Gertrude Ederle and the grueling science of marathon swimming

Before you watch the new biopic 'Young Woman and the Sea' about 'Trudy's' record-breaking swim across the English Channel, learn what it takes.
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a black and white photograph of swimmer gertrude ederle. she is standing on a beach in a one piece swimsuit holding an oar.
Gertrude “Trudy” Ederle was the first woman to swim across the English Channel. During a time when female athletes were not taken seriously, she proved critics wrong. National Portrait Gallery, Smithsonian Institution

For two weeks in 1926, a woman held the world speed record for swimming across the English Channel. On August 6, American Gertrude “Trudy” Ederle swam from France to England in 14 hours 31 minutes, beating the men’s record by 1 hour 59 minutes. A November 1926, article in Popular Science described her as a “broad-shouldered and stout-hearted American girl” with a “reason to smile” for her daring Channel crossing. 

Roughly 21 miles across as its most narrow point, this body of water between England and France remains the ultimate athletic test. More people have scaled Mount Everest than have swam across the English Channel in the almost 150 years since the first successful crossing by Matthew Webb.

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Despite being the first woman honored with a ticker tape parade in New York City, Trudy’s story has been generally lost to history. Today, a feature-length film about her epic crossing hits the big screen. Young Woman and the Sea is an adaptation of Glenn Stout’s 2009 book Young Woman and the Sea: How Trudy Ederle Conquered the English Channel and Inspired the World. British actor Daisy Ridley is in the starring role, capturing Trudy’s well-documented tenacity and youthful energy. 

While the film plays fast and loose with some biographical and chronological details, it chronicles her unlikely rise from the measles-stricken daughter of German immigrants to swimming superstar. Importantly, it showcases the barriers, injustices, grit, and the fun experienced by women swimmers in the early 20th century the same way 1992’s A League of Their Own did for the players of the All-American Girls Professional Baseball League. However, where the film shines is highlighting the science and technological advancements available to swimmers almost a century ago. It took–and still takes–a lot of science to get a swimmer across the English Channel.

actress daisy ridely portraying swimmer gertrude ederle.
Daisy Ridley as Trudy Ederle in Disney’s live-action YOUNG WOMAN AND THE SEA. Photo courtesy of Disney. CREDIT: © 2024 Disney Enterprises Inc. All Rights Reserved.

A current that ‘holds you like the hand of God’

Despite looking like a tantalizingly short swim from the stony shores of England or France, the roughly 21-mile crossing is daunting. 

“It’s such a fast running current. You’ve got the North Sea going one way and then you’ve got the Atlantic coming up from the southwest the other way,”boat captain Stuart Gleeson tells Popular Science.  “It’s a lot of variables in that short distance.”

Gleeson captains the Sea Leopard and hails from a fishing family who has been taking charters, film crews, and swimmers across the Channel since the 1920s. Even navigators like Gleeson with 15 years of experience must be on their toes at all times with so many changes in the picture before a swimmer even touches the water. Swimmers are typically given a three week window of possibility during the swimming season from roughly July to September. It’s the boat pilot’s job to make that call, but nature is ultimately in charge.

[Related: Humans are altering Earth’s tides, and not just through climate change.]

“We’re looking at the forecast every 12 hours and every six hours, mainly looking at winds and tide,” says Gleeson. “Obviously, we set off in the best 24 hour weather period that we can, but some swimmers take longer and then you are stuck with the weather a little bit.”

In order to make it across, swimmers generally have about six hours in one direction and six in the other direction. The wind can change directions without much warning and may hold up a tide or push it one way the next day. There are also unexpected storms and shifty winds. These gusts can force an athlete to swim “wind against sea.” This is likened to swimming on a treadmill or completely in place due to the strength of the tide pushing against the ever-changing winds. 

A typical English Channel crossing is in the shape of the letter “S” to take advantage of these tricky tides and currents. Along the way, the pilot is not only navigating the weather and water, but the busy shipping lanes. The English Channel is one of the busiest shipping routes in the world. It’s full of monstrous tankers, passenger ferries, and more that swimmers must be kept a safe distance from. 

In Trudy’s day, the boats were primarily open, meaning the crew, press, coaches, and anyone on board were exposed to the elements. They also did not have the radar technology that Gleeson and other pilots benefit from.

“They had a compass, they left from the beach, and set a course on a compass as much as they could,” says Gleeson. “We found some archive footage in the newspaper archives from around that time that showed fog was quite a big thing.”

The film chronicles just how difficult it could be to get only a few miles offshore and be stuck in place in a “current that holds you like the hand of God.” While the exact number of swimmers who have died trying to cross the English Channel is not known, it’s estimated that 10 to 16 have died since 1926. 

The water is ultimately the great equalizer, but it’s the rush of joy from a successful swim that reaches back to the boat.

“It can be a millionaire CEO of a massive company or it can be your local binman or something you know, but they’ve done exactly the same training,” says Gleeson. “I get passion from seeing everyone that lands on that French beach.”

Becoming a Channel swimmer

One of the few things a swimmer can control before any open-water swim is their preparation. For Trudy, that included years of swimming along the beaches of Highlands, New Jersey with her family, and pool training with the Women’s Swimming Association. She also faced the extreme low of a disappointing run at the 1924 Olympics in Paris. She quickly countered that with a successful 22-mile swim from Lower Manhattan to the tip of Sandy Hook in New Jersey, seen as an American-equivalent to the English Channel at the time. She made her first attempt at crossing the English Channel in 1925 and was potentially sabotaged with tainted tea during the swim. Her success did not come overnight for Trudy, nor does it for most athletes. 

Hypothermia from bone chilling cold water, no assistance from a wetsuit, dense fog, jellyfish stings, seasickness are just a few of the joys that await anyone brave enough to attempt to swim across the English Channel.

While technology, nutrition, and training in the century since Trudy’s swim, the basic fundamentals remain the same. One of the most important steps is to prepare for the cold. The water temperatures range from about 57 to 64 degrees Fahrenheit, ripe for hypothermia if a swimmer isn’t careful. For modern Channel swimmers like sisters Margaret and Vera Rivard, the cold is often the first hurdle.

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“Your body’s initial reaction is to panic,” Margaret, 17, excitedly tells Popular Science. “In the fall and spring, we would go in the water and see how our bodies reacted. It’s kind of just knowing, ‘Okay, I’m cold, but I’m not dangerously cold.’ It’s just getting in and being okay with the uncomfortable.”

“It’s definitely like a mental state that you have to learn how to handle as you swim,” says Vera, 20.

The only way to get through that mental state is to keep safely swimming in cold water, building up a tolerance and a layer of brown fat. This smooth and spongy layer of adipose tissues lies towards the surface layer of skin, similar to a seal or marine mammal. Some swimmers will help this along by taking cold showers or wearing a vest instead of a coat during the colder months. The Rivards use the chilly lakes of Vermont and New Hampshire to train year-round.

vera (left) and margaret rivard stand in the water during a training swim
Vera (left) and Margaret Rivard during a training swim. CREDIT: Darcie Rivard.

This cold training coincides with ratcheting up distances. Channel swimmers can easily log 5,000 to 10,000 meters or yards per training session in the pool with hours-long swims in the open water when possible. To even qualify, swimmers must complete what Americans call a “six hour sub 60”–a documented six hour swim in water that is below 60 degrees Fahrenheit. This must be completed under the rules of marathon swimming. Participants cannot wear wetsuits, but can use a pungent concoction of lanolin often called channel grease. It helps reduce friction and some say it helps retain body heat. Swimmers can wear a maximum of two swim caps, a pair of goggles, and cannot have any physical contact with the boat or crewmembers until they have cleared the water.

As for food, swimmers must also experiment with what they can eat in the water that will also sustain energy. Called “feeds,” anything swimmers will eat are drink are stored on a boat or kayak depending on the swim. A coach or crew member gets feeds to the swimmer by tossing the feed out in a bottle or container tethered to a rope or with a net attached to a pole. Importantly, they cannot touch the swimmer during a feed.

Most swimmers take in some sort of nutrition about every 30 minutes, but that will vary depending on the individual. So will the feeds. They can range from solid foods like peanut butter sandwiches and Trudy’s infamous chicken legs to candy or purely liquid carbohydrates.

“I’ve used chocolate rice pudding. I really like pudding in general,” laughs Vera.

And that proof is in the pudding. Vera successfully swam across the English Channel on September 1, 2020 in 14 hours and 10 minutes. Margaret followed suit on September 6, 2023, in 13 hours and 37 minutes. 

“I know for me, she’s like the best training buddy I could ask for. We push each other to do our best,” says Vera. 

“And we’re also really competitive,” laughs Margaret.

Lillian Cannon, of Baltimore, Maryland, offering her best wishes to Gertrude Ederle, as she starts out from Cape Griz Nez, France, on her successful attempt to swim the English Channel, 1926.
Lillian Cannon, of Baltimore, Maryland, offering her best wishes to Gertrude Ederle, as she starts out from Cape Griz Nez, France, on her successful attempt to swim the English Channel, 1926. CREDIT: Library of Congress Prints & Photographs Division, Washington, D.C.

Both girls did elementary school projects on Trudy, and count her as an inspiration for their own Channel swims. In some ways, their story mirrors Trudy’s, as her older sister Margaret “Meg” was also a swimmer who was on the boat during her successful swim. The pair even fashioned a two-piece swimsuit out of silk about 20 years before the bikini’s official patent to save her skin  from some painful chafing. 

“She was a huge inspiration to us as kids and she was one of the reasons I wanted to do the English Channel personally,” says Vera.

Turning a Jedi into a swimmer

With her starring role in the Star Wars franchise, Ridley was no stranger to physical training for a movie. After all, she had to wield a lightsaber and fight the Dark Side. But that was on dry land. Swimming is a whole other story. 

To prepare, Olympic silver medalist Siobhan-Marie O’Connor was brought on board to help train Ridley. The pair had a few months of pool training in London before the shoot in Bulgaria began. They focused on proper swimming technique before moving on to the fitness and endurance needed to make Ridley look like a marathon swimmer and help her sustain longer bouts in the water for filming. She swam an average of 2,000 to 2,500 meters per workout.

Daisy Ridley during production of YOUNG WOMAN AND THE SEA. Photo courtesy of Joachim Rønning. © 2024 Disney Enterprises, Inc. All Rights Reserved.
Daisy Ridley during production of YOUNG WOMAN AND THE SEA. Photo courtesy of Joachim Rønning. © 2024 Disney Enterprises, Inc. All Rights Reserved. Disney

“In our first session, we had a warm-up of less than a couple of lengths. I remember Daisy found that instantly as a challenge,” O’Connor tells Popular Science. “Fast forward to the end of the shoot and she was swimming incredibly impressive distances in the Black Sea in Bulgaria.”

One of the challenges for O’Connor was how to alter swimming techniques for the pool versus the open water. In the confines of the chlorine box, swimmers can get by with longer strokes. Out in the open water, strokes tend to be a bit shorter and adaptable for changing wind and wave conditions. The hands must also hit the water harder to help keep the pressure off of the shoulders for so many hours of repetitive motion. 

[Related: Why endurance athletes hit the wall.]

O’Connor also studied archival footage of the time to help make Ridley’s swimming look as accurate for the time as possible. One of Trudy’s strengths was mastering the American crawl–what we now call freestyle. The dives and starts were also different and the lightning fast flip turns that Olympicans make were also nonexistent. 

Ridley also had to do some swimming without a very low-tech but important piece of swimming equipment–goggles.

“Initially, we started our training with goggles. But in the competitions of that era most didn’t wear goggles,” says O’Connor. “Daisy had to get used to swimming without goggles for at least a few laps every session.” 

The film even shows how Trudy–who did use goggles for her English Channel swim–and her sister experimented to keep her custom amber colored goggles from leaking with candle wax for a stronger seal.

‘What for?’

All of this preparation, from risking hypothermia, experimenting with nutrition and textiles, and learning how to navigate tides both in the real world and in a movie pays off. This lesson in goal preparation and resilience is easily something that swimmers and non-swimmers alike can take away from the film and Trudy’s life. 

Parade for Gertrude Ederle coming up Broadway, New York City, with large crowd watching, 1926.
Parade for Gertrude Ederle coming up Broadway, New York City, with large crowd watching, 1926. CREDIT: Library of Congress Prints & Photographs Division, Washington, D.C.

“Trudy’s greatest achievement came after such a huge setback. The Olympics was a huge part of her story, but she did something far greater,” says O’Connor. “She was such a trailblazer for women’s swimming and women’s sport in general.”

When her crew and family attempted to take her out of the water at one point during her swim because the swells were hurting her progress in the water, she declined to stop and responded with “What for?” Trudy just kept swimming, changing history as she stood up on that English beach. 

Young Woman and the Sea opens in select theaters on May 31.