A method of reducing vibration in a rotary system (120, 130, 140) of a watercraft, for example a cargo ship (100), comprising balancing said rotary system (120, 130, 140), characterized by providing a rotational element (300, 302-306) comprising a chamber (310-312) having a fulcrum on a rotational axis (340) of said rotational element (300, 302-306), comprising a circumferential balancing area (320) and being partially filled with an amount of a thixotropic balancing substance (330). A corresponding apparatus and system.