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).