Abraham Lincoln, the future 16^th President, observed a river boat that had run aground near his office in Springfield Il. After watching the river men unload the cargo to lighten the vessel so it could be floated off the sand bar, he returned to his office and made a model of the device he later patented. The invention added buoyancy to a riverboat which raised the hull. It could then pass through shallow waters without having to unload their cargo. 

It is not known if the device was ever actually fabricated and installed on a riverboat. However, the the Smithsonian National Museum of American History has the original patent model and provides a replica of the model for museums and traveling shows.

Mr. Lincoln is the only president to have a patent