positioning and further survey for monopile plan position, orientation and elevation a Fugro Starfix HP system was installed which incorporated dual DGPS receivers on board linked to a calibrated gyro-compass. Once on location and jacked to the required elevation, operations commenced with positioning of the pile handling system.

The monopile was lifted from its sea fastenings and "topped to tailed" using Excalibur’s Demag PC1200 ring lift crane. The 59m long x 1.8m dia. x 136t pile could be lifted safely and easily because of the twin hook "chandelier" arrangement on the crane.

Once oriented and held vertical in the pile gates the monopile was hammered to final elevation using a Menck MHU 500T hydraulic hammer. The metmast’s platform was lifted onto the pile top and welded in place, before 3rd party team Comsec commenced metmast erection. Excalibur remained on location enabling Powerpoint Ltd to commission the measuring equipment.

Following a delayed commencement date the Greater Gabbard Met Mast installation was finished on time, to programme and was entirely incident free.