ENERGY Ӏ OFFSHORE WIND POWER
space for ever-larger facilities and equipment. In these cases ingenuity has been key – as, for example, Mammoet’s solution for offloading transition pieces at the port of Nigg for the Moray West offshore farm (see box opposite.) Indeed, ingenuity has led to a whole new category of crane being created for handling offshore wind turbine items; in July Dutch company Tetrahedron completed a 130m prototype. The design has a completely new motion principle and structural force flow compared to conventional cranes, the company says. A large scale non-slewing
prototype shows this new motion principle; and the different force flow was verified based on strain and deflection measurements. The design claims the advantage of higher lift compared to a luffing boom crane. The prototype was assembled according to plan and the crane performance meets the design requirements and matches the predictions of the design and engineering phase, say Tetrahedrons designers. The Tetrahedron prototype
crane’s drive and control systems are fully electric. A fast and smooth luffing motion reaches 130m lifting height above ground level – it would be only 90m for a luffing boom crane with the same footprint. A very slender jib creates
freedom to move the load, which is of interest for blade handling operations; and real time sideload measurement, which again is of special interest when lifting loads (i.e blades) that are designed to catch the wind. The prototype has been erected
onshore but was intended to demonstrate the Tetrahedron crane’s offshore suitability for wind turbine handling, especially when installed on compact jackup vessels with tubular legs, where it would
34 CRANES TODAY
The Tetrahedron
crane – a new concept
be capable of maintenance work on 10MW wind turbines. These compact jackup vessels
are nowadays typically used for accommodation and light works. At the start of the project there was little demand for such compact accomodation jackups and they would have been readily available for mounting such cranes; but, as we have seen, demand now is too great for the option of modifying these vessels towards wind turbine maintenance units. Therefore the installation of the Tetrahedron prototype crane on these vessels is for the moment suspended,
and the prototype crane remains onshore for demonstration purposes waiting for a later-to-be- defined destination. But offshore wind generation is not going away. Of all the non- fossil-fuel resources it remains the most practical, the most present, and the fastest-growing. Whether tower can get taller still and blades still longer is for engineers to determine. The lifting industry will find responses to the challenges that are set. Those responses will require imagination, ingenuity and hard work. Read these pages to follow them.
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