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MEDAL WINNER

GOLD Tetrahedron ultra-high wind turbine lifting crane

Rotterdam-based Tetrahedron has introduced a revolutionary high-lift crane concept suitable for refitting on existing jack-up vessels built in 2008-2009 to install the nacelles and blades of 3.6MW turbines.

The Tetrahedron 45 model focuses on the emerging 13-15MW class of turbines, with the largest Tetrahedron 65 model enabled for 20MW direct-drive turbines.

The company was awarded DNV GL design verification in the summer of 2020. Crane manufacture and assembly will take place in Rotterdam, the Netherlands.

This innovation has the potential to make a huge contribution to the continued deployment of a large number of the earlier installation vessels, which from a business-case perspective were supposed to remain in active service for 20-25 years.

Vessels have so far been able to adapt to larger turbines by continually optimising their use and upgrading to bigger cranes. However, this cycle may be reaching its technical limits as the upcoming 12-15MW turbines have higher nacelle masses and rotors of 230-plus metres. This requires larger crane hoisting capacity and up to 50 metres extra lifting height.

A main limiting factor for these vessels is that they are fitted as standard with luffing boom cranes, characterised by a boom-base rotation point. Load plus own mass must be hoisted, and deck-bending loads increase with size.

Using the Tetrahedron solution, the crane luffing rotation point shifts from the front of the slew platform (crane rotation axis) to a higher elevation on the leg-encircling crane house behind the jack-up leg.

The benefits of this crucial repositioning, together with an efficient force flow through the tetrahedron shape, makes it possible for traditional vessels to lift turbines with capacity ratings of 12MW-15MW while offering the required 50-metre extra lifting height.