A turbine wheel on a horizontal axis is coaxially mounted within a primary nozzle, for support in a fluid current below a platform carrying electrical power generation equipment. The turbine wheel and primary nozzle are submerged and oriented to enable flow of a portion of fluid current through the nozzle and past the turbine wheel.The turbine wheel comprises a shroud-ring rim, a set of blades extending inwardly toward the axis, the blades being mounted at their outer ends on the inside of the rim, and at their inner ends on the outside of an axial hub. Each blade has its longitudinal tensile elements shaped in the form of part of a relaxed catenary, extending from rim to hub, with sufficient bow in the direction of force of fluid current on the blade to provide a practical wheel of reasonable cost. Struts and strut vanes supporting hub elements within the nozzle may also be of relaxed catenary configuration.