Rocksteady tensioning tool will save millions for floating wind

The Rocksteady tensioning tool (TT) is a novel subsea mooring line tensioning system designed to simplify the installation and replacement of mooring lines on floating offshore assets. 

The patented method supports efficient offshore operations and levelised cost of energy, by using a single tensioning system for the entire field. Its benefits include 

• Much lower capital cost
• Comparable or lower OpEx (operational expenditure)
• Lower risk
• Simple & accurate line tensioning

Using a single pull-in and winching operation for connection, the TT zips up mooring lines to final tension using a removable and reusable winch, saving millions in CapEx (capital expenditure) for floating offshore wind.  

Much lower capital cost 

The key benefit of TT is that it does not require any external tensioning interface and no tensioning equipment is left in the system. This means: 

• A single rental Rocksteady TT is required to tension an entire field of floating wind turbines.
• The two halves of Rocksteady TT are drawn together by a surface winch to make a quick connection under final tension, quickly, easily, and repeatably.
• No chain stoppers or tensioning systems are needed to be maintained on the offshore asset. The mooring lines attach to padeyes. Expensive and heavy fairlead systems are not required. 

The rental of the Rocksteady TT is included as part of the installation service and the only component left behind is a type-approved Rocksteady subsea mooring connector. 

Comparable or lower OpEx  

No platform adjacent operations are needed, avoiding personnel transfer and seabed operations with poor visibility, as well as avoiding cutting chain subsea and its inherent risks. 

Lower risk 

Using a single connector away from the platform reduces the splash zone, as well as bending and high-tension locations, and lessens biofouling and mudline fouling.

Simple & accurate line tensioning 

Rocksteady TT is an efficient choice for both catenary and taut leg polyester mooring lines, as no chain is needed for the tensioning process. Polyester lines that require creep control can be fitted with a short length of chain or rope that is simply removed or shortened following the same tensioning process.

The required tension is calculated from an accurate survey, catenary calculations and advanced system analysis. This analysis is used to directly set the installed line lengths, rather than measuring tension. The tension is verified by the surface vessel winch and optional load cells subsea or on the offshore asset hull. This simplifies the installation process, enabling crews to accurately set final mooring line tensions irrespective of the hookup procedure.

The Rocksteady TT is one way Acteon encourages innovation to optimise anchor and mooring system designs for floating wind. It has been selected by InnovateUK iX, a UK programme aimed at speeding up knowledge transfer and driving innovation.