A Modulift spreader was combined with a 45-meter-long beam attached to a gantry and a crawler crane in order to tandem lift 760-metric-ton monopiles from pontoons onto land in Cuxhaven on Germany’s North Sea coast.
Schmidbauer GmbH & Co. KG was challenged by Cuxport GmbH to develop a solution for lifting the monopiles bound for the Nordsee One offshore wind farm, using an existing gantry. However, the crane only offered 600 metric tons of lifting capacity, and the beam itself had a net weight of 100 metric tons, which meant the gantry was only suitable for 500 metric tons of lift.
Consideration also had to be given to a number of additional complications. There was a special coating on the monopoles, so attaching rigging equipment at all points wasn’t possible. Height was limited, and there were 20 meters between the gantry’s hooks positioned 10 meters to each side of the center.
The lift planning team discovered there were two lifting lugs in the center of the 45-meter beam offering a more convenient distance of just 4.75 meters. However, Philipp Verges, sales manager for global projects and key account manager offshore at Schmidbauer, said they were 90 degrees in the wrong direction. The beam was originally manufactured for special lifting of three-legged tripiles, so the forces applied during lifting would have broken the eye plates.
Eventually, a MOD 400/600 beam, sourced from Schmidbauer stock, was used as an inverted spreader, owing to the two pick points above it and the need to bring the slings together in one point. MOD 400/600s offer capacity to 600 metric tons from 12 meters (40 feet) up to 23 meters (76 feet) at lower capacity.
“Slings came together in a 600 (metric ton) hook block that allowed us to complete turning of the monopiles,” Verges said. “The rigging around the monopiles had to be kept short, so we had to deliver (125 metric ton) Polytex slings at a special length to fulfill the requirements.”
At the other end of the tandem lift, Schmidbauer provided a Liebherr crawler crane (model LR 1600/2) with wheeled counterweight carrier that allowed it to lift even the second row of each pontoon load from the barge without turning it.
Thirty monopiles were lifted in a five-month period. Two traveled on each pontoon to Ambau GmbH in Germany. Verges said if a smaller crawler crane was used, after picking up the first row, Schmidbauer would have had to turn the barge prior to lifting the second unit. Otherwise, the distance would be too far.
The Nordsee One wind farm has one offshore substation platform and 54 wind turbines to be installed in water depths between 25 meters and 29 meters. The wind farm is in a special spatial planning area reserved for offshore wind energy.
For more information, go to www.modulift.com