- Froude, William (1810–1879)
- Engineering & Materials
- Froude, William (1810–1879)
Froude, William (1810–1879)
English engineer and hydrodynamiscist who first formulated reliable laws for the resistance that water offers to ships and for predicting their stability. He also invented the hydraulic dynameter for measuring the output of high-power engines. These achievements were fundamental to marine development.
Froude was educated at Buckfastleigh, Westminster School, and Oriel College, Oxford, where he obtained a first in mathematics and a third in classics in 1832. He remained at Oxford working on water resistance and the propulsion of ships and in 1838 became an assistant to Isambard Kingdom Brunel on the building of the Bristol and Exeter Railway.
In 1839 he married Katherine Holdsworth of Widdicombe. He probably worked on the South Devon Railway and was intimately connected with the ill-fated atmospheric railroad. In 1846 he went to live with his father at Dartington Parsonage and began work in earnest on marine hydrodynamics. Brunel consulted him on the behavior of the Great Eastern at sea and, on his recommendation, the ship was fitted with bilge keels.
When his father died in 1859 Froude moved to Paignton where he began his tank-testing experiments. His first test-tank was built, at his home, in 1862–3. In 1863 he started to build his own house, known as Chelston Cross, at Cockington, Torquay, and helped the local water authority with its supply problems. In 1867 he began his experiments with towed models. After grudging financial assistance from the Admiralty, he built another experimental tank near his home in 1872.
He described his hydraulic dynameter in a paper to the Institution of Mechanical Engineers in 1877, but did not live to see his machine work. It was built in 1878, the year in which Froude's wife died and in which he became seriously ill. He went on a voyage of recuperation to South Africa but caught dysentry and died on May 6, 1879 in Simonstown, where he was buried.
Froude was elected a fellow of the Royal Society in 1870 and his work was continued by his sons Richard and Robert. Robert built the towing tank for the Admiralty at Haslar, near Portsmouth, and Richard joined Hammersley Heenan to manufacture the dynamometer commercially.
Generally there are two modes in which vessels can travel: by displacement, in which they force their way through the water, and by planing, or skating on top of the water. In the displacement mode, the propulsive power is absorbed in making waves and in overcoming the friction of the hull against the water.
Froude's first successful experiments started in 1867 when he towed models in pairs, balancing one hull shape against the other. Initially he incorporated his findings into a single law, now known as Froude's law of comparison. This states that the entire resistance of similar-shaped models varies as the cube of their dimensions if their speeds are as the square root of their dimensions.
As Froude himself realized, this law becomes increasingly unreliable as the difference in size between the models increases. This is because the frictional resistance and the wavemaking resistance follow different laws. His law of comparisons is now only applied to the wavemaking component.
To estimate frictional resistance, Froude carried out tests in his tank at Torquay, where he towed submerged (to eliminate wavemaking resistance) planks with different surface roughness. He was able to establish a formula that would predict the frictional resistance of a hull with accuracy.
With these two analytical results, using only models and mathematics, Froude had found a reliable means of estimating the power required to drive a hull at a given speed. Model-testing had been tried before but was considered unreliable because previous workers had failed to appreciate that the two major components of ship resistance varied differently. Opponents of model testing maintained that the only way to gather the required information was to work on full-sized hulls. It was this antimodel lobby that was largely responsible for Froude's difficulties in persuading the Admiralty to part with £2,000 for building the Torquay tank.
Froude had done a large amount of theoretical work on the rolling stability of ships and when the Torquay tank was built, he was able to carry out model experiments, relating them to observations made on actual ships. His general deductions were challenged at the time but they were found to be correct and to this day are the standard exposition of the rolling and oscillation of ships.
Engine builders usually need to test their machinery before installation. The friction brake is useful only for lower-power applications, so Froude employed hydrodynamic principles to absorb 1,500 kW/2,000 hp at 90 rpm. His brake consisted of a rotor and stator, both of which were shaped in a series of semicircular cups angled at 45° but of opposite pitch. The change of momentum when water passes from rotor to stator and back again creates a braking reaction. By measuring this braking reaction and the shaft speed, the power of the engine could be calculated.
Froude was a tireless experimenter who put one of the most powerful analytical tools into the hands of marine architects. He has been credited as the founder of ship hydrodynamics. If any one person can be said to have founded anything in engineering, this is probably accurate.
From the Hutchinson Dictionary of Scientific Biography, © RM, 2020. All rights reserved. Published under license in AccessScience, © McGraw-Hill Education, 2000–2020. Helicon Publishing is a division of RM.