A Medium clipper is a type of clipper designed for both cargo carrying capacity and speed. An evolutionary adaptation of the extreme clipper, the medium clipper had been invented by 1851, when the hull type appeared in U.S. shipyards. Medium clippers continued to be built until 1869, when the Glory of the Seas, one of the last known medium clipper ships to be built, was launched by the firm of Donald McKay & Co.
As these precious metal mining activities matured, the working populations of the affected gold and silver mining belts began to demand large quantities of manufactured goods. Shippers began to look for a ship design that would speed large quantities of boxed, barrelled, or crated cargo to Melbourne or San Francisco.
At the beginning of the 1850s, the dominant U.S. fast sailing ship design was the extreme clipper, properly defined as a cargo vessel with a 40-inch-or-more dead rise at half floor. This refers to a sail-powered cargo hull with a relatively flat-floored rear half, tapering as one moves forward along the hull to a relatively sharp forward half.
Extreme clippers successfully served the 49ers who reached California placer fields during the opening years of the rush, but negative aspects of the design soon became apparent. The sharp-floored forward halves could not carry as much cargo as a full flat hull. In addition, the sharp-floored forward halves lacked the buoyancy of the rounded rear halves, and this asymmetrical buoyancy tended to strain and weaken the hull. The working lifespan of an extreme clipper ship tended to be short.
By 1852 U.S. shipbuilders such as Donald McKay had begun to develop a new type of clipper ship hull, which combined a flat-floored hull for maximal cargo capacity with a clipper bow resembling that of the extreme clipper chip. The stern, masts, spars, and sail area also resembled the extreme clipper ship. The half floor dead rise of the true extreme clipper ship was, however, no longer to be seen.
Period of design
In 1851, shipbuilders in Medford, Massachusetts built the Antelope. Often called the Antelope of Boston to distinguish it from other ships of the same name, this vessel is sometimes called one of the first medium clipper ships. A ship-design journalist noted that "the design of her model was to combine large stowage capacity with good sailing qualities." The Antelope was relatively flat-floored and had only an 8-inch dead rise at half floor.
Shippers responded positively to the new hull design and instructed shipbuilders accordingly. By 1854, the numbers of medium clippers on the stocks were far outpacing the remaining extreme clippers. The last true extreme clipper was built in 1855.
By the 1860s, the time of the medium clipper was also coming to an end. Construction of a network of coaling stations around the world was making it possible for ocean-going steamships to cover global trade routes with a speed, frequency, and reliability of service that no medium clipper ship could match.
In the 1860s a final generation of clipper ships, the clipper-built composite ship, featured wooden planking over a wrought iron frame; the strength of the iron frame protected the composite clipper from the hogging and sagging that had bedevilled its predecessor, the extreme clipper. The surviving clipper ships of the world as of 2015, such as the Cutty Sark, are clipper-built composite ships; no true extreme clipper or medium clipper ships are known to survive.
- Boston Daily Atlas, March 6, 1851
- "Clipper ships", Stoddart's Encyclopaedia Americana; a dictionary of arts, sciences, and general literature, and companion to the Encyclopaedia Britannica. American Supplement. (9th ed.), 2, New York, Philadelphia: J.M. Stoddart, 1884, p. 151
- Boston Daily Atlas, December 29, 1852
- Boston Daily Atlas, November 29, 1851