Blanche Thornycroft (1873 - 1950)

In 1866, John Isaac Thornycroft founded his shipbuilding company on a thin strip of riverside land at Chiswick, on the banks of the River Thames in London.
Blanche Thornycroft
Blanche Thornycroft
John’s father, a well-known Sculptor, had seen 'something' in his 16-year old child which was proven as within 20-years he and his company (J.I. Thornycroft & Company) had become one of the world's most respected names in marine engineering and shipbuilding.
During the first half of the 20th century, J I Thornycroft & Company designed and built some of the most significant vessels for the Royal Navy as well as military agencies from around the world. In addition, they quickly gained a reputation for quality yachts and motor cruisers which they supplied to wealthy private customers.
Innovation and problem solving was a trait of the Thornycroft family and on this page we reflect on the contribution of a lesser known member of the family, Blanche Thornycroft, one of John’s five daughters.
In 1904, Thornycroft had made the decision to relocate the majority of the company’s shipbuilding activities to a newly acquired shipyard at Woolston, near Southampton. This also gave him the opportunity of moving his family to Bembridge, on the Isle of Wight.
Despite the business pressure of big shipbuilding contracts, John Thornycroft maintained his first love, a keen interest in ship design. Sitting at a drawing board to stimulate this passion and having recognised the importance of the testing scale models and new designs, he took the move of house as an opportunity to create an unusual test facility in the very heart of his new home.
Lily Pond
Sir John at the Lily Pond (Pumps and various apparatus were hidden in the shed)
Known as ‘The Lily Pond’ Thornycroft integrated a model ship test tank into the landscaped outdoor decorative water system. Once the waterfall was turned off and the water had time to settle, a model hull or vessel could be towed across the surface at a constant speed, pulled by a controlled descending weight.
One could say that this was akin to today’s man cave although Thornycroft had a special member on his team, his 31-year old daughter, Blanche Coules Thornycroft.
Blanche was born in Hammersmith on 23rd December 1873, and whilst her four sisters (Edith Alice, Mary Beatrix, Ada Francis, and Eldred Elizabeth) enjoyed the social life associated with their family wealth, Blanche seemed most happy with a pencil and note pad, calculating endless mathematical puzzles and conundrums.
She showed little interest in the usual teenage pursuits, spending her time reading books, sketching endless shapes and calculating angles. It is not clear however, where she acquired her knowledge of engineering as there is no record of any formal university education.
Whilst her two brothers (John Edward & Isaac Thomas) both played active roles in the company, her four female siblings are not known to have had any involvement.
Test tank
Test Tank built at the family home in Bembridge c1911
In 1909, recognising the limited capabilities of ‘The Lily Pond’, Civil Engineering firm L.G. Mouchel were commissioned to design and build an experimental boat tank testing facility.
Thornycroft spent endless hours testing, adjusting and developing hull shapes and keel designs.  Throughout this process, he had the benefit and assistance of Blanche, a key assistant throughout much of this testing.
Blanche at work
Blanche at work
Although never appearing officially on the company payroll, it is believed that Blanche worked tirelessly as an apprentice to her Father, who held her maths skills in very high regard.
The actual date of when she finished her education and started to work for the Thornycroft Company is not known, although it is understood that the family archive hold a number of her notebooks from the latter part of the 19th century, as do The Classic Boat Museum at East Cowes.
Tom Thornycroft
Tom Thornycroft with Gyrinus II
Some of the early work Blanche was involved in was the development of streamlined hull-forms for racing boats and she was directly involved in the design of Gyrinus II, in which her brother Tom (pictured) won two Olympic Gold Medals in London in 1908.
J.I. Thornycroft & Company became world renowned for their fast launches and patrol boats, many of which were built at the specialist boat building facilities at Platt’s Eyot, an island in the Thames near Hampton Court Palace.
Two of the most notable pre-First World War boats shown in Blanche’s notebooks were the motor launches HMS Mimi and HMS Toutou.
Both were built at Chiswick and supplied by Thornycroft to the Royal Navy for ‘The Tanganyika Naval Expedition’. These turned out to be the fastest vessels on Lake Tanganyika, an important and vital necessity during the naval struggle between the British and German forces at the outbreak of World War One. Blanche had worked extensively on the testing of these boats with her father and is thought to have attended their final testing on the Thames, before their departure for Africa.
During World War One, and with Blanche’s involvement, these designs were subsequently developed by J I Thornycroft & Company into the torpedo carrying Coastal Motor Boats (CMBs).  These were used to great effect in raids on Zeebrugge and Ostend during the war and against Bolshevik ships in Kronstadt harbour in 1919.
That same year, Blanche became one of the first three women to be admitted as Associates of the Royal Institution of Naval Architects, alongside engineers Rachel Parsons and Eily Keary.
Sir John passed away at home in 1928, leaving Blanche to carry on his good works whilst her brother John Edward Thornycroft concentrated running on business.
Blanche was very much a ‘backroom boffin’ and continued to managing the now more formal Test Tank facilities at Bembridge. In the very early 1930s, Blanche was involved in trials of what were often referred to as ‘Skimmers’ (racing motor boats). She was also keenly involved with the trials of the fastest ever model to be tested in the tank – that being the model for ‘Miss England III’.
Miss England III
Miss England III
Built by Thornycroft for Sir Henry Seagrave and Kaye Don, Miss England III broke the Water Speed Record at 119.81 mph on 18th July 1932 at Loch Lomond, powered by the same Rolls Royce R engines as used by the Supermarine S6B racing aeroplane. Seagrave himself acknowledged the achievements of the designers during his speech at the celebration party held at Woolston in his honour.
The last recorded date of Blanche being engaged in naval architecture work was in 1935 (at the age of 62), when she was working on a ‘special launch’ for the RAF.
Blanche also involved herself in wider life on the Isle of Wight. Along with her mother she helped found the Bembridge Nursing Association. She also had an active interest in botany and was a council member of the Isle of Wight Natural History and Archaeology Society.
She never married but her recreational interest in sailing, and membership of the local sailing club continued until her death on 30th December 1950.
One thing is for certain, Blanche Thornycroft made a major contribution to marine engineering and hull design, so often thought of as being a ‘mans-world’.
Thankfully, John Thornycroft recognised that same ‘something’ in Blanche that had been seen in him by his father 150 years earlier.

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