Abstract: A system for adjusting spreaders and diamonds on sailing boats, the system being adapted to provide spreaders or diamonds which are adjustable on the water thus allowing the craft's crew greater control of the sailing rig. The system has a pair of spreader arms pivotally connected to a pair of control arms attached to a mast. The spreader arms are adjustable by means of a halyard which runs via the control arms to distal ends of the spreader arms. The spreader arms have a number or holes or slots proximate their distal ends to receive respective port and starboard stays of the sailing craft. Depending on prevailing wind conditions, the spreader arms may be selectively pivoted forward towards the control arms by a pulling force applied to the halyard. In this way, the shape and bend characteristics of the mast may be altered by the crew so as to control the amount of draft in the sails and to affect the amount of power generated by the sailing rig.