The transfer of Ericsson to America left an open field for Mr. Pettit Smith, and the experiments carried out by the Screw Propeller Company had the effect of permanently directing the attention in Great Britain of those interested in such subjects. The screw used in the Archimedes “consisted of two half-threads, of an 8 feet pitch, 5 feet 9 inches in diameter. Each was 4 feet in length, and they were placed diametrically opposite each other at an angle of about 45 degrees on the propeller-shaft” (Lindsay). She was tried in 1839, and in 1840 Mr. Brunel spent some time in investigating her performance. His mind, bold and original in all its own conceptions, was quick to appreciate the new method; and, although the engines of the Great Britain were already begun, designed for paddle-wheels, he brought the directors of the company, who had undertaken the building of their own machinery, to consent to a change. The following details of the ship are taken from the “Life of Brunel:” Total length, 322 ft.; length of keel, 289 ft.; beam, 51 ft.; depth, 32 ft. 6 in.; draught of water, 16 ft.; tonnage measurement, 3,443 tons; displacement, 2,984 tons; number of cylinders, 4; diameter of cylinder, 88 in.; length of stroke, 6 ft.; weight of engines, 340 tons; weight of boilers, 200 tons; weight of water in boilers, 200 tons; weight of screw-shaft, 38 tons; diameter of screw, 15 ft. 6 in.; pitch of screw, 25 ft.; weight of screw, 4 tons; diameter of main drum, 18 ft.; diameter of screw-shaft drum, 6 ft.; weight of coal, 1,200 tons.
“In the construction of the Great Britain, the same care which had been spent in securing longitudinal strength in the wooden hull of the Great Western was now given to the suitable distribution of the metal.”
A balanced rudder and bilge keels were parts of her original construction, and an unusual method of lapping the plates was used. “Apart from their size, the design of the engines of the Great Britain necessarily presented many peculiarities. The boilers, which were 6 in number, were placed touching each other, so as to form one large boiler about 33 feet square, divided by one transverse and two longitudinal partitions.
“It would seem that the boiler was worked with a pressure of about 8 pounds on the square inch.