Working closely with contractor GeoSea, The Netherlands-based Temporary Works Design has developed the design of a new type of ‘mini jacket’ foundation that it believes has a number of advantages compared with monopiles and conventional jackets
The mini jacket foundation is not a new idea, but it could have new applications in the offshore wind industry, says Dutch company Temporary Works Design (TWD), which has been exploring the application of the concept with installation contractor GeoSea.
Simon Lembrechts, who works in business development at TWD, told OWJ he believes the concept has a number of potential advantages for offshore wind turbines. He noted that the size and weight of monopile foundations has been growing to the point where they exceed the capacity of some installation vessels. Jackets are an alternative to monopiles, but the complexity of jacket fabrication can result in high foundation costs.
TWD foresees an installation process for the mini jacket that starts with the mini jacket acting as the template, hanging from a jack-up barge and used as a piling template. Lightweight, inclined piles are driven through the sleeves of the mini jacket, and the piles are connected to the sleeves by a swaged connection. Once piling has been completed and piles connected, the mini jacket forms a permanent interface with the tower.
“One of the biggest advantages of this concept is that you can use a single vessel for installation,” said Mr Lembrechts. “On one campaign, with no pre-piling, you can use smaller jack-up barges of which there is a large fleet available. It also means that a jack-up can carry more foundations per trip, because the components can be easily stacked on board. Another advantage is that the mini jacket concept weighs less than monopiles.
“Overall,” he explained, “the concept is much less complex than a conventional jacket. Smaller components mean it is easier to fabricate, and more fabricators are available that can construct it. Smaller components also simplify supply scenarios. The mini jacket is easier to store, and requirements for load-out quays are simplified.”
Another big advantage of the concept is that installation costs are significantly reduced by as much as 30–40 per cent. The company believes that, as the water depths in which wind turbines are installed, the distance from land over which the jackets have to be transported and the size of turbines all increase, the advantages of the mini jacket concept also increase.