Repellent Coating Developed to Reduce Friction Drag on Navy Vessels, Reduce Fuel Costs

The Navy has sponsored work by researchers at the University of Michigan to develop a rubber-like coating that could make ships and other vessels more resistant to drag.

In work sponsored by the Office of Naval Research (ONR), Anish Tuteja, an associate professor of materials science and engineering at the University of Michigan, developed what’s called an omniphobic coating that can repel a number of substances—including water, oil, alcohol, and even peanut butter.

Low friction coating may serve Navy
Mathew Boban, a graduate student research assistant at the University of Michigan, pours hexadecane oil onto a glass slide covered with an omniphobic coating. The Office of Naval Research is sponsoring efforts to see how omniphobic coatings might reduce friction drag—resistance created by the movement of a hull through water—on ships, submarines, and unmanned underwater vessels. (Image source: Robert Coelius, Michigan Engineering Communications and Marketing) 

Better Efficiency

The Navy thinks it can save significantly in fuel costs by using the coating to reduce the amount of energy that vessels consume and improve overall efficiency.

“A significant percentage of a ship’s fuel consumption goes toward maintaining its speed and overcoming friction drag,” said Dr. Ki-Han Kim, a program officer in ONR’s Sea Warfare and Weapons Department in an ONR release. “If we could find a way to drastically reduce friction drag, vessels would consume less fuel or battery power, and enjoy a greater range of operations,” he further stated in the release. Indeed, ships use up to 80 percent of their fuel at lower speeds and 40 to 50 percent of fuel at higher speeds for this function, he said.

Friction drag occurs when resistance is created by the movement of the hull of a ship, submarine, or unmanned underwater vessels through water. It’s similar to the same resistance humans feel when trying to move through water, such as by walking in the ocean or a swimming pool. Each stride requires more energy and effort.

Coatings

Developing a coating to repel the range of liquids needed to significantly reduce the drag of ocean vessels was not an easy task, however, because the science necessary is very complex.

“Researchers may take a very durable polymer matrix and a very repellent filler and mix them,” he explained in the release. “But this doesn’t necessarily yield a durable, repellent coating. Different polymers and fillers have different miscibilities [the ability of two substances to mix together]. Simply combining the most durable individual constituents doesn't yield the most durable composite coating,” he added.

Tuteja and his team developed the omniphobic coating after doing extensive research of known chemical substances. They then used complex mathematic equations based on each substance’s molecular properties to predict how any two would behave when blended. Only after studying and analyzing hundreds of combinations did they believe they found an appropriate mix for what they wanted to achieve.

The rubber-like coating can be sprayed, brushed, dipped, or spin-coated onto numerous surfaces, where it will bind tightly. It is very durable, able to withstand scratching, denting, and other hazards of daily use, researchers said. Moreover, it is optically clear, thanks to the way the molecules separate, they said.

Researchers posted a video on YouTube that demonstrates a test of the coating. Tuteja said that in addition to its intended use, the Navy also could use the coating to protect high-value equipment like sensors, radars, and antennas from weather.

The University of Michigan team is conducting further tests on the omniphobic coating and plans to have it ready for small-scale military and civilian use within the next couple of years.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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