Forewind pioneers new technique

Offshore wind consortium Forewind has pioneered a “human-free” installation technique to mate a meteorological mast tower to a fixed foundation at its vast Dogger Bank project.

The method, dreamt up by Norwegian outfit Fred Olsen, which also supplied the innovative “suction bucket” foundation structure, uses heavy-duty plastic cones strapped to the tower to guide the met mast into place as it is installed by crane.

With the new technique, the construction crew do not need to manually position the met mast lattice tower, removing the risk of handling a swinging or falling load.

Fred Olsen health, safety, environment and qualitymanager Jan Fredrik Platou says it was “safer than traditional methods, but also much faster, as the cones helped to quickly stabilise the load in the final stage of the lifting”.

Forewind general manager Lee Clarke describes the innovative installation technique as “another example of the potential safety and efficiency gains to be made through developers and contractors working closely together”.

Installation of the 44-tonne galvanised steel tower for the Dogger Bank met mast - one of a pair deployed by Fred Olsen Windcarrier’s jack-up vessel Brave Tern - was handled by contractor SeaRoc.

The flask-shaped 165-tonne steel suction bucket foundations, built at Belfast’s Harland and Wolff yard in Northern Ireland using a design from Fred Olsen acquisition Universal Foundation, are being trialled as a cost-cutting option for turbines in mid-range water depths.

The bucket foundation concept is based around a squat cylindrical “skirt” that pulls itself down into the seabed using a system of high-pressure pumps so that the soil becomes a structural support to root the tower and turbine in place. It was developed through the UK Carbon Trust's technology-mentoring Offshore Wind Accelerator scheme.

Installation of the foundations marks the first stage of construction at the 9.6GW, £3bn ($4.53bn) Dogger Bank zone, 125km off eastern England's coast, where water depths range from 18-63 metres.