The Patent Office issued over 800 patents for paddle wheels, propellers, and other propulsion apparatus between 1790 and 1873. About 250 of these were propellers.
Jackson Harrington and Francis Caffrey, then of New Haven, Connecticut, patented a six-bladed propeller design in 1866 that aimed to "enlarge the driving-surface" of the propeller "by means of parallel blades with an aperture between them." Nine years later, Harrington, now living in the town of Groton Bank outside New London, patented an improvement to his and Caffrey's earlier design. The new propeller still had six blades, but instead of grouping them in pairs around a single hub, he specified that three go on a forward hub and three on a rear hub. This arrangement aimed to make the propeller easier and cheaper to manufacture. Harrington further refined the shape of the blades and their positions relative to each other, toward the end of reducing friction between propeller and water.
Harrington, born in 1827, and Caffrey, born in 1828, were both machinists.
Jackson Harrington, Screw-Propeller, U.S. patent no. 162,063, Apr. 13, 1875.
Jackson Harrington and Francis Caffrey, Propeller-Wheel, U.S. patent no. 53,297, Mar. 20, 1866.
1880 United States Census, NARA film no. T9-0106, 185A and T9-0107, 44A.