Necessity is the mother of invention. And it was the necessity of transporting passengers from Europe to America, swiftly and in style, that drove the technological development of these two history-making ships.

Specifications

			Normandie		Queen Mary
	Length		314 metres		311 metres
	Weight		80,552 tonnes		82,070 tonnes
	Power		160,000 horsepower		200,000 horsepower
	Cruise Speed		29 knots		28.5 knots
	Full speed		32.2 knots		32 knots
	Passengers		1972		2139
	Crew		1345		1101

Hull design

Whilst the Queen Mary's traditional hull design copied that of the liners that preceded her, Russian designer Vladimir Yourkevitch blazed a new trail with the French liner Normandie. Imagine looking down on the ship from above – her sides ran parallel for much more of the ship's length than on traditional designs. And whereas traditional hulls narrowed gradually to the bow (front) and stern (rear), the Normandie came in at a sharper angle. To make the ship more stable on the seas, Yourkevitch flattened much of the bottom of the ship. He gave the bow an inward curve to increase its efficiency at cutting through the water, and he curved the stern to reduce the wake. At the base of the bow he included a bulbous projection, the 'forefoot'; this forces a bigger hole in the water through which the vessel can travel – more effective than a sharply pointed bow.

These design differences allowed the Normandie to cruise more efficiently through the water than the Queen Mary, even though the steel ships were of a similar length and weight. Consequently, the Normandie needed less power, therefore smaller engines, to power her. The Normandie needed only 160,000 horsepower compared to 200,000 for the Queen Mary.

Engines

The Queen Mary was a traditional ship all the way down to her engine room. She used steam turbines that, via reduction gears, directly drove the propeller shafts. The reduction gears are necessary because propellers are only efficient when turning at relatively slow speeds. But the turbines must turn faster in order to generate enough power to move such a massive ship. There are three major disadvantages to this method however: the reduction gears are difficult and expensive to make; assembling the turbines, gears and propeller shafts in line is not straightforward; and, as the turbines can only turn in one direction, separate, opposite-direction turbines must be installed to enable the ship to go astern (reverse) when the need arises.

The Normandie design team, mindful of these problems, employed an alternative and relatively new power system for the time. They connected the ship's steam turbines to electrical generators. The power was then fed from the generators to the propeller shafts. Although slightly less efficient and involving somewhat heavier components, this method addressed the three disadvantages of the Queen Mary's engine room and became a popular way of powering large ships.