One important period of development began with the rise of American commerce. Just after the close of the War for Independence, it was found that deep-water ships could be built of New England timber for thirty-five dollars per ton, rated tonnage, while a vessel of the same burden built in Europe cost about forty-five dollars per unit of tonnage. Two types of vessels came into use—one, the clipper ship with square sails, was used for long ocean voyages; the other, the schooner, with fore-and-aft rigging, was employed mainly in the coast-trade.
A SQUARE-RIGGED SHIP—A TYPE NOW BEING REPLACED BY FORE-AND-AFT RIGGED SCHOONERS
In speed and ease of management these vessels surpassed anything that had ever sailed. In time they became the standards for the sailing-vessels of all the great commercial nations. The types of the vessels are still standards.
THE DEVELOPMENT OF THE MODERN STEAMSHIP
The Development of the Steamship.—Another important era in ocean commerce began when steam was used as a motive power for vessels. The first deep-water vessel thus to be propelled was the Savannah. Her steam-power was merely incidental, however, and her paddle-wheels were unshipped and taken aboard when there was enough wind for sailing. Up to 1860 almost all the ocean steamships were side-wheelers, propelled by low-pressure beam-engines.
The next most important improvement was the screw-blade propeller, placed astern. This means of propulsion called for higher speed of the engines, and in a very short time compactly built high-pressure engines took the place of the low-pressure engine with its heavy walking-beam. The latter carried steam at a pressure varying from twenty to thirty-two pounds; the modern boiler has steam at 260 pounds per square inch.