Unique ‘bring-to-work’ system selected for Ørsted’s hybrid CTVs

Contracts for the CTVs have been awarded to Northern Offshore Services (N-O-S) and MHO-Co.

Apart from their innovative hybrid propulsion, the trio of CTVs will be the first to be equipped with Z-Bridge’s motion-compensated ‘bring-to-work’ transfer system.

The unique transfer system will enable wind turbine technicians to access transition pieces (TP) on Hornsea Two directly from the CTVs, without having to climb up the tower.

Ørsted lead marine specialist Jan Stilling said, “The new CTVs have large battery capacity that makes it possible to stay offshore overnight in hybrid mode, so they are not burning fuel for up to eight hours while the vessels maintain position without anchoring or mooring to a buoy. The new gangways will provide additional support for the extra access required during construction.”

N-O-S will take delivery of its 39-m vessel Energizer in Q2 2021. MHO-Co is due to deliver two 35-m CTVs mid-2021.

The batteries installed on all three vessels can be recharged using the vessel’s generators or via a recharging buoy system that will be tested during the construction phase of the windfarm.

Both designs have been developed to incorporate fuel-cell technology.

MHO-Co’s vessels have diesel mechanical propulsion and a diesel-electric IPS driveline in both hulls. The diesel-electric drivelines can also be powered from the battery pack.

Z-bridge general manager Bastiaan Spruit said, “The bring-to-work system is a fully motion-compensated offshore access system. It will allow teams of four technicians to transfer in a trolley direct from the CTV to the TP platform.

“Eliminating stepping from the vessel to the boat landing and climbing ladders will improve safety. This will also significantly reduce the required visit time per TP, reducing fuel consumption and improving operational efficiency.”

Scheduled for completion in 2022, Hornsea Two will become the world’s largest offshore windfarm, with capacity to generate 1.4 GW of clean energy.