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Feature 5 | JACK-UP RIGS

• Large variable load of up to 6500tonnes;

Some of the benefits of the NG-9000C wind turbine installation unit are:

• High transit speed of approximately 12kts;

• Full DP2 positioning system;

• Continuous cylinder jacking system; and

• Wrap around the leg 800tonnes crane. Te large variable load and the large net

deck space of the unit enables five complete wind turbine sets to be transported to one haul. For the 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. With all new field developments, these hub ports are also under development. In general, sailing distances of 300miles should be considered. Consequently the transit speed of the vessels is to be optimised. Te NG-9000C has a proven hull shape

and with the three 3500kW azimuthing thrusters, a transit speed of 12kts can be achieved. Tus for a 300miles haul, transit time is approximately 30hrs. Arriving on location, the vessel is equipped with a DP2 dynamic positioning system, enabling the vessel to position at the desired location. Te DP system capability is then tuned towards the maximum jacking condition. In 1.8m significant wave heights, 14m/s wind and 1m/s current, the vessel can remain on location with the legs lowered near to the seabed. DP is a must for fast

and efficient operations, as no tug boat and/or mooring system will be deployed. The vessel is equipped with the

latest development of the GustoMSC continuous cylinder jacking system. Tis pin-in-hole system operates with four jacks per leg, of which three systems are engaged (elevating or lowering) while one system is in the recycle mode. Tis jacking system realizes a liſting speed of 29m/hr at maximum elevated weight. Leg handling speed is up to 40m/hr. After touchdown of the legs, the

preloading operation takes place to secure the vessel. Te advantage of the four-legged unit is the fast diagonal preloading. In elevated condition, and with full variable load, the vessel can withstand the year-round survival conditions of 10.8m significant waves, 41m/s wind and 1.25m/s current at a maximum water depth of 45m. The accommodation deckhouse is

situated at the forward end of the vessel, while the engine rooms are located in the ship’s center – away from the accommodation spaces. Te vessel is powered by four diesel

generator sets of 4300kW each. Te diesel- electric system is powering the 6.6kV main bush bars. Te thrusters, hydraulic power units (HPUs) and main crane are powered through the 690V switchboards. Te 440V and 220V switchboards complete the electric system. Te ‘wrap around the leg’ column crane

is the answer for efficient installation liſts and freeing the deck for storage of wind

NG-9000C ordered by Fred. Olsen Windcarrier at Lamprell Shipyard in Dubai (Credit: GustoMSC/ Fred.Olsen Windcarrier/ Lamprell Shipyard).

turbine modules. When locating the crane at the edge of the free deck area, the deck area served by the crane hook is maximised. Positioning the crane close to the side of the jack-up is where the crane outreach is most effectively used. However, the obstruction of the work space by the nearby legs is still present. When observing this, the easy assumption is to arrange the crane around one of the jack-up legs. Te principle of this arrangement is not

new. In 1968 a jack-up, “Cowrie One”, was built at the Gusto Shipyard with a small crane built around the leg. However, the present specification of the crane around the jack-up leg (800tonnes at 24m outreach) is much more ambitious than this example from the past.

New challenges

As GustoMSC currently has an order portfolio of cranes in the range of 500 to 5000tonnes lifting capacity, its development work is more oriented towards a proper combination of proven components into a new crane concept than in using novel technology to meet design criteria. GustoMSC’s column cranes in this range

are located on an individual pedestal, and supported by an integrated 3-race roller bearing or a king-post bearing combined with horizontal bearings at two elevations. Its large offshore cranes with a liſting

capacity of 4000 to 5000tonnes 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 latest development regarding

the GustoMSC “wrap around the leg” crane utilises suitable components from the described crane concepts. Since the jack-up leg penetrates the centre of the crane, the bogie-wheel bearing system was selected. 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. Te fitting of individual bogie-sets to compose the bearing system also very conveniently decouples the construction of crane and jack-up leg. OMT

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