Abstract: A tidal stream or ocean current turbine is connected to a submerged buoy that is tethered to the seabed to create a virtual seabed level that is higher than the actual seabed. The buoy is constrained by tensioned tethers or catenary mooring lines such that it is approximately geofixed at a prescribed depth of immersion and orientation. The turbine device is attached to the submerged buoy by a connector strut that allows the device to swivel about the geofixed location. The strut to buoy connection incorporates a bearing system that allows the strut freedom of rotation in the horizontal and vertical planes about the geofixed buoy. The reserve of buoyancy in the submerged buoy acts to resist the vertical component of the mooring force such that the drag force on the turbine device cannot lead the device to submerge excessively or cause the downstream tension tether mooring lines to go slack.

Abstract: A floating, semi-submerged, tethered device that supports a horizontal axis turbine and power generation equipment for extracting kinetic energy from a tidal stream or ocean current. A submerged body (1) is supported by surface piercing struts (2) of small water plane area (FIG. 6). The device is tethered to the seabed by a spread of mooring lines (12) that are deployed both into and away from the direction of the tidal current. A horizontal axis turbine (4) harnesses energy from the water flow and drives a generator housed within the body. A horizontal strut hydrofoil (24) corrects the trim of the device when subject to varying loads from the mooring system and can also be used to dampen pitch motion. Rudder flaps in the struts (25) can be used to counteract roll motion. Power is exported from the device to the seabed by an umbilical (17).