Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 142,834 pages of information and 228,772 images on early companies, their products and the people who designed and built them.
Blanche Coules Thornycroft (1873-1950), marine engineer, Associate of the Institution of Naval Architects
1873 December 21st. Born in Kensington the daughter of John Isaac Thornycroft and his wife Blanche Ada, née Coules (1846–1936).
1891 Blanche C. Thornycroft (age 17 born London), living at Steyne House, Brading, Hants with her father (age 48 born Rome), a Civil Engineer and employer and mother, Blanche A. (age 45 born Gloucester), and siblings Edith A. (age 19 born London), Mary B. (age 15 born London), Ada F. (age 13 born London), Eldred E. A. (age 12 born London) and Isaac T. (age 9 born London). Also a visitor from Brazil and five servants. 
1911 Living at Eyot Villa, The Mall, Chiswick: John Isaac Thornycroft (age 68 born Holy Rome), Marine Engineer (Retired). With his wife Blanche Ada Thornycroft (age 64 born Gloucester) and their three children; Edith Couish (age 39 born Hammersmith), a widow; Blanche Coules Thornycroft (age 37 born Hammersmith); and Eldred E. A. Thornycroft (age 32 born Chiswick. Also his mother-in-law Elizabeth Coyles (age 94 born Hants). Six servants. They have been married 41 years and have seven children.
By 1919 she had been in complete control of the Steyne Experimental Tank, and had carried out experiments on various type of vessel, particularly high-speed skimmers. Elected an Associate of the Institution of Naval Architects.
1938 She continued testing model hulls for the company for some ten years after her father’s death in 1928.
She was a member of the Women's Engineering Society.
1950 December 30th. Died, of the Moorings, Bembridge, IOW. Spinster.
1951 Obituary 
The death occurred suddenly on Saturday afternoon at her home, The Moorings. Bembridge, of Miss Blanche Coules Thornycroft, aged 76. She was the second daughter of Sir John I. Thornycroft, the naval architect, and founder of the shipbuilding firm, and sister of Sir John E. Thornycroft and Mr. Tom Thornycroft, the wellknown small boat sailor.
Miss Thornycroft's association with her father's work as a ship designer was more intimate than is generally known. At Steyne, the family seat at Bembridge, the late Sir John Thornycroft had specially built a large testing lank for his ship models. It was Miss Thornycroft's duty to keep and work out the records obtained at these tests, and she thus had an early knowledge of many outstanding naval and power racing craft which the firm subsequently produced.
With her mother, the late Lady Thornycroft, she helped found Bembridge District Nursing Association about 50 years ago. and she was one of the oldest women members of Bembridge Sailing Club.
Cremation takes place tomorrow, and a memorial service will be held at Holy Trinity Church, Bembridge, at 2.30p.m. the same day.