Screw Propeller Model

Mechanical engineer Isaac Dripps donated this propeller model to the U.S. National Museum in February 1886. This model shows Dripps's six-bladed propeller design, where each blade has a turned flange at its tip to help grip the water. The blades are separate castings bolted to the central hub. Such construction was the most common way to make large propellers in the nineteenth century, as it allowed ready replacement of the easily damaged blades. Etched on one of the blades is the declaration, "This Screw Propeller was designed by and made under the directions of Isaac Dripps at Bordentown New Jersey in the Year 1840." He did not patent this propeller.

Isaac Dripps (1810-92) was a prominent railroad engineer. Born in Ireland, he arrived in the U.S. with his parents in infancy. He apprenticed to Philadelphia steamboat-engine builder Thomas Holloway in 1826 and in 1831 was hired by Robert L. Stevens to assemble the John Bull locomotive, newly delivered from England for the Camden & Amboy Railroad, although he had never seen such a machine before. He also acted as engineer for the John Bull's first trip. Dripps continued as an engineer for the Camden & Amboy until 1854, during which time he and Stevens developed the cowcatcher and the bonnet spark arrester, among other early locomotive improvements. After a short time as partner in a locomotive works, he returned to superintending motive power for railroads, ending his career with the Pennsylvania Railroad. One biography says, "In the course of his career he devised innumerable mechanisms, tools, and the like for use in the construction of locomotives, freight and passenger cars, and steamboat machinery, but never patented any of them."

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