There is described a method for controlling the deformation of a surface of a sail (1) of a sailing boat (100) during a direction change manoeuvre, said method comprising the step of arranging at least one inflatable batten (10) into a respective seat (3) formed on a side surface (2a) of the sail (1), said at least one batten (10) being inflated at a predetermined working pressure, said working pressure being such as to impart to said at least one batten (10) a bending stiffness having, with no bending load, a predetermined value and the step of carrying out a manoeuvre for changing the direction of the sailing boat (100), wherein in a first part of said manoeuvre said at least one batten (10) is subjected to the action of an increasing bending load and in a second part of said manoeuvre, said bending load ends its action on said at least one batten (10), during said manoeuvre the mechanical properties of said at least one batten (10) being changed so that as said bending load increases in said first part of the manoeuvre, the value of the bending stiffness of said at least one batten (10) decreases considerably, and as the action of said bending load ends in said second part of the manoeuvre, the bending stiffness of said at least one batten (10) returns to said predetermined value. Such method is carried out by using a sail (1) provided with at least one batten (10) comprising a fluid impervious wrapping (31) adapted to be inflated by a fluid under pressure and a reinforcing structure (33) associated externally with said wrapping (31) and comprising a plurality of reinforcing thread-like elements (34a, 34b) arranged crossed with an angle comprised between about 65° and about 115°.