A floating screw turbines device with adjustable rear deflectors/diffusors (80, 90), where the said device consists of: - three pontoons (10, 20, 30) spaced apart and fixed to the deck frame; where the left water duct is situated between the left pontoon and the central pontoon, and where the right water duct is situated between the central pontoon and the right pontoon; - each of the said water ducts (40, 50) is fixed to the deck frame and to the adjacent pontoons (10, 20; 20, 30) via duct holders (41, 51) respectively; - the left screw turbine is fixed within the left water duct by a pair of turbine shaft holders holding the left turbine shaft at its ends; and the right screw turbine which is fixed within the right water duct by a pair of turbine shaft holders holding the right turbine shaft at its ends; where turbine shaft holders (62, 72) are fixed to the deck frame; - wherein the left screw turbine and the right screw turbine are mounted in corresponding ducts (40, 50) forming a V turbines formation, where the turbine shafts (61, 71), when extrapolated, intersect at the point situated at the centre plane of symmetry which passes through the central axis of the central pontoon and is perpendicular to the water surface; and where the said turbine shafts (61, 71) are situated parallel to the water surface and are both inclined by the same angle relative to the central pontoon; the said screw turbines (60, 70) have mirror symmetrical pitch of the screws measured in regard to the centre plane of symmetry; characterized by - each of the said water ducts (40, 50) have, at the water outlet behind the corresponding turbines (60, 70), a corresponding deflector/diffusor (80, 90) connected by a set of hinges (81, 91) to the corresponding deflector/diffusor connection line (82, 92) situated at the bottom of the corresponding water duct (40, 50); - wherein the said left deflector/diffusor connection line is parallel to the left turbine shaft, and the said right deflector/diffusor connection line is parallel to the right turbine shaft, the said deflector/diffusor connection lines (82, 92), when extrapolated, intersect at the point situated at the centre plane of symmetry; and - the said deflectors/diffusors (80, 90) being capable of rotating around their corresponding connection lines (82, 92), thus affecting the water flow velocity across water ducts (40, 50) by controlling their relative pitch with respect to the floors of the water ducts (40, 50). - three pontoons (10, 20, 30) spaced apart and fixed to the deck frame; where the left water duct is situated between the left pontoon and the central pontoon, and where the right water duct is situated between the central pontoon and the right pontoon; - each of the said water ducts (40, 50) is fixed to the deck frame and to the adjacent pontoons (10, 20; 20, 30) via duct holders (41, 51) respectively; - the left screw turbine is fixed within the left water duct by a pair of turbine shaft holders holding the left turbine shaft at its ends; and the right screw turbine which is fixed within the right water duct by a pair of turbine shaft holders holding the right turbine shaft at its ends; where turbine shaft holders (62, 72) are fixed to the deck frame; - wherein the left screw turbine and the right screw turbine are mounted in corresponding ducts (40, 50) forming a V turbines formation, where the turbine shafts (61, 71), when extrapolated, intersect at the point situated at the centre plane of symmetry which passes through the central axis of the central pontoon and is perpendicular to the water surface; and where the said turbine shafts (61, 71) are situated parallel to the water surface and are both inclined by the same angle relative to the central pontoon; the said screw turbines (60, 70) have mirror symmetrical pitch of the screws measured in regard to the centre plane of symmetry; characterized by - each of the said water ducts (40, 50) have, at the water outlet behind the corresponding turbines (60, 70), a corresponding deflector/diffusor (80, 90) connected by a set of hinges (81, 91) to the corresponding deflector/diffusor connection line (82, 92) situated at the bottom of the corresponding water duct (40, 50); - wherein the said left deflector/diffusor connection line is parallel to the left turbine shaft, and the said right deflector/diffusor connection line is parallel to the right turbine shaft, the said deflector/diffusor connection lines (82, 92), when extrapolated, intersect at the point situated at the centre plane of symmetry; and - the said deflectors/diffusors (80, 90) being capable of rotating around their corresponding connection lines (82, 92), thus affecting the water flow velocity across water ducts (40, 50) by controlling their relative pitch with respect to the floors of the water ducts (40, 50).