Abstract: A hydroelectric turbine for the production of electricity from tidal flow forces, the turbine having a rotor preferably with an open center such that the blades are mounted between an inner rim and outer rim, wherein retaining members and anti-friction members are provided to limit movement of the rotor relative to the housing in either axial direction, such that water flow in either direction operates the turbine, but wherein the retaining members and the anti-friction members allow the rotor to shift in either axial direction in response to water flow, thereby reducing the amount of energy required to initiate rotation. The anti-friction members limiting rotor travel in the axial direction are preferably of increased thickness, such that as the anti-friction members wear down, the rotor is able to shift relative to the housing in the axial direction.