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/ 07 Feb, 2023
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Big step towards large scale installation

Anticipating upcoming large-scale floating windfarm installation, Damen has developed the FLOW-SV vessel concept that is set to accelerate the growth of this new maritime segment. The Damen FLOW-SV is specifically designed to install ground tackle for floating offshore turbines.

Measuring approximately 150 metres in length with a 32-metre beam, the FLOW-SV is a big ship. The vessel is able to transport the immense lengths of chain needed to install and secure 9 anchors or suction piles so, instead of anchoring only one floating turbine per mission, the vessel can carry enough equipment to fit out three turbines. It is also powerful enough to carry out sufficient proof loading on the anchors, making installation more efficient still.

Damen engineers researched the amount of gear that the FLOW-SV needs to take onboard to be able to install three floating turbines in a base case of 100 metres water depth, their calculations added up to five kilometres of chain (chain links of 152 mm diameter) 4.5 kilometres of fibre rope of 112 mm diameter, 9 anchors each weighing 15 tons and almost 100 clump weights of 10 tons each, D-shackles, tensioners, as well as steel cable. The FLOW-SV is designed therefore to carry a load in excess of 4,000 tons. Depending on seabed conditions, depth and windfarm operator requirements, anchors can be replaced with suction piles to provide a secure ground tackle.

A unique feature of the FLOW-SV is the combination of bollard pull generated by the thrusters and added pulling force from the bow reaction anchor winch. The FLOW-SV deploys the bow anchor and embeds it by reversed bollard pull. She then moves to the spot where the anchor for the floater needs to be installed. After letting out enough chain length, the anchor needs to be proof loaded, ensuring a secure seabed connection. Using the four thrusters, FLOW-SV has 400 tons of bollard pull. Pulling strength is enhanced by the forward anchor handling winch that generates another 600 tons. This adds up to approximately 1,000 tons of proof-load that then acts on the turbine floater anchor.

To survey and find the best spot to install the anchors, the FLOW-SV has two working class ROVs (Remote Operated Vehicle) with two separate control rooms next to a moonpool (an opening to launch submarine vehicles in the middle of the vessel).  The ROVs can be deployed post-installation to inspect  the anchor and confirm it has dug in sufficiently to provide secure ground connection.

The FLOW-SV is fitted out for renewable fuel Methanol. Six generators feed electric thrusters. When the floater anchors are being secured and maximum bollard pull is required, the two fixed 5.5 metres propellers in nozzles are engaged. Transit journeys will use the azimuthing 4.5-metre propeller size thrusters to propel the vessel, eliminating the need for rudders. 

“With the FLOW-SV, we have developed a vessel which covers the entire process of attaching mooring lines. This vessel, combining the supply, installation, securing and inspection of the ground tackles for floating turbines in one vessel, introduces a big step forward towards large scale installation of floating windfarms. The concept reflects our expertise in operational demands and efficiency,” says Wijtze van der Leij – Sales Manager. “At the moment, we are still in the concept phase. But we are now entering a stage where we would like to partner up to refine and customise this concept. Together with a launching customer, we aspire to accelerate the floating offshore windfarm installation industry.”

Exhibitor; Damen Shipyards
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