By Steen Drue, Project Manager, A2SEA A/S

Turbine installation work at Gwynt y Môr began on April 30 when SEA JACK started work loading components for the very first of 160 turbine locations. Seven weeks later, SEA WORKER departed from Grenaa, Denmark, headed for the port of Mostyn to join the installation teamwork. In June, the two vessels began working ”side-by-side”, although, in reality, they only occasionally pass each other on the water.

It’s all about timing

SEA JACK is capable of carrying three turbines at a time, loaded on board at the Port of Mostyn in the River Dee. The tidal range and extreme currents in the area are a significant challenge, with port access limited to twice-daily trips at high tide both for SEA JACK and SEA WORKER. This calls for tight coordination between the vessels, particularly in relation to arrivals and departures. For example, it’s important to stick to load-out deadlines or the vessel has to postpone its departure for another 12 hours.

Before starting work, both vessels had to be mobilised to suit the particular conditions of the Gwynt y Môr project. So, even though they had both arrived directly from Anholt after working with the same size and type of turbines, the wind conditions of the Irish Sea required, for example, extra reinforcement of sea fastenings. Modification for the project took around 10 days in a shipyard for each vessel, including preventative maintenance work aimed at making the vessel fit for the entire project period. This latter work primarily involved replacing SEA JACK’s leg wires and overhauling its main crane.

Weather worries

Weather conditions over the summer months for the region are generally very good. So, provided there are no particular challenges with tide or wind conditions (‘unrestricted’ in maritime jargon), the trip from port to wind farm site and back is approximately a five-day cycle. But as winter approaches, the project will most probably run into weather restrictions at some of the planned turbine locations. The chief difficulty lies in the increased wave heights associated with stormier conditions, requiring the vessels to be jacked higher so as to maintain a good distance between waves and the hull.

Preparing for success

To make the most of the difficult weather conditions ahead, careful planning was needed to determine the optimal sequence of turbine installations. Part of this planning process required a detailed study to be performed to find out which of the vessels was best suited to each turbine location.

Working in conjunction with our client, RWE, we jointly defined the optimum installation plan so that each vessel could play to its strengths and any constraints could be fully taken into account. The A2SEA project team closely coordinated activities between the two companies to arrive at the best possible installation sequence. Seabed variations set high demands for the quality of soil data, in particular, in order to overcome the challenges of calculating the most suitable locations for each of the vessels.

Local presence

The 22-man crews on each of SEA JACK and SEA WORKER are accompanied by a wind turbine installation team from Siemens Wind Power with 18 Siemens representatives on board, most of whom are British. In all, approximately 500 people work on the project locally in Mostyn. A2SEA also has its own site office at Mostyn where a minimum of two site managers and one HSEQ officer are present at all times. And the entire operation is supported by a British agency which looks after crew changes, arranging provisions, receiving various goods, and managing an extensive network of local suppliers.

Plain sailing?

Has everything gone according to plan? Not quite. Bad weather saw SEA JACK unable to pass Lands End for almost three weeks, turning a seven-day journey into almost thirty. A situation like that calls for flexibility, so we used the waiting time to our advantage, transporting technical staff out to the vessel to perform final preparation at sea instead of in port as originally planned. As a result, SEA JACK was ready to work almost from the moment it was finally able to dock. The project had its share of good luck, too – an unexpectedly mild, low-wind summer in the Irish Sea compensated nicely for the three weeks lost.

As unavoidable as it may be, a situation like that calls for flexibility. The company used the forced waiting time to its advantage, transporting technical staff out to the vessel to perform the final preparation work at sea instead of in port as originally planned. As a result, SEA JACK was ready to go to work almost from the moment it was finally able to dock.

Spanning 79 square kilometres, RWE Innogy’s flagship Gwynt y Môr offshore wind farm is currently the largest site under construction anywhere in Europe. A €2 billion project, Gwynt y Môr comprises 160 Siemens 3.6 MW turbines, offering a total of 576 MW of energy – enough to power around 400,000 homes. The farm is being built by RWE npower renewables in Liverpool Bay, off the North Wales coast, and is funded by RWE Innogy, Stadtwerke München GmbH, and Siemens AG. The wind farm is due to be fully operational by the end of 2014.

 

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