Engineering
During the feasibility study, it became clear that the dragging loads during transit required the monopiles to be positioned 3 meters above deck level. This was required due to two aspects: the weight of the monopiles (between 500 and 670 tonnes), in combination with the maximum significant wave height of 2 meters (design criteria). The grillages were adjusted to these parameters. An unforeseen benefit is that the crew can walk freely underneath the monopiles.
As indicated during the proposal period, Conbit recommended using friction to hold the monopiles in their grillages. Each monopile would be kept in position using grillages with two saddles on top. Initially, the friction was obtained by a sort of lashings. Four of these lashings were used to pull down one saddle, which lay on top of the monopile. By connecting two lashings on each side of the monopile and pulling them together, it should be possible to manually get the required load of 100 metric tonnes in each lashing. This system later proved unable to fulfil the requirements and a different system was implemented. The improved system involved the same lashings, but a hydraulic tensioning system would generate the load.
An unique benefit of the seafastening system is that it enables the load to be monitored throughout the entire transit period. The system is fitted with load cells, which measure the force in each lashing. The load cells transmit the data to a computer system. The captain of the Zaratan can then view the load values from within the control tower. If he observes any abnormalities in the load cells, he can adjust his route or assign a crew member to increase the load.
Since the saddles, like everything else on the Zaratan, are big objects, they need to be stored during transit back to shore. Conbit was asked to provide a kind of saddle rack. This rack is positioned on deck close to the grillages, so the saddles can be placed on them using the onboard auxiliary crane.
The other part of the contract covered the transport of the monopiles over the main deck. The main deck crane can lift 1,000 metric tonnes, but has a reach limitation; the monopiles need to be moved in both longitudinal and transverse directions to enter the crane's reach. In the past, several methods have been used to perform these actions. Conbit proposed a method using SPMTs. These multi-wheel trailers are uncommon in an offshore environment; nevertheless, Conbit was able to convince the client of the benefits.
After the preliminary design was finalised, it became clear that the SPMT would be unable to lift the monopiles high enough. The Conbit engineers came up with a suitable solution: cradles were designed to gain the extra lift height. The cradles are operated with a remote control and are powered by the SPMT power packs. When the cradle is in its highest position, it can lock the system before the multi-wheel trailers start to move. With this innovation, Conbit showed that with some adjustments, onshore equipment can be made suitable for offshore applications.
Procurement
In projects like this, it is often cost and time efficient to let the engineers handle procurement as well. Quotations can be requested in early engineering stages and engineered solutions can be modified throughout the process to improve the cost-quality ratio. This approach has a lot of advantages compared to the traditional approach, which required the engineer to be finished designing before the procurement process could begin.
Seajacks awarded Conbit with a procurement contract for the equipment designed by its engineers. The procurement process was started early in the project. Qualified suppliers were selected. A total of 18 subcontractors were contracted.
The Conbit team coordinated the procurement process and managed to transport the items in time to the desired location.
The Germanischer Lloyd guidelines applied to this project, meaning that all items had to be traceable and the quality guaranteed. Conbit was in charge of coordinating certification. In practice, this means that fabrication of steel parts must be witnessed by a third party. All material certificates must be available, as well as the welding qualifications of each welder. Other components need to be (load) tested. Log books of all these tests are part of the completion documentation and without them the project cannot be completed.
Construction
After successfully passing all factory tests to the client's satisfaction, the equipment and materials were transported to Amsterdam. At the Shipdocks yard in Amsterdam, the Zaratan jack-up vessel was commissioned. Conbit’s equipment and all other equipment were installed onboard in a very short period, and final tests of the equipment were carried out onboard. On the morning of Monday, 27 August, the Zaratan left to Cuxhaven, where it would start its first big job. Seajacks was awarded a contract to install 78 foundation piles for the Meerwind offshore wind park. The Meerwind Offshore Wind Project consists of 80 Siemens wind turbines with a power output of 3.6MW each.
The Conbit team would like to thank Seajacks for the opportunity to be part of this wonderful project team. We wish the Zaratan and its crew a safe and prosperous voyage.
