The innovative offshore floating Hywind wind turbine, moored in the North Sea off the Norwegian coast, demonstrates how Trelleborg Offshore’s syntactic foam buoyes contributes to the future of offshore power generation. “People see the tower and turbine, but forget that the expertise in designing the subsea portion is also critical, because it keeps the whole turbine afloat,” says Gary Howland, the company’s Renewables Sales Manager. “The dynamic floating structure weighs 5,300 tons and measures 165-m tall. A full 65m floats above the sea surface. The 13 km power offtake and communications cabling attached to the structure further adds to its weight.
“This subsea technology is already proven. The Distributed Buoyancy Modules (DBMs) developed for deepwater support of umbilicals and risers in the oil and gas industry are ideal for this application becuause they help reduce project risk using proven technology.
“It’s like an iceberg; the mass floating below the surface ensures stability. Unless the weight is supported by properly designed buoyancy the whole structure would be much less able to resist the extremes of the offshore environment and the cable could suffer premature damage,” says Howland.
For Hywind, Trelleborg Offshore designed and supplied 45 polymer-coated syntactic foam DBMs which provide buoyancy support for a 3 ton, 100-m section of cable as it exits the turbine spar and descends to the sea bed at 220m below the surface. The buoyancy modules include an internal clamp for secure fastening and precise positioning on the cable.
“For best buoyancy under different sea conditions, engineers calculated the position of the buoyancy modules on the cable. The positions must be maintained, despite stresses during launch and in operation. The clamp is crucial. Its design, material selection, and manufacturing technique are critical ensuring the finished clamp maintains the buoyancy module position, during cable contraction and expansion, over the 20 year lifetime of the project.
“Trelleborg Offshore has substantial expertise operating in deep water and subsea environments, and a track record acknowledged by many offshore engineering companies. The company also has experience with DBMs and says more than 35,000 modules are in service.
“We have seen many of the technical challenges before, in the offshore oil & gas arena, so our engineers can quickly and easily adapt proven solutions for use in offshore wind-power generation. This will greatly reduce project risk and let industry develop quicker and at less cost.”
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