New monopile installation system

The technology should offer substantial savings on installation work in the offshore wind farm sector. Developed jointly by MacGregor and Kongsberg Maritime, this new gripper system is claimed to extend the weather window when installation work can operate.

Offshore wind farm installation operations face challenges from the increasing size, weight and height of turbines. This has led to demand for a new generation of installation and maintenance vessels designed to cope with these increasing challenges. Jack-up vessels are mainly used, equipped with pile-grippers on static frames, combined with complex mooring arrangements to hold the pile steady until it can be secured.

“A pile standing on the seabed will self-penetrate to a certain level, but it is not stable,” explains Kristina Arutjunova, Director of Sales and Marketing Innovations at MacGregor. “Wave forces can be considerable, therefore the pile must be held still by a guiding frame on the vessel until it is driven down to a stable position. If the vessel is moored very securely, and the sea state is calm, a traditional pile-gripper, fixed to a static frame, can be used.”

With a view to extending the weather window for operations MacGregor and Kongsberg Maritime embarked on a joint development project using automated solutions. Its aim was to deliver significant improvements in the operability, productivity and efficiency of future generations of monopile installation vessel fleets. By applying motion-compensation technology, coupled with dynamic positioning to the monopile installation process substantial savings could be achieved and the new pile gripper system is the result.

“Our newly-developed pile installation method represents a considerable improvement over traditional methods,” Arutjunova commented. “Essentially, the motion-compensated pile-guidance frame ensures shorter installation times and increases operational weather windows, adding up to substantial cost savings.”

The new pile-gripper solution comprises a motion-compensated, hydraulically-operated pile-gripper that is controlled by a guidance control system which works in tandem with the high-precision DP system and provides a coordination link between the pile-gripper and the DP system from which a servo control system translates vessel motion and monopile position data to movement in the actuating cylinders and also monitors loads and the status of the pile for feedback into the guidance system.

By Jake Frith