Efficiency of a horizontal axis wind/water turbine (HAWT) is increased by the addition of a secondary blade associated with each main blade. The secondary blade is preferably a blade segment paralleling the main blade only in the outer reach of the main blade. The secondary blade travels rotationally ahead of the main blade and axially behind it, in an area in which air has not been disturbed by the main blades and in which disturbance of air by the secondary blade is not seen by the main blades. In one embodiment the secondary blade is carried by its associated main blade. In another embodiment, the secondary blades are carried by a ring or wheel which rotates with the main blades and the axle to which they are attached.