"Whaleback" Chinese Junks

A sha-ch'uan or sand boat. The big basket tied to the house side is not a dinghy: it's a sea anchor. Illustration by Valentin A. Sokoloff. Click any image to enlarge.

Some aspects of the design and construction of Chinese junks are pretty familiar: one the best known is the use of numerous bulkheads rather than frames to provide transverse strength and divide the vessel into a series of watertight compartments. Others are the lifting or retractable rudder, and of course the fully-battened lugsails that are almost synonymous with the term "junk." One design and construction element that is not so well known, though, is the whaleback shape of the hull on many junks. 

One type exhibiting the whaleback was the sha-ch'uan, or sand boat, which was in use well into the 20th century. These bluff-bowed Kiangsu traders typically measured 85' LOA and 18.5' beam, and were distinct from larger traders of the same port by generally finer lines. 

Sail plan and interior arrangements of a sha-ch'uan by G.R.G. Worcester. (Please excuse distortion at the bow, due to tight binding on the book from which the image was scanned.)

Among the more obvious features of  the sha-ch'uan is the five-masted rig, in which only two of the masts were stepped along the vessel's centerline, and all of which were raked at different angles, so that they were splayed like the fingers of an open hand. The two drawings above show different sail types: only the mainmast carries the familiar fully-battened Chinese lugsail in Worcester's line drawing, while Sokoloff's watercolor shows that type of sail on four of the five masts. 

Cross-section of sha-ch'uan. Note the use of frames along with the bulkheads to provide transverse strength. Illustration by Sokoloff.

Cross-section of  sha-ch'uan. Illustration by Worcester.

Sokoloff surely based his color cross-section on Worcester's. Both show the whaleback structure, in which the hull-proper angles sharply inboard from a chine that is well above the waterline and might almost be called a sheerline. Worcester calls this top surface a "guard deck," but from a construction standpoint, it's really the upper surface of an all-around hull, like that of a submarine's (although it is pierced by numerous hatches). The main deck is added atop the guard deck, and there are planks, apparently enclosing dead space, that fill the gap between the guard deck and the overhanging ends of the main deck.

With its extreme tumblehome, the whaleback junk seems to give up a lot of storage capacity compared to Western ship design, in exchange for superior safety. Should the junk's entire upper deck and house be swept away, its hull would remain intact and enclosed. There were numerous incidents of Western-style wooden ships losing their houses in storms and sinking as a result.

Although the sha-ch'uan had no backbone, it did have a substantially thicker central plank that provided some longitudinal strength (and some lateral plane), aided by several half-round wales along the sides and three timbers running full-length along the top surface of the guard deck at both sides of the hatches. Rising well above the waterline was a false stern that extended 7 feet aft of the hull proper, and beyond that was a 10-foot-long stern gallery.

The sha-ch'uan was by no means the only whaleback junk. Two more are shown below, and Worcester's book contains many other examples.

Although its built-up gunwales make it less obvious than on the sha-ch'uan, the shaohing-ch'uan, or Hangchow Bay Trader, also had whaleback construction. Illustration from Worcester. 

In contrast to the preceding image, the whaleback construction of this vessel is entirely obvious, its deck being far narrower than that of either the sha-ch'uan or the shaohing-ch'uan. Very heavy wales just below the sheer-chine add great strength to the structure. I have no information on the vessel type, identified by artist/author Bjorn Llangstrom only as being a warship similar to that upon which Marco Polo returned home to Europe. 

Sources: 
The Junks and Sampans of the Yangtze, G.R.G. Worcester, 1971, Naval Institute Press
Ships of China, Valentin A. Sokoloff, 1982, Sokoloff
The Quest for India, Bjorn Llandstrom, 1964, Allen & Unwin