HD-4 or Hydrodome number 4 was an early research hydrofoil watercraft developed by the scientist Alexander Graham Bell. It was designed and built at Bell's Beinn Bhreagh laboratory near Baddeck, Nova Scotia. In 1919 it set a world marine speed record of 70.86 miles per hour (114.04 km/h) that remained unbroken for two decades. (Source: Wikipedia)
The HD-4 incorporated all that had been learned from the successes and mishaps of its predecessors. It was a sleek gray giant with a cigar-shaped hull sixty feet long, riding on two sets of reefing hydrofoils forward and one aft. On each side was a small hull attached to a solid, streamlined outrigger, for balance while floating at rest. Each outrigger also carried a motor and aerial propeller. Later, a spray shield on each side was tapered from the outrigger hulls to the nose, giving a winged look to the craft and in fact contributing some additional aerodynamic lift. The navy could not or would not furnish the promised Liberty engines, and even the two 2 5o-horsepower Renault engines it sent did not arrive until July 1918. (By then someone had suggested that "HD" stood for "Hope Deferred.") So the first trials did not begin until October 1918.
With the Renault engines, the top speed was only 54 miles per hour. Nevertheless, the HD-4 performed well, rising easily, accelerating rapidly, taking wave without difficulty, steering well, showing good stability. Bell's proud report to the navy early in 1919, along with the postwar availability of Liberty engines, moved the navy at last to send two 350-horsepower Liberties in July 1919. With these powering its two aerial propellers, the HD-4 on September 9, 1919, set a world's marine speed record of 70.86 miles per hour, a record that stood for ten years.
In the fall of 1921 [a year before Bell's death at the age of 75], the HD-4 was dismantled. Its big gray hull lay un-regarded for decades on the shore at Beinn Bhreah. (Source: Alexander Graham Bell and the Hydrofoils)