Isaac Thomas (Tom) Thornycroft (1881-1955)
Born the second son of Sir John Thornycroft, the founder of the engineering and boat building firm which took his name.
Tom Thornycroft’s motor boat, Gyrinus II, won both the Class B and Class C events at the 1908 Olympics against scant opposition – in fact, the only other entry in both events failed to complete the course. Gyrinus II had been designed by Tom and built in the family boatyards.
On leaving St. Paul’s School, Tom Thornycroft joined the family firm but resigned from the Board in 1934 following differences of opinion over future company policy. Many of the Thornycroft family were distinguished sculptors and following the tradition of his parents and grand-parents he became a sculptor of considerable note. Although he was never a professional yacht designer, he had much to do with the development of the Swallow class. His greatest success as a helmsman came in 1931 when he won the Prince of Wales Cup.
He was also a keen motor racer and in 1908 he placed fifth in the Tourist Trophy on the Isle of Man. Tom Thornycroft came very close to making a second Olympic appearance in 1951.
1910 Biographical information and image at Automotor Journal 19100219
At the age of 70, and 44 years after winning his two gold medals, he was an official reserve for the yachting team and although he went to Finland for the Games, he was not called on to compete.
1955 Obituary 
YACHTSMEN and yacht designers will have learned with considerable regret of the death of Mr. Tom Thornycroft, which occurred on Monday, June 6th, at his home, Tidnock Farm, Overton, Hampshire.
Mr. Thornycroft, who was the second son of the late Sir John I. Thornycroft and brother of Sir John E. Thornycroft, the governing director and chairman of John I. Thornycroft and Co., Ltd., the shipbuilders and engineers, was born at Basingstoke in November, 1881.
He was trained as an engineer and for some twenty-one years, until he severed his connection with the family business in 1934, was general manager of the motor vehicle works at Basingstoke of the company. During this time he was responsible for the design of the light cars, then manufactured by the company, and took part in many racing events and reliability trials.
Tom Thornycroft had much to do with the development of the early paraffin vaporising engine and also with the design of the Thornycroft diesel engine, which eventually superseded the earlier unit. His interest also extended to motor boats and the design of the coastal motor boats of the first world war was largely based on experiments carried out by Tom Thornycroft and his father.
All his life he was interested in small boats and yachting, and won his first prize at the age of fourteen. He was a member of several yacht clubs, including the Bembridge Sailing Club, which he joined as long ago as 1895.
However, his interest did not stop at the sailing and handling of small craft, but was extended to include their design, and although not in practice, many designs came from his drawing board, including that of his own 70-ton yacht, "King Duck," which he sailed to Helsinki to attend the 1952 Olympic Games.
1956 Obituary 
Tom Thornycroft was educated at St. Paul's School, and acquired his technical knowledge at the City and Guilds Technical College, South Kensington (then the Central Technical College, Finsbury), subsequently being employed with Vickers, Ltd., Erith.
For five years he was head of the marine motor and vehicle drawing office at J. I. Thornycroft and Company, Ltd., Chiswick, and in 1912 became general manager of their Basingstoke works, meanwhile holding the post of managing director of Venture, Ltd., Basingstoke.
He was elected a Member of the Institution in 1947, and had been a Member of the Institution of Automobile Engineers since 1934. He was also a Member of the Institution of Production Engineers.
His death occurred on 6th June, 1955, in his sixty-fourth year.