Crane handling and SPMT reduces downtime in TP loading

22 kilometres off the coast of Scotland, Moray West marks the third offshore wind farm in the Moray Firth region, joining Moray East and Beatrice. The clean energy project will help deliver low-cost, low-carbon electricity to 1.33 million homes.

With a track record of working together, Global Energy Group trusted Mammoet’s management and engineering when the planned roll-on-roll-off (RoRo) method of offloading drilling platforms proved unfeasible.

Mammoet proposed to transfer the TP onto self-propelled modular transporters (SPMTs) using a crawler crane, the ballast of which is supported by a separate combination of axle lines. This method provided greater maneuverability and less downtime between lifts. It also prevented the changing tides in the marshalling port from affecting the operation.

Mammoet’s scope of work for this clean energy project included receiving the components at the Port of Nigg after being transported by sea, unloading them onto SPMT trailers and then transporting them to a temporary storage area where preparations for assembly could be carried out.

Once the TPs are ready for delivery to sea, they will be transported back to the quay by the SPMT vessel in batches of four, from where they will be picked up and delivered to the offshore wind farm site by an installation vessel.

The original plan was to remove TP from the ships using an SPMT with a TP handling attachment. However, this plan had to be changed late in the planning process.

“As the situation evolved, new information about the stowage plans, how the TP would be stowed on the supply vessel and the heights and methods of mooring meant that this was no longer an option,” says Oliver Smith, Senior Commercial Manager at Mammoet. “It came down to the loading and unloading methodologies not being compatible, and a big part of that was the fact that the vessel had to be moored stern to the quay. This meant there wasn’t enough space to get the TP crew on board and off the TP. We were able to provide solutions to change the design of the scaffold to enable it to operate, but ultimately, to support a holistic approach to moving components from A to B, we developed a crawler crane solution.”

There were two types of TP: 60 units weighing approximately 505 tonnes, designed to support offshore wind turbines, and two heavier offshore substation platform (OSP) transition elements weighing approximately 832 tonnes.

The 60 TP were lifted from the vessel by a LR11350 crawler crane on a 32-lane SPMT configuration. The crane was supported by a separate 24-axle combination that was used to manoeuvre the ballast tray.

“You can crane the tray, but we needed a faster, more efficient mechanism, so we used the SPMT,” added Mr Smith. “If you crane the tray and you have close to 600 tonnes of ballast, you have to lift that block by block to move it. With the SPMT, once it takes on the ballast car load, it can move faster.”

TPs arrived at the port in varying numbers, in batches ranging from 4 to as many as 16. This sometimes created challenges, especially if the vessels had to make the long journey from the UAE to the UK via the Suez Canal and there were any delays in between.

Similar to when the team first developed a lifting solution using SPMT and a crawler crane, when plans changed, this time they were able to adapt, manage and prevent issues resulting from schedule changes.

The crane solution also meant that the unloading stage was not adversely affected by tides as the components were lifted off the vessel rather than being pushed off it.

Mammoet’s strong partnership with the customer is based on many years of trust. The company has successfully completed several heavy lifting and transport projects at the same location, including for the Seagreen Offshore Wind Farm.

“Our partnership is based on many years of trust, having completed previous successful heavy lifting and transport projects at the same site, including the Seagreen Offshore Wind Farm,” said Mr Smith. “We have a good working relationship with the port and have been able to work together in a very complementary way. Because we have such good experiences with each other, we can work well as a team to deliver projects safely and efficiently, and ultimately give the end customer the benefit of that good working relationship. I think its success was a testament to the start of the project, when we worked closely together and provided transparent feedback from the engineers, which enabled us to change our planning at the last minute to use the crane and complete the project on a faster schedule.”

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Giant Squirrel

Global Energy Group