A Treatise On The Principles And Practice Of Dock Engineering

514 DOCK ENGINEERING. Crane Tests.—Tests with cranes afford a convenient and the most practicable criterion of power expenditure,* and some very interesting experiments have been made in this connection by M. Delachanal, the engineer to the Havre Chamber of Commerce, the results of which are tabulated below. The operations, which were carried out at the port of Havre, consisted in the lifting of loads of 29'5 cwts. (1,500 kilogrammes) and 7’88 cwts. (400 kilogrammes), respectively, by each crane to a height of 29'5 feet (9 metres), at which point the crane was slewed through an angle of 180° and the load lowered and deposited. The empty hook was then raised to the same height, steered through a semicircle in the inverse direction, and lowered for a fresh load. In the case of electrical power, variation in speed was effected by a rheostat in series with the motor. The actual working expenditure per hour is given by multiplying the tabular figures by 30, 40, or 50, according to the rate of working. TABLE XXXVIII.—Expenditure of Energy by Cranes in Foot-lbs. per Operation. Speed in Feet per Sec. Duration of Lift in Secs. Hydraulic Crane. Load. Steam Crane. Load. Electric Crane. Load. 29’5 Cwts. 7'88 Cwts. 29’5 Cwts. 7'88 Cwts. 29°5 Cwts. 7-88 Cwts. •492 60 318,975 190,589 458,543 359,263 913,332 564,600 1 312 22-5 318,975 190,589 496,053 380,860 411,868 295,656 278,998 2-132 13-85 318,975 190,589 566,054 392,525 212,049 The work effectively performed in each case was 97,645 ft.-lbs. and 26,038 ft.-lbs. respectively. The figures demonstrate the disadvantage of making steam cranes work too quickly and electric cranes (with series wound motors) too slowly. At the higher and more usual speeds, steam cranes are shown to be niuch inferior to hydraulic and electric cranes. Equally interesting experiments have been restricted to a comparison of these last two agencies. Thus, Mr. Philip Dawson f has recorded the following expenditure of power in watt-hours for hydraulic and electric cranes under similar conditions of working. The cycle of operations consisted of a lift of 36'1 feet, a slew of 140°, and a lower of 13 feet, all under load, with the inverse movements unloaded. The hydraulic crane had three powers. * It is diffieult in the case of other apparatus to obtain identical conditions for the purpose of experiment. + Traction and Transmission, May, 1903.