They could support the weight of a human rider and hover him several inches above the ground on a mysterious cushion of invisible magnetic energy. They could even hover over water. Although they looked pretty convincing in the movie, the hoverboards were simply wooden props attached to the actors feet. To make the boards fly, the actors were suspended by cables. A 6 horsepower 4-stroke gasoline engine spins a 5 bladed propeller to force air under the craft.
Some air is diverted into a flexible skirt around the perimeter of the craft.
The skirt is a type of air bag which helps to trap air under the craft to increase efficiency and hover higher. The higher it can hover, the better it can pass over obstacles. This is especially helpful over terrain that is not completely flat. There is a slight gap between the flexible skirt and the surface while its hovering. When hovering, the craft is virtually friction free and only requires a small thrust to move at high speeds.