The junk is a classic Chinese sailing vessel of ancient unknown origin, still in wide use. Junks were developed during the Han Dynasty (206 BC–220 AD) and were used as seagoing vessels as early as the 2nd century AD. They evolved in the later dynasties and further evolved to represent one of the most successful ship types in history. They were found, and in lesser numbers are still found, throughout South-East Asia and India, but primarily in China, perhaps most famously in Hong Kong.
High-sterned, with projecting bow, the junk carries up to five masts on which are set square sails consisting of panels of linen or matting flattened by bamboo strips. Each sail can be spread or closed at a pull, like a venetian blind. 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 structure and flexibility of junk sails make the junk easy to sail, and fast. The Chinese junk ship possessed many technical advances in hull design and sail plan along with the creation and use of the rudder which would influence how Europeans would design their own ships in the future. The junk ship at the time may have been the fasted ship ever built in the ancient world.
The mounted steering rudder permitted the steering of ships which were huge, high freeboard ones and its good designs allowed modification to the depth of the water that was later used in the theories of Westernized ship building. Freeboard in a nautical term used to describe the distance from the boat or ship’s upper deck level to the distance of the waterline measured at the lowest point where water can come into the boat or ship. In China, the rudders were attached to the hull by way of wooden sockets while ordinarily the larger ones were suspended from above by a rope tackle system so that they could be lowered or raised into the water. A sizable junk can have a rudder that needs up to three members of the crew to control in strong weather helm. The Chinese junks also included the fenestrated rudders which had holes in order for better control. This was another innovation adopted into early 20th century Western naval technology systems which helped to make torpedo boats maneuverable.
Traditionally, the hull has a horseshoe-shaped stern supporting a high poop deck. The bottom is flat in a river junk with no keel, so that the boat relies on a dagger-board, lee-board or very large rudder to prevent the boat from slipping sideways in the water. The hull is partitioned by solid bulkheads running both transversely and longitudinally, adding greatly to strength. 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. Junks have narrow waterlines which accounts for their speed in moderate conditions. The largest junks, the treasure shipscommanded by 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, based on the size of the rudder post that was found.
Chinese junks were used extensively in Asian trade during the 16th and 17th century, especially to Southeast Asia and to Japan, where they competed with Japanese Red Seal Ships, Portuguese carracks and Dutch galleons.