On behalf of Lloyd-Werft Bremerhaven AG, the Sarens Group recently lifted two sets of four gigantic jackup legs onto two offshore installation vessels belonging to RWE OLG GmbH, a logistics company that is part of RWE Innogy, at the free port of Bremerhaven. These legs enable installation vessels to lift themselves up from the water in the middle of the sea while installing wind turbines. The Sarens team relied on two Terex CC 6800 Crawler Cranes to lift the 630-tonne, 78 meter-long steel colossi with the assistance of a floating crane.
RWE subsidiary Innogy commissioned a South Korean shipyard to build two installation vessels designed for erecting offshore wind farms: the “Victoria Mathias” and its identical sister, the “Friedrich Ernestine”. Both self-elevating vessels arrived at Bremerhaven in February 2012, but without their jackup legs, which were left behind in South Korea due to the fact that it would be easier to ship them separately. A couple of months later, the Sarens Group and its specialists were specifically chosen for the challenging task of installing the legs, which were just under 80 meters long and had a diameter of 3.75 meters.
Installation and lifting under adverse conditions
In order to lift the 630-tonne legs, the Sarens Group decided to use two Terex CC 6800 Crawler Cranes. “Given that the loads’ enormous weight required the use of two cranes, it was definitely a good idea to use two units of the same exact model so that we could ensure that everything would be perfectly synchronized,” reports Jelle Schepens, a project manager at Sarens. Before the lifts could start, however, it was first necessary to reinforce the port wharf so that it would be able to bear the weight of the two cranes together with their loads. To do so, a concrete slab with a thickness of 1.40 meters and an area of 30 by 35 meters was sunk into the floor in front of the dock, and was used by the Sarens team to set up both CC 6800 units. While one of the two cranes was brought to the site “conventionally,” i.e., by land, the other was brought by ship from the US to Bremerhaven – all the way to the wharf wall so that it could be set up on the slab directly from the ship. However, some of the crane’s parts also had to be delivered by land. A total of around 80 trucks were needed in order to transport all of the required components for the two CC 6800 units to the site, and a total of two weeks were required by the eight-person Sarens team in order to set them up. The team not only had to deal with the constrained space conditions at the site that resulted from sharing the wharfage with the vessel outfitters and their building materials, but were also faced with a unique situation: Since the assembly was being performed at a free port, the project was legally considered to be taking place abroad in non-European territory. In other words, all building materials and components had to go through customs in order to reach the site, which not only entailed an enormous amount of administrative work, but also made the scant time available for the project all the more dear: After all, the “Victoria Mathias” was scheduled to be christened on May 21st, and the job had to be completed by then without fail. To make matters even more complicated, the weather decided to take a turn for the worse as well: “We had to wait four days until the wind slowed down to less than 10 meters per second, and the conditions weren’t right for the job until May 17th – four days before the christening,” reports Schepens.
Smart “leg work”
As a result, everything had to be done at record speeds and further delays had to be avoided at all costs. The Sarens team set up the two CC 6800 units with the same exact SSL-LSL configuration and a 108 meter-long boom, as well as a counterweight of 250 tonnes on the superstructure, 80 tonnes of central ballast, and a 240-tonne superlift counterweight on the 24 meter-long superlift boom. This put the two cranes in an ideal position to lift the jackup legs, which were waiting on a pontoon. In order to make it possible to perform the lifts evenly with the required lifting capacity, the hooks on both cranes were connected to a heavy-load spreader. “We placed angular position sensors on the spreader so that both crane operators would immediately be alerted if it became tilted and would be able to balance it out right away,” explains Schepens. After all, the lift operations required not only speed, but also laser precision. In order to perform the lifts, the two CC 6800 units picked up the legs from their head end and hoisted them with the help of a crane vessel, which followed their lead as it moved the opposite end in a controlled manner while the legs were being vertically raised. Once the jackup legs had been placed in a stable upright position, the floating crane was disconnected and removed, after which the legs were lifted to a height of 95 meters by the two Terex cranes and swung within a working radius of 21 meters above and beyond the vessel’s deckhouse until they reached the required position. A tugboat then towed the installation vessel to its exact required position so that the legs could be lowered down into position in the vessel and bolted there. “Of course, the fact that the jackup legs were so heavy meant that there was always the risk that the ‘Victoria Mathias’ could list and capsize due to the one-sided load,” explains Schepens. In order to prevent this, the ship was balanced with water with perfect synchronicity on the opposite side while the legs were being lowered into place, which of course took additional time.
Despite all this, the Sarens team was able to perform each lift smoothly and on schedule so that the ship’s christening was celebrated as planned on May 21st. The lifts for the second installation vessel, the “Friedrich Ernestine”, at the beginning of June were a comparatively relaxed affair for the Sarens team. “We knew at that point that all our calculations and plans were correct and that there was no reason to expect any undue difficulties – if anything, this shows that even an extraordinary job like this can almost be turned into a routine assignment with the right machinery and a good team,” summarizes Schepens, completely satisfied with his team’s performance.
About the Terex® CC 6800
Offering excellent lifting capacities across all working ranges, the Terex CC6800 lattice boom crawler crane provides a nominal lifting capacity of 1250 tonnes for a maximum load moment of 13.840 meters and 216-meter maximum tip height. The superlift radius can be adjusted from 15 to 24 meters. Highly simplified assembly processes ensure short rigging times to start working rapidly for excellent return on investment. Capable of travelling speeds of up to 1.1km/h, the CC6800 is equipped with a powerful Quadro-drive and hydraulically-assisted boom section pinning system as standard.
About the Sarens Group
The Sarens Group, which is headquartered in the Belgian town of Wolvertem, employs around 3,000 people and is one of the world’s leading providers of crane and heavy-load transportation services. Its customers include companies from the petroleum and gas production industries, the energy industry, the petrochemical industry, and the mining industry. In addition, the company has a separate business unit that specializes in the erection of onshore and offshore wind turbines. Sarens enjoys an outstanding reputation as an unrivaled business partner in every single one of these industries, and all the more so when large-scale, complex lifting projects are involved. The family-run enterprise, which was founded in the 1930s, now boasts 101 branch offices in 51 countries.
For more information, please visit www.sarens.com
Terex Corporation is a diversified global manufacturer of a broad range of equipment that is focused on delivering reliable, customer-driven solutions for many applications, including the construction, infrastructure, quarrying, mining, shipping, transportation, refining, energy, utility and manufacturing industries. Terex reports in five business segments: Aerial Work Platforms; Construction; Cranes; Material Handling & Port Solutions; and Materials Processing. Terex offers financial products and services to assist in the acquisition of equipment through Terex Financial Services. More information can be found at www.terex.com
Author; Agustin Dominguez