Words: Wouter Slob, Tender & Concepts Engineer, Huisman, the Netherlands
The development of current and future offshore wind farms is picking up with wind installation contractors further optimising their toolboxes for efficient installation of offshore wind turbines. Up to now the jack-up vessel has been the platform of choice for installation of wind turbines; providing a stable platform, which when jacked up, uses a crane which reaches high enough to install the nacelle of the wind turbines.
Building larger size jack-ups is a costly affair; the Foldable Offshore Crane offers a crane solution, which can increase the installation capabilities of such an asset, offering the same effective lift height with a shorter crane, compared to conventional fixed boom cranes while increasing the payload capacity.
With the ever increasing size of wind turbines and the need to make efficient use of the stable platform provided by jack-up vessels, it is invaluable to be able to increase the lifting envelope of the crane, both in height, width and load.
This can result in a vessel layout on which a crane boom extends far beyond the main vessel dimensions. In this setup the boom is largely unsupported during transit conditions, resulting in unwanted fatigue wear. The large overhang also makes it more difficult to manoeuver the vessel in port or restricted areas and results in the need for a larger mooring length, increasing docking costs in port.
The unwanted fatigue wear can be resolved by adding more steel to the boom. The added steel will result in a weight increase, negatively affecting the crane’s capacity and also decreases the vessel payload; all unwanted effects resulting in a weight increase, which are only needed for ensuring the crane’s integrity in transit mode.
With these design constraints and effects in mind a new crane concept was born: the Foldable Offshore Crane, or FOC. It features a long boom, to which a foldable boom is attached.
