On May 22, 1849, Abraham Lincoln received Patent No. 6469 for a device to lift boats over shoals.
Lincoln's idea was to allow larger ships with deep hull to reach smaller towns in shallow areas of rivers. The inflatable devices on ships would allow them to float over shoals to reach these small towns and increase trade. Lincoln could find no funding for this idea and it fell by the wayside. Lincoln is the only US president to be awarded a patent.