Queen Mary's Speed Secrets

Manawatu Times, Volume 61, Issue 43, 21 February 1936, Page 5

Queen Mary's Speed Secrets

Four spare propellers are. to bo kept at Southampton for the uso of the liner Queen Mary w r hen she goes into service. The first of them has just left the foundary at Millwall for the Gunard . stores depot, states a writer in the “Daily Telegraph.” Each weighs 35 tons, is 20ft wide, and has blades of a maximum breadth of over six feet. They are tho largest ever made and, for technical reasons, their size-is not likely to be surpassed. From experts of the Manganese Bronzo, and Brass Company, the makers, I learnt something of the calculated power represented in the four massive blades of each screw. Every minute, as the Queen Mary travels on her . voyages, 6,500,000 gallons of water will bo “expelled” by

each of the four screws. The tips of the blades, whirling through tho water at ;150 miles an hour, will each travel a distance of about 30,000 miles on the round trip. So great is the strain imposed upon the r equipment that the propellershaft in action is twisted round several degrees from the normal. Each, blade yields elastically to the terrific pressure, although at its root the special manganese bronze of its construction is a foot thick. A mild electric current is actually set up between the ship's hull and the churning screws as she travels through the water.

The great liner will be “sucked” rather than “pushed” through tho water. Actually, two-thirds of the propulsive effort is exerted by the back, or suction, face of the blades and only one-third by the so-called driving face. A dozen experts have worked for two years on the design of the propellers—they cannot be mass produced. Weather conditions, speed requirements, clearances, characteristics of each radial section of tho blades—based to some extent on aeronautical principles—and choice of materials, were all factors-to -be considered. Cavitation—the formation of a vacuum on part of the blades at certain speeds of revolution, of cardinal importance to the life of the propellei and the vessel’s- speed—and erosion

had to bo overcome, in relation to the Queen Mary’s specifications.' The final design was the result of many tank experiments, and the study of the efficiency curves of whole 11 families ’ ’ of. other propellers.