The majority of the existing designs of floating wind structures and mooring systems are based on oil and gas technology. These structures are designed for manned operations and have large deck areas for production or drilling equipment. These features are not required for floating wind systems.
The majority of floating wind structures (64%) are based on a Tri-Floater semi-submersible design operating on a fixed multi-leg mooring system. These structures have to be large to accommodate the weather loadings from all directions. Access at deck level will be require at each of the three floats to enable the mooring pull-in winches to be operated. Access to each float at sea level will also be require to enable personnel to access the structure in all direction of weather.
The Spintral floating structure is also a semi-submersible design. The main feature of the design is that the structure weathervanes around a single mooring point.
The structure comprises of a submerged frame supported by 4 off buoyant floats.
The bow float is connected to the mooring system. The structure is long to ensure that the aft section weathervanes around the bow mooring float. The length of the structure will act to minimise the pitching of the floating assembly in bad weather.
The centre float at the aft supports the weight of the wind turbine. As the structure weathervanes to always head into the weather the wind turbine blades should always be heading into the prevailing wind.
The roll on the structure should be minimal. There are two outrigger floats provided to counteract any roll on the structure if required.
Additional outrigger floats are also designed to accommodate tidal stream turbines. Additional outrigger floats can be added to provide mounting points for 5 off 1 MW tidal stream turbines.
This submerged structure has integrated damping surfaces to minimise the heave movement of the structure.
Personnel access will only be required to the bow mooring float during installation, removal and for routine inspection and maintenance.
The main access for personnel will be at the aft of the centre float. This area will be in the lee of the structure so will be sheltered from the prevailing waves.
Personnel and equipment can be deployed onto the top deck are or through into the covered hanger area.
The Spintral floating structure is novel and has been designed around the requirement for a weathervaning mooring system while providing a stable and accessible platform for the wind turbine.