NOVELTY - The generating apparatus (10) has a power wheel (34) arranged for rotation about a vertical axis with respect to a hub (32). A shroud is rotationally mounted on the hub and arranged to cover the rotor vanes (36) of the power wheel. A directional controller is adapted to hold the shroud in a predetermined rotational position relative to the hub dependent on the direction of the horizontal water flow. A generator (30) is provided on the hub and adapted to produce electrical power from rotation of the power wheel relative to the hub.    USE - Generating apparatus for converting kinetic energy from horizontal water flow to electrical energy.    ADVANTAGE - The hub includes hydraulic brakes which can lock the power wheel to the hub to prevent rotation during maintenance and lifting or raising. The apparatus can be used in any depth of water, from 10 m to 100 m or more with the use of a suitable support structure is used. The apparatus can operate efficiently over a range of tidal flow rates, by adapting the load on the wheel to the flow rate, through varying the number of operational generators, so that the wheel rotates at an optimum speed whatever the tidal flow rate. Since the wheel rotates at a substantially constant optimum speed, each of the operational generators, when active, operates at a substantially constant optimum speed. The apparatus is efficient since it balances the inertial effect of the moving parts. The apparatus can produce up to between 1 and 3 MW in a 4 knot current using a single generator unit of about 6 m in height. The apparatus is environmentally friendly since the rotor vanes do not travel faster than the tidal current and do not present a danger to marine life. Because no parts of the apparatus move faster than the tide, there are no trailing vortices, so there is minimal disturbance to tidal flow downstream of the apparatus, and the apparatus can be placed relatively closely without compromising the efficiency of either apparatus. The apparatus allows a greater density of power generating capacity per unit area than other generating systems. The lack of trailing vortices suggests hat there is no scour, so the apparatus does not cause environmental damage to the seabed. The apparatus does not need a heavy lift vessel for installation because it floats and can be floated and towed to the installation site. The apparatus can be assembled onshore and can be tested onshore by applying electric power to the generator outputs to drive the drive wheel. It can be floated out as a completely assembly, with the power wheel and hub mounted on the support structure, then when it is at the installation site the apparatus can be sunk and fixed to the seabed. The support structure can include a submersible gravity base which presents only a minimal disturbance to shipping while the hub and power wheel are at least 5 m below the lowest water level in operation so that a support vessel can pass freely over them, leaving only the support structure projecting above the sea surface.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a generating method for electricity from a substantially horizontal water flow in a body of water using a generating apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the tidal stream generator.    Generating apparatus (10)    Generator (30)    Hub (32)    Power wheel (34)    Rotor vanes (36)