A hydrokinetic turbine is adapted to slow water energy conversion to avoid adverse environmental impact on tidal flushing. It combines a large bulbous upstream hub with a peripheral array of current deflectors downstream of the hub. The deflectors are analogous to delta plane wings at high angle of attack, but here are oriented to cause both tangential and radially inwards angular acceleration of ambient flow. Torque develops in reaction to these angular accelerations, in contrast to Bernoulli effect lift on high aspect ratio foil sections that require high surface flow speeds. The fluid accelerations further combine to form a vortex in the turbine's turbulent wake, which draws additional water through the deflector array. In one embodiment, the deflectors' support members pivot about their inner ends in the mode of a rotary kite that may economically project a resilient structure over a very large area. In another embodiment, the entire turbine may submerge to permit passage of deep draft commercial shipping traffic.