Froude, William (1810-1879)

English engineer and hydrodynamicist who first formulated reliable laws for the resistance that water offers to ships and for predicting their stability. He also invented the hydraulic dynameter (1877) for measuring the output of high-power engines. These achievements were fundamental to marine development. Froude was born in Devon and educated at Oxford. He remained for a time at Oxford, working on water resistance and the propulsion of ships. From 1859 he carried out tank-testing experiments at his home, first in Paignton and then in Torquay. In 1838 Froude assisted Isambard Kingdom Brunel on the building of the Bristol and Exeter Railway. Brunel later consulted him on the behaviour of the Great Eastern at sea and, on his recommendation, the ship was fitted with bilge keels. Beginning in 1867, Froude towed models in pairs, balancing one hull shape against the other. Realizing that the frictional resistance and the wave-making resistance follow different laws, he also towed submerged planks with different surface roughness. He was able to establish a formula which would predict the frictional resistance of a hull with accuracy, and formulated Froude's law of comparison. This stated that the wave-making resistance of similar-shaped models varies as the cube of their dimensions if their speeds are as the square root of their dimensions. With these two analytical results, Froude had found a reliable means of estimating the power required to drive a hull at a given speed. Froude also carried out model experiments and theoretical work on the rolling stability of ships. His general deductions are still the standard exposition of the rolling and oscillation of ships.