Two Dutch companies, SeaOwls BV and Ulstein Design & Solutions BV, have developed a new lifting vessel for the offshore wind industry. The ship design is called the SOUL and is a real game changer, according to the developers.
The patented design of the SOUL (the name is a combination of SeaOwls and Ulstein) will allow energy companies to install larger and more efficient wind turbines at sea.
Ulstein has been involved in ship designs for the offshore wind industry for many years and saw that the existing lifting vessels for installing wind turbines were at the limit of what was economically feasible. Cost-effectiveness was therefore hardly achievable anymore. From the market, including turbine suppliers, energy companies and contractors, there was an increasing demand for further cost-effectiveness through economies of scale.
Square table
Ulstein and SeaOwls pooled their knowledge and looked at what would be the most ideal lifting vessel to realise this. What came out of that was a 'large square table with the legs as far into the corner as possible'. Technically, however, this is not possible; a square does not sail nicely through the water. So the companies had the 'table' rotated 45 degrees to create a natural bow shape for a self-propelled vessel, a kind of lozenge.
A seemingly simple modification, but one that brings many operational and cost benefits. "Looking at the market, we saw that the current crane-lifting vessels were starting to reach their limit in terms of size," explains Ulstein's Nick Wessels. "The limit now is installing wind turbines of 6 to 8 megawatts. We looked closely at the ratio between what a ship can carry in cargo and what it has to hoist up in its own weight to land on its legs. The lighter the ship is relative to what it can carry in cargo, the better. By using a cross-shaped structural main frame, the design is more than 10% lighter than existing lifting vessels, while the payload capacity is greater. Also due to the large lifting crane, this vessel can install wind turbines of 10 to 12 MW. Because the legs are on the centreline, you can do nice things with the crane. We came up with a structurally different solution that allowed us to save weight but distribute forces better."
Existing manufacturing technologies
No new production technologies have been used for the new lifting vessel, Wessels said. "Everything in the SOUL is existing. The hull is bigger but it already exists. Internally, ordinary welding has been used, there are straight beams in it. Even the lifting mechanism is not new. But the combination of how everything is applied together is new. In particular, the structural head dressing and the shape are innovative."
The first potential customers who have had a preview of the lifting vessel are responding positively. "The only comment we have received is about the width of the vessel. We have now chosen the largest unit, but the captains who have sailed with it have expressed that they can get it into the ports where they need to be. We think the SOUL can really take the industry forward again."
Thanks to the ship's size, the design could contribute to subsidy-free wind energy, Ulstein previously stated. "In the offshore wind market, everything is focused on cost reduction and price per kilowatt hour. If you can achieve the power with two wind turbines where three are needed now, that has a huge impact." He expects the "new generation of wind turbines to enter the market by 2020.
The SOUL design series will have different sizes to transport and place 3 to 6 wind turbines of 10-12MW each.
Photos: Ulstein Design & Solutions BV
By: Kelly Bakker
