NG-9000C raises the bar in the wind turbine market

GustoMSC’s NG-9000C installation units include a host of innovations such as the company’s ‘wrap around the leg’ crane. Two yards are building three units

Development of offshore windfarms is proceeding apace in many countries, particularly in Europe, and China and the US are not far behind.

The UK has set a major challenge with its Round 3 programme to install a massive 32GW-plus of capacity. Translated into numbers this will create a need for more than 6,000 turbines and around 100 transformer platforms and transmission cables to shore. All this needs to be done ‘faster, cheaper and safer’ in water depths of up to 70m.

However, as OSJ has highlighted before many times, new units have been ordered but the number of installation vessels that will be needed to install all of these turbines is large. As yet few have entered service.

The units must be able to install foundations, transition pieces, towers, nacelles and hubs plus rotors. Ideally they should be able to install a foundation or tower plus nacelle in 1-2 days and have a dynamic positioning system, which would allow them to operate without mooring lines.

GustoMSC in The Netherlands is long-established as a designer of offshore units such as jack ups and has also made a name for itself as a designer of wind turbine installation units. Its business development manager Gerrit Jan Schepman explained that some of the units now at work in the market have their roots in GustoMSC designs. Examples include Sea Worker, JB-115, JB-114, Seajacks Kraken and Seajacks Leviathan, MPI Resolution, Vagant, Buzzard, Wind Lift I, Stanislav Yudin and Svanen.

The latest additions to the fleet are the first of the ongoing NG series. These proprietary GustoMSC designs are four-legged units with DP2 positioning, a high jacking speed, efficient cranes and large, variable load and deck space.

Seajacks Kraken and Seajacks Leviathan, of NG-2500X class, are now active in the Greater Gabbard field. Wind Lift I, of NG-5300 class, is working on the BARD Offshore 1 project. MPI Adventure and MPI Discovery, of NG-7500/6 class, are under construction at Cosco Nantong Shipyards in China for delivery in 2011.

The latest addition to this evolving family of wind turbine installation units is the NG-9000C class, two examples of which are being built for Fred Olsen Windcarrier by Lamprell Shipyard Ltd in Dubai following their order in February 2010. Delivery will be in mid-2012. Drydrocks World SEA also began construction of the first NG-9000C in December 2009 for delivery in early 2012. This yard also recently built four SEA2000 units of which three are active in wind turbine installation projects.

Interesting and innovative features of the NG-9000C include:

. a large, variable load of up to 6,500 tonnes;
. a high transit speed of about 12 knots;
. a full DP2 positioning system;
. a ‘continuous cylinder’ jacking system; and
. a ‘wrap around the leg’ 800 tonne crane.

Each unit’s variable load and large net deck space enables it to transport 10 sets of 3.6MW wind turbines in one haul. “For different projects one can see that the selection of the hub and, more specifically, the hub port largely determines the sailing time of the vessel,” Mr Schepman explained. “With all new field developments, these hub ports are also under development. In general, sailing distances of 300 miles [480km] should be considered. Consequently the transit speed of the vessels needs to be optimised to reflect this.”

This being the case, the NG-9000C has a proven hull shape and three 3,500kW azimuthing thrusters that allow a transit speed of 12 knots. So a 480km haul would take about 30 hours.

The vessel’s DP2 system allows quick and efficient positioning at the desired location and its capability is tuned towards the maximum jacking condition. In 1.8m significant waves, wind of 14m/sec and current of 1m/second the vessel can remain on location with the legs lowered close to the seabed. “DP is a must for fast and efficient operations as no tug boats or mooring system need to be deployed,” said Mr Schepman.

The NG-9000C is the latest development of the GustoMSC continuous cylinder jacking system. This ‘pin-in-hole’ system operates with four jacks per leg, of which three systems are engaged, elevating or lowering, while one is in the recycle mode. The system enables a lifting speed of 29m/hour at maximum elevated weight. The leg handling speed is up to 40m/hour.

The pre-loading operation to secure the vessel takes place after touchdown of the legs. Mr Schepman says one of the advantages of the four-legged unit is its fast diagonal pre-loading. In elevated condition, the vessel can withstand – with full variable load – the year-round survival condition of 10.8m significant waves, 41m/second wind and 1.25m/second current in a maximum water depth of 45m.

The accommodation deckhouse is at the forward end of the vessel, while the engine rooms are in the ship’s centre – away from the accommodation spaces. Four diesel generator sets of 4,300kW each power the vessel. The diesel-electric machinery provides power to 6.6kV main bus bars. The thrusters, HPUs and main crane receive powered through the 690V switchboards and the 440V and 220V switchboards complete the electrical system on board.

The innovative ‘wrap around the leg’ column crane is GustoMSC’s way of providing efficient installation lifts and of freeing up the deck for the storage of wind turbine modules. “Locating the crane at the edge of the free deck area means that the deck area served by the crane hook is maximised,” Mr Schepman told OSJ, “and by positioning the crane close to the side of the jack up the most effective use of the crane’s outreach is obtained, but the work space is still obstructed by the legs. Observing this, it is an obvious solution to arrange the crane around one of the jack-up legs.”

The principle of this arrangement is not totally new. In 1968 the jack up Cowrie One, which Gusto Shipyard in The Netherlands built, had a small crane around the leg. However, the NG-9000C’s specification of the crane around the jack-up leg – 800 tonnes at 24m outreach – is much more ambitious than this example from the past.

“GustoMSC currently has a portfolio of cranes ranging from 500 to 5,000 tonnes lifting capacity, and development work at the company is currently oriented towards the combination of proven components into a new crane concept rather than using novel technology to meet the design criteria,” Mr Schepman told OSJ. “Our column cranes, which have a lifting capacity in the range of 500 tonnes to 1,000 tonnes, are located on an individual pedestal and supported by an integrated three-race roller bearing or a king-post bearing combined with horizontal bearings at two elevations. Large offshore cranes with a lifting capacity of 4,000 to 5,000 tonnes of the type that are being built for large offshore construction vessels are located on a large diameter tub and supported by a bearing system composed of bogie wheels. The ‘wrap around the leg’ crane uses components from both of these concepts.

“Since the jack-up leg penetrates through the centre of the crane, the bogie-wheel bearing system was adopted. A relatively large diameter circular bulkhead supporting the bogie wheels is designed on top of the jack house, thus providing sufficient internal free opening for the leg to penetrate. The fitting of individual sets of bogies to compose the bearing system also serves to decouple the construction of crane and jack-up leg.” OSJ