Most boats cannot travel very fast because they have to force their hulls through the water. Hydrofoils, which can carry people at speeds of 80 km/h (50 mph) an hour or more, overcome this problem. At rest, a hydrofoil looks much like any other boat. But beneath the hull are winglike foils, which rise as the hydrofoil begins to move through the water. As the speed increases, the foils lift the hull of the boat clear above the surface, and it can then quickly accelerate to a high speed.