Wind development requires new vessels based on offshore oil technology

Above, a crane barge upends the floating tower for Statoil Hywind’s deepwater wind turbine project off Norway in May 2009. (Courtesy Statoil Hywind/Philip Tornes)

For hard-core oil men and alternative-energy skeptics, it may seem like a plan soaked in irony: As wind turbines are placed along the U.S. coastline, the wind-power industry intends to adapt technology from the offshore petroleum community to install and service the equipment.

That means flotillas of heavy lift boats, crane barges, service vessels and crew boats that are a familiar sight in the Gulf of Mexico soon may visit areas such as the Gulf of Maine, New Jersey Shore and Lake Ontario. The vessels will embed platforms into the seabed and place turbines on top of them. Cable-laying ships won’t be far behind.

The Bush administration, in a plan endorsed by the Obama administration, called for the nation to generate 20 percent of its electricity from wind by 2030. While land-based wind farms likely would generate most of that power, the government wants 54 gigawatts to come from offshore systems.

Shallow-water wind initiatives are in the works off the coast of at least nine U.S. states — Massachusetts, Rhode Island, New York, New Jersey, Delaware, Georgia, Ohio and Texas, plus a proposal for Lake Michigan. In addition, Maine recently announced three sites for seaworthiness experiments on various designs for floating deepwater wind projects.

In the beginning, the wind pioneers plan to hire existing jack-up boats and crane barges to deploy the equipment at sea. As the offshore wind industry scales up, however, energy executives say purpose-built vessels will be needed to ensure that the repetitive work is carried out efficiently and safely.

“We’re borrowing from those offshore oil systems and adapting them to put wind turbines on top of them,” said offshore wind researcher Habib Dagher, director of the Advanced Structures and Composites Center at the University of Maine. “As they get bigger, you’re going to need bigger vessels to get them out there.”

Typical offshore wind turbines on the job now in Europe generate 5 MW each. Their hubs are 300 feet above the waterline, with 200-foot-long blades — for a total diameter of 400 feet.

The United State’s current inventory of heavy-lift vessels does have the capacity to handle such loads for small-scale projects on a spot basis, said Charles Nordstrom, a naval architect with The Glosten Associates in Seattle. “There are a handful of existing lift boats that can do the job,” said Nordstrom. “It’s not ideal, and the industry will need purpose-built Jones Act-compliant vessels.”

The latest proposed designs, including one project in the United Kingdom, envision larger turbines that churn out 10 MW. They would be 584 feet in diameter and they’d weigh 200 tons apiece, requiring sturdier poles, which the industry calls “monopiles.” An assembly-line-type operation would install as many as 100 units per facility.

Such massive windmills would require an 800-ton crane, versus the 200- to 400-ton capacity cranes common in the Gulf of Mexico oil region, said Kevin Pearce, director of marine engineering and offshore operations with developer NRG Bluewater Wind. For cost-effectiveness, it’s also crucial that vessels be stout enough to carry multiple turbine units and that installation work be able to continue in seas of up to 7 feet to minimize downtime.

“The monopiles, as they get longer, they get heavier,” Pearce said. “We need to be able to lift the foundations in one piece and not in sections. The existing oil and gas inventory that I’ve seen doesn’t have the decking capacity or the jacking capacity to lift the components.”

Bluewater Wind intends to construct three wind turbine installation vessels at Aker Philadelphia Shipyard. The total project cost is $450 million. The deal hinges on the Philadelphia Regional Port Authority winning a $135 million grant from the U.S. Department of Energy. Bluewater Wind would raise the remaining $315 million in private equity. The grant announcement is scheduled for early 2010.

Glosten Associates is a participant in a separate plan to construct similar vessels at the Keppel AmFELS shipyard in Brownsville, Texas. That group is trying to raise all of the investment money privately and plans to start with just one boat. The vessel would be purpose-built for transporting and installing wind turbines, plus conducting major maintenance and repairs. Code-named the KATI, it is designed to be able to transport three 5-MW wind units at a time and install them in water as deep as 200 feet.

If the federal government’s goals are to be met, the industry would need 16 purpose-built installation vessels just for the East Coast, Bluewater Wind said.

In addition, specially made crew boats would be needed to conduct regularly scheduled maintenance on the turbines. Again, minimizing downtime and maximizing safety in heavy seas would be paramount, said Nordstrom.

“The challenge is the relative motion between the boat and the fixed tower,” Nordstrom said. “In rough weather, the relative motion becomes larger and it becomes unsafe to transport people from the boat to the tower. You don’t typically have the ability to hoist, because you’re boarding a tower that is unmanned.”

European wind producers have begun working with Small Waterplane Area Twin Hull (SWATH) vessels as the crew boat of choice. A SWATH vessel is similar to a catamaran, except both hulls are submerged.

“It’s a hull form that minimizes motion,” Nordstrom said. “There is a piece of equipment on the boat that has motion compensation capabilities — sort of a bridge between the boat and the tower.”

The industry participants say they are committed to adhering to Jones Act rules in the design, construction, crewing and operation of the wind-energy service ships and boats.

“We’re going to build vessels in the U.S.,” Bluewater Wind President Peter Mandelstam said. “We very strongly believe that the Jones Act is important … union jobs in U.S. shipyards.”

Initial U.S. offshore wind projects — probably off Delaware and New Jersey — will be the shallow-water variety, defined as zero to 100 feet of water. Most shallow-water turbines are installed on monopiles driven into the seabed or on shallow gravity units that are filled with ballast and rest on the ocean floor.

In so-called “transitional” waters of 100 to 200 feet, Europeans are using tripod pilings with water-driven suction buckets or four-sided jacket designs.

Dagher, at the University of Maine, said the greatest potential is in deepwater areas of 200-plus feet, where winds tend to be stronger and steadier. At 10 to 20 miles off the coast, deepwater is also politically more palatable, because coastal residents wouldn’t be able to hear the turbines or see them on the horizon. Wind resources are considered “outstanding” or “superb” along most of the nation’s northeast and northwest coasts and in the Great Lakes.

The deepwater projects require windmills that float instead of being driven into the seabed. Worldwide, only one full-size system exists thus far. In the summer of 2009, energy company StatoilHydro installed a floating wind turbine in 400 feet of water off Norway. It will undergo two years of tests.

In the United States, using part of an $8 million Department of Energy grant, Dagher’s institute is evaluating at least three designs to determine their buoyancy and seaworthiness and how the spinning turbines might impact the floating systems.

Statoil Hywind, as the Norwegian project is called, uses a Technip-built “ballast-stabilized” spar buoy system, with three catenary lines attached to the ocean bottom with drag-embedded anchors. Other experimental concepts include a vertical “mooring-line-stabilized” method with pin pile anchors and a “buoyancy-stabilized” barge with catenary mooring lines that curve inward from a wider base.

In December 2009, the state of Maine and DeepCwind Deepwater Offshore Wind Consortium announced three sites in the Gulf of Maine where small-scale trials will take place. Dagher expects to install the demonstration turbines by 2011.

The logistical needs of the deepwater units may differ depending on the size and design. StatoilHydro constructed its components in sheltered water, towed them to the field, upended the huge tube and assembled the segments. Vessels included tugboats, a crane barge and a self-unloading bulker to add the solid ballast, plus a cable-laying vessel.

Norwegian maritime-academy students conceived the WindFlip — a wind-turbine-transport barge that uses ballast and air compression to rotate the entire vessel and cargo 90° to a vertical position.

Also in December, the New York Power Authority called for bids to develop the Great Lakes Offshore Wind Project, which would install turbines in Lake Ontario, Lake Erie or both. Vessels traveling through the Great Lakes-St. Lawrence Seaway are limited to a beam of no more than 78 feet, so yet another set of vessels may be developed to specialize in freshwater work, Bluewater Wind’s Mandelstam said.

By Professional Mariner Staff