Junk rig refers to a sail design in which battens, strips of material like wood and fiberglass, are stretched across the entire sail from side to side. It is also called a Sampan sail or a Chinese lugsail. These designs have several advantages over other modern sails, including ease of installation and use and a cheaper price tag. Almost any modern sailing rig can be converted into a junk rig. It is especially useful when sailing on the open ocean, an activity known as blue water sailing.
Though the junk rig may appear complex, the structure is fairly simple and closely resembles the initial design that originated in ancient China. Among its recognizable features are the battens that stretch from luff, the forward edge of the sail, to leech, the rear edge of the sail. Horizontal sailcloth panels are contained between the battens. At the head, or top, of the rig is the yard, and the boom is located at the bottom. The yard and boom are similar to battens but have a thicker and sturdier composition which allows them to support the entire weight of the rig.
The mast, the vertical pole supporting the rig's configuration, is situated near the rig's forward edge, its luff. Controlling lines are attached to the rig's trailing edge, or leech. Unlike other modern rigs, a controlling line connects to each batten. If a tear forms in a sailcloth panel, the battens prevent the damage from spreading to the other panels, allowing them to function normally.
The junk rig is ideal for cruising, especially on the open ocean. The rig requires little to no adjustment from the sailor and can align itself accordingly. Its ability to sail with the wind, called running, is the biggest advantage of the junk rig. The rig's large surface area gathers the wind and propels the vessel to speeds that are achieved by only a few other rigs.
The design is not as suited for a close haul, where the vessel attempts to travel as close to the wind as possible. The combination of the sail's surface area, flatness, and low elasticity prevent the rig from reaching the speed and power of other vessels. This disadvantage also becomes apparent when trying to sail perpendicular to the wind, called reaching. These problems, however, are mostly associated with low-wind environments and can be rectified.