Man operating water tricycle, probably early 20th Century
A Hydrobike brand hydrocycle
A hydrocycle is a bicycle-like watercraft, and the name was already in use in the late 1890s. Power is collected from the rider via a crank with pedals, as on a bicycle, and delivered to the water or the air via a propeller. Seating may be upright or recumbent, and multiple riders may be accommodated in tandem or side-by-side.Buoyancy is provided by two or more pontoons or a single surfboard, and some have hydrofoils that can lift the flotation devices out of the water. Brand names include Seacycle, Hydrobike, Water bike, Seahorse(Cross Trek) and itBike. Kits exist to convert an existing bicycle into a hydrocycle temporarily.
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^Oxford English Dictionary. "hydrocycle n. [cycle n. 11] a velocipede adapted for propulsion on the surface of water. 1898 River & Coast 9 July 13/1 One of the most interesting items was the Hydrocycle versus Skiff Race."