Abstract: A device for avoiding capsizing of catamarans, in which a mast of the catamaran is pivotally mounted on a transverse beam of connection between two hulls and kept in position by two shrouds which, starting from the top of the mast and winding around tensioning pulleys and positioning pulleys, are connected to a movable point of a piston device, which is of the oleodynamic-mechanical type and generally comprises a piston head kept in position in a cylinder by resiliency and made of two parts connected to each other by a calibrated helical spring. A pipe with a pump and unidirectional valves and for the oil of the oleodynamic device are provided outwardly of the cylinder. When the load on the mast exceeds the value of calibration of the spring, the piston head opens to uncover apertures for the passage of the oil which in this manner circulates and permits shifting of the piston head in the cylinder. The mast only bends if the wind acting on the sail exceeds the calibration value of the spring.