Abstract: In a hydraulic system for roll stabilization of a vessel by motions of the rudder an arrangement for supplying a hydraulic fluid to the rudder engine comprises a constant delivery pump, a pressure accumulator, and a valve gear unit. While the valve is opened the hydraulic fluid is delivered by the pump and the accumulator, and when the valve is closed the pump fills up the accumulator to maximum working pressure. The valve gear unit comprises a proportional control valve for controlling period, direction and flow rate of the hydraulic fluid to the steering engine and a load compensation device for controlling the returning flow returning via the proportional control valve for compensating for irregular loads from the waves or the sea against the rudder.