For much of Wednesday, a small group of volunteers and researchers walked in and out of the surf testing a new form of surveillance on the biggest killer of beach swimmers - rip currents.
Again and again the researchers toted 3-foot yellow-and-green contraptions fashioned from foam, plastic sewer pipe, gym weights and cheap GPS units into the surf, then walked along the beach to wherever the odd devices washed up and retrieved them under the gaze of puzzled sunbathers.
Rip currents are blamed for killing 62 beachgoers in North Carolina since 1999. They are thought to be responsible for 80 percent of all U.S. surf rescues and are by far the most common reason that coastal swimmers drown.
"It's really frightening for swimmers, because it's like an endless treadmill for them," said Simon Sanders, the ocean rescue supervisor for Carolina Beach, who was part of the research team Wednesday.
The vast majority of his lifeguards' rescues, he said, were because of rip currents, though the lifeguards, who know how to deal with the currents, often use them to zip out more quickly to swimmers in trouble.
The nature of perilous currents seems straightforward: Water piles up between the beach and an offshore sandbar, then finds a low point in the bar and rushes back out to sea, sometimes carrying hapless swimmers with it.
But scientists have only recently begun figuring out the life-and-death nuances of the currents. The 22 "data-logging drifters" that the team on the beach deployed Wednesday up the center of a weak rip current are thought to be the first ever used on the East Coast.
The team hopes the research will lead to more accurate ways of predicting rip currents and also, perhaps, better methods of escaping them.
The gadgets float along more or less as swimmers would and let researchers precisely and repeatedly track where the rip currents take them. They also gather other data on the currents' behavior, said Spencer Rogers, the coastal erosion and construction specialist from North Carolina Sea Grant who led the construction of the drifters.
Sea Grant, which sponsors research, education and outreach on coastal issues, paid for the drifters and is partnering on the project with the National Weather Service, The Center for Marine Science at UNC Wilmington and several local lifeguard programs.
On Wednesday, the surf was relatively calm and the likelihood of dangerous rip currents was at the lowest of three risk levels that the National Weather Service uses for predictions. The group had set up right in front of a rip current that had been seen in the same location for weeks.
The rip current clearly was happening, with a dark patch of more or less calm water showing where the current split the surf on its way out to sea. The current was weak, though, and several swimmers and surfers bobbed cheerfully right in the middle of it.
The lack of danger actually underlined one reason why the research that could improve forecasting rip currents is important: They are unpredictable.
The currents develop constantly, but a given stretch of beach in North Carolina may develop the right combination of conditions - such as wave size and frequency, tides and sandbar shape - to create lethally strong ones only five to 10 days a year, said Rogers.
"They're almost never dangerous, but when they are, Michael Phelps couldn't keep up with one," he said.
The research also could lead to different advice about how to behave when caught in a rip current.
One of the volunteers Wednesday was something of a celebrity in the world of coastal research - Rob Brander, who was visiting from the University of New South Wales in Sydney, Australia, as part of a multinational research trip.
The formal recommendation for escaping rip currents has long been to swim parallel to the beach until you're out of the relatively narrow band of flowing water. That has been the theme of a national rip current awareness campaign that for more than a decade has been an international model.
But Brander, an expert on surf behavior, said that in recent years researchers using drifters in Australia, the West Coast of the United States and elsewhere had found that in many cases the currents form eddies that will return you to the beach if you simply float along with the flow.
The chances of that working in the currents studied were perhaps 80 percent to 90 percent.
That, Brander said, started a debate among experts about whether to continue telling people to swim parallel to shore or to float and wait.
Of course, the handful of cases that would shoot swimmers straight out and not return them could be fatal for weak swimmers.
Complicating things further, conditions can vary greatly on different kinds of coastline, and no one had really studied rip currents here the same way.
"A lot of people on the East Coast said, 'Ours don't behave that way,' " Brander said.
The new research project aims to find out.
The event Wednesday was partly to practice one last time before beginning the research in earnest. Instead of picking a random day to gather data, researchers will wait for lifeguards and the National Weather Service to alert them when rip current conditions are ripe.
The researchers will mostly gather data near Wilmington this summer, but in August they will make a foray north to the Outer Banks. They want to expand the program to other Atlantic states in the next couple of years, Rogers said.
Meanwhile, Brander said, the advice for beachgoers is pretty simple: If you know how to spot the tell-tale darker water and flatter surf of a rip current and are a good enough swimmer to get out of one, fine. If not, find a spot on a beach near a lifeguard or don't go in the water past your knees.
It's not so much the rip current that kills many of those who drown as it is the panic that getting caught in one triggers, Brander said.
His latest research includes investigating the human side of the danger by polling people who have been caught in rip currents to learn more about the experience and what that might tell researchers about how to improve beach safety.
Rip currents, he said, deserve a higher profile.
"There is this complacency, because they might only kill one or two people at a time," he said. "In Australia, they don't get much attention, but they kill more people than cyclones, bush fires, floods and sharks combined."
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