He won two gold medals in the only motor boat competitions included in the Olympics as helmsman of the Gyrinus II, which was designed by his father Sir John Isaac Thornycroft.
Gyrinus was the earliest round-bilge Semi-Planing Mono-Hull ('SPMH') designed by Sir John Isaac Thornycroft FRS, the great Victorian engineer, previously the designer and builder of the world's first torpedo boats and torpedo boat 'Destroyers'.
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Thornycroft was born in Chiswick in 1872 and was the eldest son of Sir John Isaac Thornycroft, the founder of the Thornycroft shipbuilding company.