Lincoln had a life-long interest in mechanics and inventions. “Man is not the only animal who labors; but he is the only one who improveshis workmanship,” he noted in an 1858 lecture on inventions.
Lincoln, who steered flatboats down the Mississippi and Ohio Rivers in his youth, developed an idea for a device that would help lift boats over sandbars using inflatable bellows attached to the hull. Lincoln and mechanic Walter Davis developed a scale model that Lincoln used to secure Patent 6469 in 1849.
According to William Herndon, Lincoln foresaw the patent leading to a “revolution” in steamboat navigation. However, the device was impractical and, said Herndon, “was never applied to any vessel, so far as I ever learned, and the threatened revolution in steamboat architecture and navigation never came to pass.”
http://www.google.com/patents/US6469