Meantime Stevens, left to himself, had, in 1804, built a vessel propelled by twin screws which navigated the Hudson River. This vessel was remarkable in many ways. The boiler was tubular, and the screw was almost identical with the short four-threaded helix which many years afterwards was generally adopted. It is interesting to note that the screw propeller was tried so early, for it is generally believed that it was not used at all until many years after the introduction of paddles. The engine and boiler of Stevens’ boat are preserved at the Stevens Institute at Hoboken. After his death his son tried the engine and boiler in a boat, which, in the presence of a committee of the American Institute of New York, attained a speed of about nine miles an hour. Although the screw proved its suitability for propulsion, its superiority was not acknowledged, and for many years afterwards marine engineers confined their attention to the improvement of paddle-wheels and the engines for driving them. In 1807, with the assistance of his son Robert, Stevens built the paddle-wheel steamer _Phœnix_, which plied for six years on the Delaware. Dr. James Renwick of Columbia said that “the Stevenses were but a few days later” than Fulton “in moving a boat with the required velocity,” and that “being shut out of the waters of New York by the monopoly of Livingston and Fulton, Stevens conceived the bold design of conveying his boat, the _Phœnix_, to the Delaware by sea, and this boat, which was so near reaping the honour of first success, was the first to navigate the ocean by the power of steam.” The piston-rod of the _Phœnix_ was guided by slides instead of the parallel motion of the Watt engine, and the cylinder rested on the condenser. A point in which the superiority of the _Phœnix_ over the _Clermont_ was shown, was that the paddle-wheel of the _Phœnix_ had a guard beam, which the _Clermont_ lacked. The _Phœnix_ was taken to Philadelphia by sea by Robert Livingston Stevens, son of Robert Stevens. He was accompanied on this voyage by Moses Rogers, to whom the title of “Pioneer Steam Navigator” has been given by American historians, partly on account of this voyage and partly because he was on board the auxiliary sailing ship _Savannah_ on her memorable voyage to Europe.[16] [16] See p. 122. In 1806 Fulton returned to America, having ordered an engine to be made by Messrs. Boulton and Watt at Birmingham. He did not tell them what he proposed to do with it, but it was the engine for the first steamboat constructed by him for American voyages--the famous _Clermont_. After this engine was delivered in New York it remained in the Customs while Brownne, a shipbuilder, constructed the hull. In 1807 the boat made her first trip on the Hudson.