Pliosaur Energy - technology
A novel taut mooring system is used to anchor the turbine to deadweight anchors located fore and aft on the sea bed. The use of a semi-submersible structure, a vented turbine cover and a 3rd party procured anchor cable shock absorber (Supflex) ensures that the wave impact forces are within design parameters.
The anchoring system on the turbine consists of a cylindrical member(mooring post) with a submerged anchor chain pulley mid length which connects the upper and lower parts of the turbine. This mooring post is fully retractable and as several are utilised to moor the turbine, this can be accomplished onsite thereby facilitating the IMO 5 yearly anchor inspection requirement without need for dry-dock. Following disconnection from the mooring post the anchor chain assembly can be fully recovered without the need for divers.
Each deadweight anchor is constructed from reinforced concrete and floated into position in a similar way to bridge caissons. Once in position, it is sunk in controlled manner by partially flooding the deadweight anchor. After confirmation that the anchor is correctly located it is fully flooded with sea water to complete the ballasting process. Decommissioning is the reverse where air is pumped inside the deadweight anchor to remove the sea water and thereby refloat it to surface before towing to a safe disposal location for disposal. This approach sets new environemntal standards by minimising the environmental impact to the local benthic (seabed) community during the installation and decommissioning process.
The anchor chains are fed through the deadweight anchor body via holes fore and aft. The anchor is a cylindrical plate fastened to the end of the anchor chain with a diameter larger than the deadweight anchor holes. Recovery of the anchor chain, once the shock absorber is disconnected, is achieved by connecting a recovery line to an eyelet on the anchor plate and pulling the anchor chain back through the deadweight anchor body.
The mooring system has been specifically designed to have a very low anchor cable angle thereby minimising the anchor cable tension induced uplift forces at the deadweight anchor and the additional buoyancy requirement at the turbine.