A dolphin is obviously not a golf ball. However, many scientists believed that the way one slips through the water and the other through the air owed to the same cause: similarities in surface texture and their effect on drag and locomotion.
A groundbreaking new study published July 17 in the Royal Society Biology Letters Journal has upended some of that thinking, demonstrating that in regard to dolphins, at least, it is based on faulty assumptions and measurements. “How smooth is a dolphin? The ridged skin of odontocetes,” co-authored by Professor of Biology George V. Lauder, makes use of an innovative new technique to disprove the earlier supposition.
The reasoning behind the older comparison was sound in terms of fluid dynamics. “Golf balls are dimpled,” said Lauder, who published the research with Dylan K. Wainwright, Ph.D. ’19, Frank E. Fish, Sam Ingersol, Terrie M. Williams, Judy St. Leger, and Alexander J. Smits. “That’s because if you have the right surface roughness, you can reduce the drag tremendously and the ball travels much farther.”
This hypothesis grew out of research published in 1936 in which the British zoologist Sir James Gray posited what became known as “Gray’s paradox,” theorizing that only some special quality of a dolphin’s skin could allow it to swim as fast it did. However, Gray had been able to study only rigid models of the marine mammals, and his findings were based, in part, on “a flawed idea about how muscles generate force in swimming,” said Wainwright, a postdoctoral fellow and first author on the new paper.
Earlier studies of dolphin skin appeared to support Gray’s idea, as most samples exhibited ridges, which were considered key to reducing drag. Many of those samples, however, had been removed from the marine mammals, which had caused the skin to wrinkle. Wainwright, Lauder, and their colleagues knew they would have to look closer at how skin actually functions — by studying it on a living animal.