Junk is a type of ancient Chinese sailing ship that is still in use today. Junks were used as seagoing vessels as early as the 2nd century AD and developed rapidly during the Song dynasty (960–1279). They evolved in the later dynasties, and were used throughout Asia for extensive ocean voyages. They were found, and in lesser numbers are still found, throughout South-East Asia and India, but primarily in China. Found more broadly today is a growing number of modern recreational junk-rigged sailboats.
The term junk may be used to cover many kinds of boat—ocean-going, cargo-carrying, pleasure boats, live-aboards. They vary greatly in size and there are significant regional variations in the type of rig, however they all employ fully battened sails. The term junk (Portuguese junco; Dutch jonk; and Spanish junco) was also used by European explorers for large unrelated native Austronesian warships, like the Philippine karakoa and the Maluku kora kora.
The term may stem from the Chinese chuán (船, "boat; ship"), also based on and pronounced as [dzuːŋ] (Pe̍h-ōe-jī: chûn) in the Min Nan variant of Chinese, or zhōu (舟), the old word for a sailing vessel. Junk entered the English language in the 17th century through the Portuguese junco from the Malay jong or Javanese djong. The modern Standard Chinese word for an ocean-going wooden cargo vessel is cáo (艚). Views diverge on whether the origin is from a dialect of Chinese; Pierre-Yves Manguin, amongst others, points to an Old Javanese origin, the word jong can be traced from an old Javanese inscription in the 9th century. It entered Malay language by 15th century, when a Chinese word list identify it as Malay word for ship. The Malay Maritime Code, first drawn up in the late 15th century, uses junk frequently as the word for freight ships. European writings from 1345 through 1601 use a variety of related terms, including jonque (French), ioncque (Italian), iuncque (Spanish), and ionco (Dutch).
The historian Herbert Warington Smyth considered the junk as one of the most efficient ship designs, stating that "As an engine for carrying man and his commerce upon the high and stormy seas as well as on the vast inland waterways, it is doubtful if any class of vessel… is more suited or better adapted to its purpose than the Chinese or Indian junk, and it is certain that for flatness of sail and handiness, the Chinese rig is unsurpassed."
The structure and flexibility of junk sails make the junk fast and easily controlled. The sails of a junk can be moved inward toward the long axis of the ship. In theory this closeness of what is called sheeting allowed the junk to sail into the wind. In practice, evidenced both by traditional sailing routes and seasons and textual evidence junks could not sail well into the wind.
Classic junks were built of softwoods (although after the 17th century of teak in Guangdong) with the outside shape built first. Then multiple internal compartment/bulkheads accessed by separate hatches and ladders, reminiscent of the interior structure of bamboo, were built in. Traditionally, the hull has a horseshoe-shaped stern supporting a high poop deck. The bottom is flat in a river junk with no keel (similar to a sampan), so that the boat relies on a daggerboard, leeboard or very large rudder to prevent the boat from slipping sideways in the water. Ocean-going junks have a curved hull in section with a large amount of tumblehome in the topsides. The planking is edge nailed on a diagonal. Iron nails or spikes have been recovered from a Canton dig dated to circa 221 BC. For caulking the Chinese used a mix of ground lime with Tung oil together with chopped hemp from old fishing nets which set hard in 18 hours, but usefully remained flexible. Junks have narrow waterlines which accounts for their potential speed in moderate conditions, although such voyage data as we have indicates that average speeds on voyage for junks were little different from average voyage speeds of almost all traditional sail, i.e. around 4–6 knots. The largest junks, the treasure ships commanded by Ming dynasty Admiral Zheng He, were built for world exploration in the 15th century, and according to some interpretations may have been over 120 metres (390 ft) in length, or larger. This conjecture was based on the size of a rudder post that was found and misinterpreted, using formulae applicable to modern engine powered ships. More careful analysis shows that the rudder post that was found is actually smaller than the rudder post shown for a 70' long Pechili Trader in Worcester's "Junks and Sampans of the Yangtze".
Another characteristic of junks, interior compartments or bulkheads, strengthened the ship and slowed flooding in case of holing. Ships built in this manner were written of in Zhu Yu's book Pingzhou Table Talks, published by 1119 during the Song dynasty. Again, this type of construction for Chinese ship hulls was attested to by the Moroccan Muslim Berber traveler Ibn Battuta (1304–1377 AD), who described it in great detail (refer to Technology of the Song dynasty). Although some historians have questioned whether the compartments were watertight, most believe that watertight compartments did exist in Chinese junks because although most of the time there were small passageways (known as limber holes) between compartments, these could be blocked with stoppers and such stoppers have been identified in wrecks. All wrecks discovered so far have limber holes; these are different from the free flooding holes that are located only in the foremost and aftermost compartments, but are at the base of the transverse bulkheads allowing water in each compartment to drain to the lowest compartment, thus facilitating pumping. It is believed from evidence in wrecks that the limber holes could be stopped either to allow the carriage of liquid cargoes or to isolate a compartment that had sprung a leak.
Benjamin Franklin wrote in a 1787 letter on the project of mail packets between the United States and France:
As these vessels are not to be laden with goods, their holds may without inconvenience be divided into separate apartments, after the Chinese manner, and each of these apartments caulked tight so as to keep out water.— Benjamin Franklin, 1787
In 1795, Sir Samuel Bentham, inspector of dockyards of the Royal Navy, and designer of six new sailing ships, argued for the adoption of "partitions contributing to strength, and securing the ship against foundering, as practiced by the Chinese of the present day". His idea was not adopted. Bentham had been in China in 1782, and he acknowledged that he had got the idea of watertight compartments by looking at Chinese junks there. Bentham was a friend of Isambard Brunel, so it is possible that he had some influence on Brunel's adoption of longitudinal, strengthening bulkheads in the lower deck of the SS Great Britain . Bentham had already by this time designed and had built a segmented barge for use on the Volga River, so the idea of transverse hull separation was evidently in his mind. Perhaps more to the point, there is a very large difference between the transverse bulkheads in Chinese construction, which offer no longitudinal strengthening, and the longitudinal members which Brunel adopted, almost certainly inspired by the iron bridge and boiler engineering in which he and his contemporaries in iron shipbuilding innovation were most versed.
Due to the numerous foreign primary sources that hint to the existence of true watertight compartments in junks, historians such as Joseph Needham proposed that the limber holes were stopped up as noted above in case of leakage. He addresses the quite separate issue of free-flooding compartments on pg 422 of Science and Civilisation in Ancient China:
More to the point wet wells were apparent in Roman small craft of the 5th century CE.