Miss Britain III is a racing power boat designed and built by Hubert Scott-Paine, a British aircraft and boat designer.
During 1932 Hubert Scott-Paine, owner of the British Power Boat Company and already a noted power boat racer, asked Rolls-Royce for a (2,500 hp) Rolls-Royce 'R' engine which had powered the winning Supermarine S6B entrant in the 1931 Schneider Trophy challenge. He was planning a single-engined challenge to Garfield 'Gar' Wood who held the Harmsworth Trophy with his Miss America X speedboat, a monster of 38 ft (12 m) with 4 engines totalling 7,800 horsepower. No engine was then available so there the matter rested.
In February 1933, with the success of his Power-Napier engine to which he had exclusive rights, Scott-Paine issued his challenge for the Harmsworth Trophy. Within a period of less than ten weeks he had designed and built Miss Britain III in conditions of great secrecy at his Hythe workshops. The result was revolutionary, with stringers of metal-reinforced wood and aluminium cladding, a single 1,350 horsepower (1,010 kW) Napier Lion VIID engine, and a length of only 24-foot-6-inch (7.47 m) The attention to detail is evident in the thousands of duralumin countersunk screws with the slots all in line with the water or air flow. George Selman, one of the country's leading propellor experts, designed a new propellor after the existing designs proved unsatisfactory. Testing was carried out in great secrecy on Southampton Water in the early dawn.
The team sailed for America in August 1933 and the contest was held on the St. Clair River at Algonac, Michigan on 4 September. The David and Goliath contest was very closely fought but Gar Wood managed to win by a small margin - average speed 86.937 mph (139.912 km/h) against 85.789. Scott-Paine returned to Britain to a hero's welcome.
Following a fire on board which was quickly put out and the boat repaired, a record breaking attempt was made on 16 November 1933 on Southampton Water. Scott-Paine and Gordon Thomas became the first men to travel at over 100 mph (160 km/h) in a single-engined boat, and this record remained for 50 years.
Miss Britain III was taken to Venice in 1934 where Scott-Paine won both the Prince of Piedmont's Cup and the Count Volpi Trophy, setting a world record for a single-engined boat of 110.1 mph (177.2 km/h) in salt water.
In 1951 Scott-Paine presented Miss Britain III to the National Maritime Museum where it remains on view.