The Wagenborg Stevedoring yard in Eemshaven, Netherlands is a busy spot these days, being the logistical centre for a number of offshore wind parks. The preassembly of wind turbine components is also carried out at the site. This means jack up installation barges can take preassembled parts offshore, minimising construction time at sea.
The Alpha Ventus offshore wind park consists of two sets of six 5 MW capacity wind turbines. Wagenborg Nedlift assisted with the preassembly and loading of the wind turbine parts at the Wagenborg Eemshaven yard.
Once the 750 tonne foundations, the 150 tonne main piles and the generator set, weighing 325 tonnes, were in place, it remained for the rotor star, consisting of an 85.5 tonne rotor and three blades, weighing 16.5 tonnes, to be installed in one piece.
Firstly, the blades and rotors were put together with cranes and rigging personnel from Wagenborg Nedlift. The complete rotor star weighed 135 tonnes and had a diameter of 120 m. Now the preassembly was complete, the jack-up barge could pick up the whole piece and carry out the installation offshore.
The customer's initial plan was to jack up the barge to 50 m, so the jack-up piles would not interfere with the blades during the lifting operation. On the drawing table, this seemed a feasible plan. However, in reality, this was a risky operation because of the wind levels offshore against the huge rotor star.
Therefore, the plan was called off and the jack-up barge stayed on quay level. To properly position the rotor star on the quay, the jack-up barge had to make a turn of 180 degrees in order to make space for the blade that pointed towards the water. Turning the jack-up barge caused another problem: the required radius was too large for the barge-mounted crane to lift the complete rotor star.
At that point, on a Saturday afternoon, the Wagenborg Nedlift project engineers received a call from their colleagues at Eemshaven, who were managing the job there. The question was how to get the rotor star within reach of the jack up barge crane, now the barge had made a turn? In the initial plan, the rotor would be transported by SPMT to quayside, leaving 3 m of space. In this new situation, radius was 6 m greater and the barge crane could only pick up its load when it crossed the quayside. Getting the jack-up barge closer to the quay was not an option due to possible damage to the quay. It seemed an unsolvable issue.
But Wagenborg Nedlift personnel persevered and after a few hours of engineering, calculating, checking, re-checking and discussion, a solution was found. In principle, the SPMT trailers would be used as a balance. On one side, 180 tonnes of counterweight was positioned. On the other trailer side, the rotor star was positioned. At quayside, the barge crane took part of the load, while SPMTs drove further, leaving 2 x 2 axle lines above the water. As the SPMTs drove further, the barge crane's capacity increased and after 3 m, the barge crane could take over the full weight, 135 tonnes, of the rotor star. The SPMT trailer was moved slowly back on land again.
With this creative solution, Wagenborg Nedlift's project managers and engineers prevented a major delay in the project. The offshore installation contractor and principal of the project were very satisfied with the final result, said the company. n