A junk is a Chinese sailing vessel. The English name comes from Malay dgong or jong. Junks were originally developed during the Han Dynasty (220 BC-200 AD) and further evolved to represent one of the most successful ship types in history.
Junks are efficient and sturdy ships that were traveling across oceans as early as the 2nd century AD. They incorporated numerous technical advances in sail plan and hull designs that were later adopted in Western shipbuilding.
The structure and flexibility of junk sails make the junk easy to sail, and fast. Unlike a traditional square rigged ship the sails of a junk can be moved inward, toward the long axis of the ship, allowing the junk to sail into the wind.
The sails include several horizontal members ("battens") which provide shape and strength. Junk sails are controlled at their trailing edge by lines much in the same way as the mainsail on a typical sailboat, however in the junk sail each batten has a line attached to its trailing edge where on a typical sailboat this line (the sheet) is attached only to the boom. The sails can also be easily reefed and adjusted for fullness, to accommodate various wind strengths. The battens also make the sails more resistant than traditional sails to large tears, as a tear is typically limited to a single "panel" between battens. Junk sails have much in common with the most aerodynamically efficient sails used today in windsurfers or catamarans, although their design can be traced back as early the 3rd century AD.
The standing rigging is simple or absent.
The sail-plan is also spread out between multiple masts, allowing for a powerful sail surface, and a good repartition of efforts, an innovation adopted in the West around 1304. The rig allows for good sailing into the wind.
Flags were also hung from the masts to bring good luck to the sailors on board. The Chinese were very superstitious, and believed a mighty dragon lived in the clouds. It is said that when the dragon gets angry, it conjures up typhoons and storms. bright flags, with chinese writing on them, was said to please the dragon. Red was the best color, when the dragon would even help the sailors.
Classic junks were built of softwoods (though in Guangdong in teak) with multiple compartments accessed by separate hatches and ladders: similar in structure to the interior stem of bamboo. The largest junks were built for world exploration in the 1400s, and were around 120 (400+ feet) meters in length.
Junks employed stern-mounted rudders centuries before their adoption in the West, though in fact the rudder origin, form and construction was completely different from that adopted in the West. It was an innovation which permitted the steering of large, high-freeboard ships, and its well-balanced design allowed adjustment according to the depth of the water. A sizable junk can have a rudder that needs up to three members of the crew to control in strong weather. The world's oldest known depiction of a stern-mounted rudder can be seen on a pottery model of a junk dating from the 100s CE, though some scholars think this may be a steering oar - a possible interpretation given that the model is of a river boat that was probably towed or poled. By contrast, the West's oldest known stern-mounted rudder can be found on church carvings dating to around 1180 CE.
Also, from sometime in the 13th-15th centuries many junks incorporated "fenestrated rudders" (rudders with holes in them), an innovation adopted in the West in 1901 to decrease the vulnerability of torpedo boat's rudders when manoeuvering at high speed. Likewise, the Chinese discovery was probably adopted to lessen the force needed to direct the steering of the rudder.
The rudder is reported to be the strongest part of the junk. In the Tiangong Kaiwu "Exploitation of the Works of Nature" (1634), Song Yingxing wrote, "The rudder-post is made of elm, or else of langmu or of zhumu." The Ming author also applauds the strength of the langmu wood as "if one could use a single silk thread to hoist a thousand jun or sustain the weight of a mountain landslide."
Leeboards & centerboards
Leeboards and centerboards, used to stabilize the junk and to improve its capability to sail upwind are documented from a 759 AD book by Li Chuan, an innovation adopted by Portuguese and Dutch ships around 1570.
Other innovations included the square-pallet bilge pump, which were adopted by the West during the 16th century. Junks also relied on the compass for navigational purposes.