NOVELTY - The turbine has a rotor (31) with an open center such that the blades are mounted between an inner annular rim member (32) and an outer annular rim member (33). The rim member (32) defines a large open center (35) in the turbine, where the turbine is located within tidal flow. A retaining flange (22) and journals or bearings allow the rotor to shift in either axial direction in response to water flow. Rotor is rotated in one of rotation directions relative to a housing (21) and retaining flange, to generate electricity.    USE - Used for producing electricity from low head bi-directional or reversing water flow.    ADVANTAGE - The turbine is located within the tidal flow, and the bi-directional tidal flow operates the turbine, thus producing electricity with water flow in either direction, without having to reverse the orientation of the turbine. The inner rim defines the large open center that increases effectiveness of the hydroelectric turbine in low head conditions, thus enabling construction of the housing and rotor with larger diameter than that of shaft mounted rotors, and hence allowing increase in total surface area of the blade members. The retaining flanges and journals or bearings allow the rotor to shift in either axial direction in response to the water flow, thus reducing the amount of energy required to initiate rotation. The journals or bearings in the axial direction are of increased thickness, thus reducing overall wear on the journals and bearings.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method of reducing the amount of energy required to initiate rotation of a rotor in a turbine    (2) a method of extending the period between required servicing of a turbine for replacement of bearings.    DESCRIPTION OF DRAWING(S) - The drawing shows a view of a hydroelectric turbine.    Housing (21)    Flange (22)    Rotor (31)    Inner annular rim member (32)    Outer annular rim member (33)    Blade members (34)    Open area (35)