11,700 mt Jackup platform for Africa
Recently, BigLift Barentsz loaded an 11,700 mt jack-up platform in Vlissingen, the Netherlands, to transport it to West Africa.
The jack-up platform has an overall breadth of 75 m and its legs are 133 m high. With a large, flush deck of 125 m x 42 m, high deck strength and a uniform grid of bulkheads and web frames, combined with a sophisticated ballast system, BigLift Barentsz was the right vessel for the project.
With the assistance of an advanced weather and acceleration monitoring system onboard the vessel, the platform was safely delivered within three weeks.
Entire Engineering Scope
Once the contract for the transportation had been signed, the detailed engineering started. In the enquiry phase, a feasibility study had been made, which mainly concerned stability calculations and the assessment of operational challenges. However, the weight of the jack-up platform was not an issue for the ample deck strength and hull bending capacities of the BigLift MC Class.
After calculating the sailing conditions of the vessel, accelerations during transportation were determined. Using an in-house tool and data from various sources, accelerations and predictions could be made that formed the input for calculations for the required seafastening and deck loads.
One of the main challenges for this project was that there was only limited information about the platform. It is over 30 years old and valid drawings and strength calculations were unavailable. Therefore, the structural integrity of the platform was assessed several times prior to the loading operation. Within this contract, BigLift was responsible for the entire engineering scope, so it calculated and designed the seafastening, as well as the structural capacity of the platform in-house.
Precise and Accurate Positioning
The distance between the legs of the platform is 47 m and as the vessel has a beam of 42 m, bringing the vessel in between the legs was a meticulous process, which required thorough planning and careful execution.
The platform stands on spud cans, which are wider than the legs and increase the standing area on the seabed, but the extra width decreased the space between the legs and the flank of the vessel to only half a metre on both sides. Precise and accurate positioning was therefore key.
For this manoeuvre, cross-wires, bow anchors and a stern tug were used. Once the vessel was in position, the platform was lowered onto the deck of BigLift Barentsz, until the platform touched the deck and the vessel’s draught had increased by 10cm. Then BigLift Barentsz started its de-ballasting procedure. Due to the vessel’s large ballasting pumps it took only about two hours to take over the entire weight of the platform. It was now resting almost completely on the vessel.
At that point, the legs were pulled up one by one and after all three legs had been raised, the vessel sailed into her berthing position. As the platform was wider than the vessel, spacer barges were used to provide 15 m extra space between vessel and quayside in order for the platform not to touch the quay.
As the bottom of the platform was not completely flush, a detailed drawing of all the protruding items had been made to design the optimum cribbing grid. After selecting the right type of wood – not too soft, not too hard – a tailor-made grid was designed and laid out to keep the cribbing pressures within all limits.
In winter the sea in North-West Europe can lead to some serious accelerations, which can shift cargo away from its original stowage position.
To avoid any movement, a custom-made seafastening system was designed that ensured enough redundancy but also made it safe and easy to install.
Despite a very short lead-time – only three weeks between signing the contract and starting loading operations – all the design and engineering, procurement and construction was completed on time by BigLift’s in-house project team.
And only another three weeks later, the jack-up was delivered safely to its new working position.This shows the relevance of hiring a specialised company, with skilled people and a technically advanced vessel.