L is for Loggerhead

L is for Loggerhead

By Joshua Stewart

A few years ago, the Georgia Department of Natural Resources (DNR) approached Georgia Tech civil engineers David Scott and Paul Work with a request.

It was, to say the least, unusual: Could they use structural and materials engineering principles to understand what happens to turtles when they’re struck by boats? At the time, officials were seeing a spike in turtle deaths in the state’s coastal waters, and they wanted to find ways to protect the animals, while balancing recreational and commercial use of the waterways.

Scott and Work were intrigued, so they signed on and set about testing turtle shells, much the same way they might test a sample of steel or concrete. It wasn’t easy — the shells are not the same thickness throughout and they have a natural curvature that makes them difficult to test.

Using the results of these tests, the team built a large number of artificial turtle shells using fiber reinforced polymers. They affixed the shells to artificial turtle bodies, added instruments and sensors, and zoomed over the test specimens with a variety of boats to get a sense of the damage such impacts would cause. They used that data to build a better “shell” with polyurethane foam and a specialized polyester resin and ran another series of tests in the water.

“We found that the engine type and the speed at which you hit [the turtle] are primary factors for determining the lethality of vessel strikes; the depth of the turtle and the hull shape don't have a significant impact,” Scott said. “If a turtle gets hit by a propeller at speed, whether it's at the surface or deeper in the water, it is likely going to have a catastrophic injury.”

Turtles struck by jet-driven watercraft or just the hull of a boat are likely to avoid serious injury and survive, Scott said, which is valuable information for state officials considering whether new restrictions on boaters make sense.

“If you had areas where you were very concerned about catastrophic injuries on turtles — for example, in breeding areas — you may not need to completely restrict boats from those areas, but you could restrict boats with propellers from traveling at speed in those areas,” he said.

Scott said the DNR took the team’s advice, weighed it against the impact of new regulations, and restricted propeller-driven craft in some areas where the turtles liked to nest.

“We didn't provide the final answer to their questions, but we certainly provided them with data that they could use to make decisions,” Scott said.

“What makes this unique was that we weren't trying to build a better turtle, and we weren't trying to take the concepts of what makes a turtle shell work very well and apply them to civil infrastructure,” he said. “We were trying to understand, when turtles come into contact with man, is it always a catastrophic occurrence? And are there ways that we could limit those interactions that would benefit the turtle, while still allowing folks to do the kinds of things that they like to do and still have access to these regions?”

“It was a really unique chance for me to take things that I had been using for a long time as a structural engineer and apply them in a way that I had not previously considered.”

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