Jack-up vessels have long been the vessel of choice for turbine installation, but larger, heavier turbines have prompted a rethink and a number of new designs
Over the last decade, self-propelled jack-ups have evolved into autonomous platforms able to carry turbine components on deck, position themselves using dynamic positioning (DP) and provide a stable working platform on a robust jacking system designed for frequent operations. Combined with a dedicated crane, these features have enabled them to safely install the latest generation of 6–8 megawatt (MW) turbines.
Over time, the design and operation of units such as these has evolved in the direction of process optimisation, in which the main focus has been on minimising installation time per turbine, thus enabling faster overall field development.
However, the trend towards larger turbines exceeding the 6–8 MW size range has presented new challenges, such as a requirement for increased lifting height, the ability to lift heavier loads and increased crane reach. This trend has also increased focus on the issues related to the dynamics between the turbine and the installation vessel.
The latest generation of installation vessels can be enhanced and upgraded, but the industry has come to realise that a new generation of vessels will ultimately be required for 8–10+ MW turbines. Bigger is almost always better as far as installation vessels are concerned, but greater operational flexibility is also required.
Responding to some of the above-mentioned requirements, GustoMSC has unveiled a new turbine/foundation vessel, the NG-20000X, which is characterised by a high variable load and the ability to install in deep water. Equipped with the GustoMSC integrated telescopic leg crane, the NG-20000X can install heavy foundations, and when the boom is fully extended, it reaches adequate lifting height and capacity to install future generation wind turbine components, the company said.
“A different approach is required for the future turbines with capacities beyond 10 MW,” said GustoMSC of the new jack-up unit, noting that it enjoys the advantages of the proven VSD jacking system and a large unobstructed deck area. “The variable load capacity of 16,500 tonnes enables contractors to make a round trip carrying six complete sets of wind turbine components with a turbine weight of 1,000 tonnes or carry seven 900-tonne jacket foundations, optimising the cost per installed turbine or foundation,” said the company. “A key feature of the design is the innovative combination of high hoisting height for wind turbine installation and heavy load capability for foundation installation.”
To combine these two requirements, GustoMSC has developed a telescopic leg crane. “By introducing a telescopic boom that features a very high hook height when extended (1,250 tonnes at 160 m) and increased hoisting capacity when retracted (2,500 tonnes at 120 m), it is possible to break the cycle of extremely long booms and increasing crane weights, resulting in a more economic crane design and increased variable load available for operations,” GustoMSC said.
GustoMSC has also proposed using liquefied natural gas (LNG) as a fuel for new-generation vessels but not just to reduce emissions. It also believes that, apart from the environmental benefits of LNG-fuelled ships, closely matching the LNG propulsion system to the operational profile of a vessel can provide a significant reduction in capex.
“A capex-optimised design approach further enhances the business case for an LNG-fuelled installation vessel,” the company claims. “Optimising the LNG capacity installed to the long-term average operational profile is a very effective way of reducing the capex.”
As highlighted previously in OWJ, a number of companies have ordered vessels targeting the growing market for ships capable of decommissioning offshore oil and gas platforms and installing jacket foundations for offshore wind turbines. Among the forthcoming newbuilds targeting the decommissioning and offshore wind markets are Orion, DEME’s new vessel, and Bokalift 1, based on an existing semi-submersible heavy-lift ship that the Dutch company is converting into a 3,000-tonne crane ship.
The new vessel for Boskalis will combine the 3,000-tonne lifting capacity revolving crane with a deck area of 165 m x 43 m and a DP2 positioning capability. Like Orion, it will be used to install jackets and monopiles for offshore wind turbines and to remove obsolete oil and gas platforms and transport. Boskalis says it could also be used to transport and install certain types of newbuild oil and gas production platforms. Having DP2 will mean that the vessel will not rely on the installation of an anchor spread. The vessel will have accommodation for 149 people and a helicopter deck for offshore transfers. Delivery is expected at the beginning of 2018. A sister vessel is also scheduled for conversion into another 3,000-tonne capacity crane vessel.
Bokalift 1 will be capable of lifting 3,000 tonnes at a radius of 28 m and 1,200 tonnes at 50 m. The load a heavy-lift crane can lift is important, but so too is the height to which it can lift a load. Using its main block, the crane on the vessel, which is being built by Huisman, will be capable of lifting a load to 90 m above deck at a radius of 30 m and 99 m at a 35 m radius.
The 216 m long vessel has a breadth of 43 m, moulded draught of 13 m and operating draught of approximately 8.5 m. The deck will be strengthened to 25 tonnes/m2. The machinery takes the form of four 3,840 kW Wärtsilä engines and two 4,800 kW Bergen engines with a 1,110 kW auxiliary engine from Wärtsilä. Bokalift 1 will have a ballast capacity of 2 x 1,500 m3/hr and an anti-heeling system with a capacity of 8 x 2,000 m3/hr. The vessel will have a transit speed of 14 knots.
In foundation installation mode for the offshore wind market, the vessel would load itself with jack or other types of foundation using its crane and, having arrived at the location of the windfarm, would lift the foundations and stab them into place on pre-installed pin piles using the crane whilst in DP mode.
New types of jack-up vessels have also recently been proposed, among them one from SeaOwls and Ulstein. The SOUL (after SeaOwls and Ulstein) heavy-lift jack-up was unveiled at the OWJ conference in London in February this year.
The companies say the cruciform structural layout of the jack-up makes the patent-pending solution more than 10% lighter than conventional jack-up vessels. “In combination with a high-capacity crane, SOUL enables operators to take the next step in developing offshore windfarms,” they said. The concept was developed with the installation of next-generation wind turbines in the 10–12 MW class in mind but is also suitable for installing 6–8 MW units.
“The development of this novel jack-up vessel is the logical next step in our strategy to broaden our portfolio and support the offshore wind industry with more efficient assets,” said Ulstein Group deputy chief executive Tore Ulstein. “Combining the track record in heavy-lift vessel designs from Ulstein in the Netherlands and SeaOwls’ experience in jack-up technology has resulted in an innovative jack-up vessel concept based on proven technology.”
The companies notes that scaling up conventional heavy-lift jack-up vessel designs is challenging due to the disproportional weight increase compared to gain in variable deck load but believe that their design overcomes this problem.
“We noticed this created uncertainty among turbine manufacturers, windfarm operators and installation contractors about how to install larger turbines,” said Erik Snijders, founder and managing director at Rotterdam-based SeaOwls. “So we went back to the optimal jack-up design, a square platform with the legs spaced out as far as possible. Rotating the platform by 45 degrees provided a natural bow shape with two legs and the crane on the vessel’s centreline.”
“This seemingly simple twist in the design allowed us to make a huge improvement in operations,” said Ulstein Design & Solutions BV deputy managing director Bram Lambregts. “With the main crane around the stern leg, optimal main deck reach and over-the-side lifting capabilities is created, and as the hull now houses much larger leg footings, bearing pressures on the seabed are reduced, while the wake of the spudcans does not interfere with the inflow to the propulsion thrusters.”
The SOUL series will be available in various sizes, allowing the transport of three to six 10–12 MW turbines. All loading and installation operations can be performed without the need for ballast water.