Every day more than 1,000 jet airliners cross the Atlantic on scheduled flights. Before the advent of this air bridge, however, the usual way to travel across the sea was via ocean liner. These swift passenger ships vied for the Blue Riband honor, which was accorded to the ship making the fastest average speed while crossing between Europe and North America. The ship that still holds the Blue Riband is SS United States which captured the honor in 1952 driven by the work of a naval engineer named Elaine Kaplan who designed the ship’s four propellers.
Kaplan was an undergraduate mathematics major at Hunter College in Manhattan when she began working for Gibbs & Cox naval architects in New York City. The Second World War was underway and Kaplan with her meticulous math ability was involved in the design of USN battleships and aircraft carriers. After graduation she worked at the naval architecture firm full time and her responsibilities rose quickly due to her excellent skills in designing naval propulsion systems. When Gibbs & Cox was awarded the contract to design the fast new ocean liner that was to became SS United States, Kaplan was tasked with a major role in devising propulsion for the ship.
One of the problems that naval architects must solve with high-speed propellers is the phenomenon of cavitation. As propellor blades move through the water, if they are not designed properly, they can cause pressure differences that lead to the formation of bubbles. These bubbles reduce the efficiency of the propellor, produce harmful vibration and can actually damage the metal prop blades when the bubbles collapse. Since United States was planned as a fast ship with four big props, Kaplan had to design around this issue.
The solution was brilliant in its simplicity. Instead of trying to make all four props the same configuration, she realized that the ship could use four-bladed props for the two outboard propellors and employ five-bladed props for the two closest to the ship’s centerline where the waterflow was more turbulent and bubble formation more likely. Kaplan also worked hard to design the pitch angle of the blades to further reduce cavitation. Kaplan’s efforts allowed United States to secure the Blue Riband honor establishing a record never broken by another liner.