GYBING, the act of shifting a boom-sail from one side of the mast to the other.
In order to understand this operation more clearly, it is necessary to remark, that by a boom-sail is meant any sail, the lowest part of which is extended by a boom, and the fore-end hooked to its respective mast, so as to swing occasionally on either side of the vessel, describing an arch, of which the mast is the centre. As the wind or the course changes, it also becomes frequently necessary to change the position of the boom, together with its sail, which is accordingly shifted to the other side of the vessel, as a door turns upon its hinges. The boom is pushed out by the effort of the wind upon the sail, and is restrained in a proper situation by a strong tackle communicating with the vessel's stern.