Abstract: A runner for an hydrodynamic machine comprises fixed runner vanes mounted in a predominantly radially oriented part of an annular channel defined between a crown and a skirt ring, and a crown tip attached to the crown and defining with the skirt ring a predominantly axial portion of the channel. Fins attached to the crown tip deflect the flow leaving the runner vanes to eliminate essentially all vortex flow when the turbine operates above an optimum condition. The fins are substantially triangular in shape and are located with the apex portion nearest the runner vanes and the base portion remotest from the vanes. They are curved along their length, the apex being substantially aligned with the flow from the vanes and the base being aligned to deflect the flow in a direction generally with the axis of rotation of the runner.