Start-up Tetrahedron has designed a crane that can lift wind turbine components up to 50 meters higher than conventional cranes. Thanks to a completely different motion mechanism and efficient force distribution, existing jack-up vessels maintain deployable to install wind turbines above 10 MW. An interview with founder Wilco Stavenuiter.

For which problem have you found a solution?

“Offshore cranes have been developed for oil and gas platforms. These cranes have a lifting height of about 100 meters ánd a reach of 100 meters. Offshore wind turbines are tall but slender and so require more lifting height and less reach. Wind turbines are getting higher and higher. The next generation of 12-14 MW turbines will require lifting heights of 180 meters above sea level. The existing fleet of jack-up vessels that install towers, blades and nacelles with conventional (luffing) cranes is no longer deployable. Those ships can lift a maximum of 150 meters. This cannot be solved technically. That is why half of the jack-ups are now anchored or carry out small jobs. For 10+ MW turbines jack-up vessels are being built that are 1.5-2 times as large with twice as large cranes, an investment of 300 million USD. With our design we keep existing jack-up vessels relevant.”

What is the core of your solution?

“We have designed a crane especially for offshore wind turbines. Our crane has the shape of a tetrahedron, a 3D-triangle. The arm of the crane is held up by two cables, the pendants. These fixed-length cables transfer arm and component force flows very efficiently, including lateral forces. At the bottom, the pendants are attached to the crane arm via a V-shaped steel construction. The tetrahedron structure is luffing up and down around the aft hinge. The slewing mechanism to rotate the crane around it’s z-axis is just like a regular crane based upon a slew bearing. The 3D-shape of the Tetrahedron makes the crane very suitable to be positioned around the leg of a jack-up. In addition we have developed a software program, the Automatic Crane Engineer (ACE), that can automatically calculate the static and dynamic loads for lifting various wind turbine components.”

What is so ground breaking about your crane design?

“The revolutionary thing is the combination of the force flow distribution and the movement mechanism. Revolutionary is that the crane's pivot point is not at the bottom of the front, but at the top of the back. And the use of the tetrahedron-structure. As a result, the crane can lift up to 50 meters higher without other disadvantages. Apart from that, we make use of existing techniques and materials. Hence our motto: ‘simply lifting higher’. The ACE software is also ground breaking. Instead of having an engineer calculate for days, the program provides the results of a complete design optimization within a few minutes.”

What are the benefits of your crane design?

“Most importantly, this crane can be mounted on existing jack-up vessels. By upgrading these vessels they can lift up to 50 meters higher. This makes them suitable for the 10+ MW generation of wind turbines. As a consequence, the current jack-up fleet does not have to be downgraded to lower tier jobs. They can last for years for half of the price of a new jack-up vessel. This not only saves major costs in this ‘’hot’ market, it is also better for the environment."

What are your challenges?

“It is extremely complicated to calculate the geometry of such a completely new crane. We put a lot of effort into that, but we have solved it. Our biggest challenge now is to convince manufacturers and contractors that our crane actually works, to demonstrate how simple it is in the end. They are so familiar with a movement mechanism at the front that it is difficult for them to lean on to a completely different principle. It's easy to get them excited with a pitch, but to really convince them that it will work better and that it can be built, we need a demonstration model."

Where are you now?

“The basic design is ready. We have applied for a patent. Working out the details is a piece of cake for us. At DNV GL, we have successfully completed the 'Design Verification' step. This means that the crane can be built and certified according to their crane codes. This independent verification is essential to be able to conquer a position in this market.”

What are your next steps?

“We launched our crane design very recently. We are now intensifying our contacts with partners and subcontractors. We prefer to do business with regional partners. With DNV we will compile a test plan for each component; you cannot perform a full test in one go. We are also looking for a launching customer who wants to use the first crane on an existing jack-up vessel. If a customer says: ‘Can I have such a crane?’, we can deliver it in 2022 in Rotterdam."

What are the benefits of TKI Wind op Zee and Offshore Wind Innovators?

“We benefit from the professional network of Offshore Wind Innovators and TKI Wind op Zee. We enthusiastically participate in these networks. In addition, we have received a R&D subsidy from the Top Sector Energy. Together with Van Oord, DNV GL and Delft University of Technology, we can take major steps in knowledge development and a professional cooperation structure.”

Product information: www.tetrahedron.tech

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