Since the density of water is 840 times the density of air, the foils needed to lift the vessel are much smaller than those needed to lift an airplane. More water will run over and under the foil than air possibly could. A large hydrofoil can weigh up to 305 tonnes while offering about half the resistance of a planing boat. Hydrofoils can attain speeds of up to 20 to 30 metres per second. Many hydrofoils have found a place in the tourism industry and are also used in the Navy.
Sailboats are another specimen of aerodynamic engineering.
A sail is like a hollow foil that lies in a vertical plane. With the push of airflow sailboats can reach tremendous speeds and at certain 'points of sail' they can even exceed the speed of the wind that moves them. At each different point of sail the boat has a different velocity. The fastest points are at the close reaches and it is at these points when the boat is capable of travelling faster than the wind. This odd observation is due to the same concepts that were discussed about the air and hydro foils.