Bell built fast hydrofoil boats

A hydrofoil is an underwater fin that resembles a ski and has a flat or curved surface that lifts a moving boat as it pushes against the water it is traveling through. Therefore, hydrofoils reduce the amount of time the boat is in contact with the water, which lowers drag at higher speeds. Despite the fact that hydrofoil designs date back to 1861, it took Italian inventor Enrico Forlanini until 1906 to build the first practical hydrofoil.

Bell and Casey Baldwin, his dependable manager, created the fastest hydrofoils between 1908 and 1920. Bell and Baldwin set out to create a "heavier than water" vehicle in 1908, when Bell was dabbling in aviation. They were probably influenced by Forlanini's work as well as the Scientific American article from March 1906 that described the fundamentals of hydrofoils. Bell and Baldwin's first hydrofoil, or "hydrobromide," the HD-1, was measured at nearly 72 km (about 45 miles) per hour in 1911. Bell and Baldwin completed the HD-4 hydrofoil in September 1919, after making a number of improvements and building two more hydrofoils. This hydrofoil set a speed record when it sped across Bras d'Or Lake in Nova Scotia at 114 km (70.8 miles) per hour.