A unidirectional hydrokinetic turbine having a water entrance end and a water exit end defining a single direction of water flow through the turbine, comprising: a generally cylindrical accelerator shroud that has a length extending from the water inlet end to the water exit end and comprises a radially inner wall surface and a radially outer wall surface spaced apart from the radially inner wall surface, to form a radial wall cross-section, wherein the radially inner wall surface defines within its cylindrical cross-section a water flow area; located within the water flow area an integral hydrokinetic force-generating member, that rotates as one unit in a single direction in response to water flow in said single direction during force generation within the accelerator shroud, the integral force-generating member comprising: a center hub member having a hydrofoil profile and an open center surrounded by an inner wall that defines a water flow passage; and a plurality of blade members mounted on said hub member, each blade member having two edges and extending radially outwardly from a radially inner base end thereof, at which base end each blade is mounted on said center hub member for rotation therewith to form a rotor assembly, the blade members terminating at radially outer blade tips, wherein said rotor assembly further comprises a rotor outer ring to which the blade tips are attached and which has an outer circumference that is configured for rotation within said accelerator shroud, and wherein the blade members have a chord length at their radially outer ends that is greater than the chord length at their radially inner ends; and an annular diffuser comprising a generally cylindrical ring member that has a wall cross-section comprising an asymmetrical hydrofoil shape, said annular diffuser having a diameter greater than the diameter of said accelerator shroud and being positioned behind the main accelerator shroud, in the direction of water flow through the turbine. a generally cylindrical accelerator shroud that has a length extending from the water inlet end to the water exit end and comprises a radially inner wall surface and a radially outer wall surface spaced apart from the radially inner wall surface, to form a radial wall cross-section, wherein the radially inner wall surface defines within its cylindrical cross-section a water flow area; located within the water flow area an integral hydrokinetic force-generating member, that rotates as one unit in a single direction in response to water flow in said single direction during force generation within the accelerator shroud, the integral force-generating member comprising: a center hub member having a hydrofoil profile and an open center surrounded by an inner wall that defines a water flow passage; and a plurality of blade members mounted on said hub member, each blade member having two edges and extending radially outwardly from a radially inner base end thereof, at which base end each blade is mounted on said center hub member for rotation therewith to form a rotor assembly, the blade members terminating at radially outer blade tips, wherein a center hub member having a hydrofoil profile and an open center surrounded by an inner wall that defines a water flow passage; and a plurality of blade members mounted on said hub member, each blade member having two edges and extending radially outwardly from a radially inner base end thereof, at which base end each blade is mounted on said center hub member for rotation therewith to form a rotor assembly, the blade members terminating at radially outer blade tips, wherein said rotor assembly further comprises a rotor outer ring to which the blade tips are attached and which has an outer circumference that is configured for rotation within said accelerator shroud, and wherein the blade members have a chord length at their radially outer ends that is greater than the chord length at their radially inner ends; and an annular diffuser comprising a generally cylindrical ring member that has a wall cross-section comprising an asymmetrical hydrofoil shape, said annular diffuser having a diameter greater than the diameter of said accelerator shroud and being positioned behind the main accelerator shroud, in the direction of water flow through the turbine.