A safety system of a harness, in particular of the trapezoidal type, is suitable for use on watercraft such as a yacht or windsurfer. A basic element (10) is coupled to the harness. A hook (15), suitable for being hooked by a cable, is coupled to the basic element (10). The basic element (10) has a first piece (31) connected to the harness and a second piece (30, 15) that can be disconnected from said first piece (31). The first piece (31) is coupled to the second piece (30, 15) by a coupling (32) that can be removed.