Weighing 960 tons, measuring 26 meters in width and 30 meters in height, the new A-Frame would increase the total height of the Svanen to 125 meters.
With few cranes in the world capable of the lift at the 65-meter height to clear the vessel’s deck, the PTC ring crane was perfect for the job – it allowed the frame to be prefabricated and lifted as a complete unit.
This not only allowed for safer assembly of the A-Frame, but dramatically reduced the downtime of the offshore wind vessel. A project that could take a year was completed in a few months and the heavy lift was executed in just one week, thanks to close collaboration between Mammoet and Van Oord.
Dual scope: heavy lifting and site transport
Mammoet was approached to support with two elements of the project. The first was the transportation and lifting of the three key components that made up the A-Frame.
These were fabricated by Holland Shipyards at two separate warehouses near Rotterdam, before being shipped by inland vessels to Mammoet’s quayside headquarters in Schiedam.
Once in Schiedam, the A-Frame was offloaded onto Mammoet Self-Propelled Modular Transporters (SPMTs) and moved to a laydown area.
For this whole phase, a combination of gantry masts, crawler cranes, a 250-tonne harbor crane and floating sheerlegs were utilized.
The second stage was the main PTC hoist. This saw the assembled A-Frame driven 66 meters using 64 axle lines of SPMT trailer and parked on a temporary support, ready for the PTC to perform the hoist.
The configuration of the PTC ring crane to perform the lift was 107 meters of main boom, 67 meters of luffing jib, and more than 4,000 tons of counterweight.
Weighing up the challenge
The biggest challenge for the engineering team was establishing how different parts fabricated at two separate locations would behave as an integrated component.
It wasn’t possible to precisely know its final weight, nor its exact center of gravity. Julian Alkemade, Project Manager at Mammoet, explains:
“We were able to estimate a certain weight before putting it on a vessel and shipping it to Schiedam for final assembly, but you always have the issue that if you combine those parts together, weld them together, bolt them together, you are unsure of what the exact weight will be. There is always deviation within a certain percentage.”
Because of this, the team performed a weighing operation on the A-Frame once it was assembled. They also planned two separate rigging configurations, with the direction to be taken resting on the results of the weighing.
“Between the hook of the crane and the A-Frame itself there is a lot of steel, shackles and grommets, so we had two plans,” adds Alkemade. “The weighing campaign was a very important, and integral, part of the process. It determined whether we used longer/shorter grommets, larger/smaller shackles, or changed the lifting eyes.”
Right ring crane, right place
Installation of the A-Frame took just one week. The efficiency of this offshore wind energy project was due to Mammoet’s close relationship with the customer facilitating easy access to the crane, and the fact the PTC ring crane made it possible for the frame to be installed in a single heavy lift. It enabled a safer and more efficient plug-and-play solution.
“We are currently supporting Van Oord with a number of developments in the offshore wind power sector to support the efficient handling of monopiles”, said Remco Zandstra, Commercial Manager at Mammoet.
“By engaging early during the project, we were able to ensure the right equipment was reserved for this unique project. We are proud to support Van Oord’s impressive ambitions within the wider energy transition.”
