Sector:
Offshore Wind
Expertise:
Load-in & load-out
Heavy transport
Benefits:
Optimized schedule
Parallel operations
Location:
Netherlands
More efficient load-in phase results in fewer transcontinental sea voyages.
Mammoet is playing a key role in the lifting and movement of next generation wind turbine components for the world’s biggest offshore wind farm projects.
In 2023, it was selected by Buss Ports to marshal foundations for two of the largest offshore wind projects in Europe - Nordseecluster A (Germany) and Thor (Denmark).
Nordseecluster (A & B) and Thor are joint offshore wind projects of RWE (51%) and Norges Bank Investment Management (49%). These offshore wind projects will play a crucial role in their countries’ green energy targets. Combined, they will achieve a total planned capacity of up to 2.6 GW.
Mammoet’s scope was to manage the phased load-in, temporary storage and load-out of 116 XL monopile foundations for both wind farms at Buss Terminal Eemshaven in the Netherlands.
With different specifications of monopiles being shipped to the port in different numbers, the load-ins had to be carefully planned so that marshalling equipment was configured in advance and space at the port could be managed effectively.
Adding further complexity was the limited ground bearing capacity of the quay, an unusual shipping configuration and the fast-changing tides - all of which required creative engineering to manage.
Mammoet not only marshalled the monopiles for both projects safely and efficiently, but it was also instrumental in supporting Buss to reduce the total number of load-ins, saving on several 60-day global sea voyages.
Saddling up for 116 XL monopile load-ins
Preliminary engineering work began in September 2023, with Mammoet carrying out a feasibility check using its XXL monopile transport system as a basis.
Buss has developed its own saddle system for large monopiles and wanted to put it to work on this project with Mammoet’s Self-Propelled Modular Transporters (SPMTs).
Engineers at Mammoet worked with Buss to ensure its saddle system was compatible with the SPMTs – chiefly, that its cylinders and hoses would connect to the transporter’s hydraulic system.
The monopiles for Nordseecluster A weighed around 1,500 tonnes and measured on average85 meters in length; the foundations for Thor stretched approx. 100 meters and weighed around 1,500t. The XL monopiles were offloaded onto the quay using a RoRo linkspan ramp and transported using 80 axle lines of SPMT fitted with the Buss saddles.
Monopiles are normally transported in a longitudinal configuration. However, to deliver more units per voyage they were loaded in a transverse orientation and protruded slightly over the side of the vessel.
To support this, Mammoet needed to unload these structures ‘sideways’. This methodology also allowed the load-out method from China to be reversed.
Due to the low ground bearing capacity of the quay, an unusually long linkspan ramp was used. Typically, linkspans measure five meters – this ramp stretched around 12 meters before touching down on the quay.
As the monopiles hung over the vessel’s edge, during load out of the first foundation three axle lines of SPMT rested on the linkspan ramp rather than the deck.
With the ramp around 400mm higher than the deck of the vessel, the team would have had to use less packing on only these three axle lines, so they could fit beneath the first monopile.
This, in turn, would have added considerable time to the load-ins, with the SPMTs and saddles needing to be reconfigured between the first and second monopile lift.
It also would have meant there would only be enough time to offload one monopile in the first tidal window. An alternative solution had to be found.
Gaining height, time and savings
“To overcome this, we placed wooden mats on the deck of the vessel to gain the height we needed,” explains Wouter Santen, Project Manager at Mammoet.
“This was done during a non-critical path outside of the tidal constraints. This approach avoided the need to reconfigure the SPMT between the first and second monopile lifts, allowing us enough time to offload two monopiles instead of one.”
To ensure the tidal constraints were comfortably met, the monopiles were offloaded with their sea grillages still attached, allowing the SPMTs to disembark quicker.
Once the components were on the quayside, the grillages were removed using additional SPMTs. The monopiles were then driven to a temporary storage area and placed on sand bunds.
For the final load-outs, the monopiles were driven back to the quayside and lowered into concrete cradles, ready to be lifted onto the delivery vessel using its on-board crane.
By overcoming the tidal constraints and the limited ground-bearing capacity of the quay, it made it possible for up to ten monopiles to be delivered at a time instead of eight or nine.
Over the duration of this year-long project, several trips from China were spared as a result. With each voyage taking around 60 days of sailing, the time and cost savings were significant.
