“It’s so graphic. But I couldn’t quite get my body to throw up,” she says.

“When you’re seasick and finally able to throw up, you kind of get your footing again.

“I wasn’t able to do that. It was just an all-day nausea and quite miserable.

“I just prayed the rest of the shoot wouldn’t be like that, knowing we had months on the sea to go.”

Woodley was buoyed by the fact that she, co-star Sam Claflin and the small crew, who also suffered though first-day seasickness (“It’s the best icebreaker!” Claflin, 31, says), found the sea legs to shoot for five weeks on the open ocean.

Adrift (released in cinemas around the world from Thursday) is the real-life adventure story of Tami Oldham (Woodley), who survived 41 days stranded at sea in 1983.

Newly engaged, Oldham and Richard Sharp (Claflin) were sailing on the romantic trip of a lifetime from Tahiti to San Diego when they were struck by a devastating hurricane.

The film’s cast and crew were all smiles heading out that first day on what seemed like a dream job. Two hours later, a storm picked up, and smiles were replaced by pale looks.

“And the stench of vomit started creeping up on deck,” Claflin says.

“Pretty much everybody threw up at least once.”

A tough start, but Woodley notes it was “good preparation, immediately putting us on our toes, knowing what kind of resiliency we needed to harness”.

Director Baltasar Kormákur even used the actors’ queasy looks to convey worry about the approaching hurricane.

“What the audience sees in that scene is a look of nervousness,” says Woodley, laughing.

“But it’s really Sam and I trying not puke when the cameras are rolling. It’s like, ‘Keep it together’. That’s pure anxiety.”

Woodley and Claflin set out on the open ocean for 15-hour days off Fiji. (Hurricane scenes were shot on a set using digital effects for the storm.)

Along with the innumerable filmmaking challenges of shooting on the water, the cast and crew had to deal with everything from no mobile phone signal to a shooting schedule largely dictated by the weather.

“And when you’re stuck on a boat with 15 people every single day, you’re all dealing with things like the toilets breaking and everyone just having to jump in the ocean to use the bathroom,” Woodley says.

“There’s a lot of discomfort, there’s a lot of bodily smells. And a lot of humour. That’s the glue that keeps everyone together.”

Woodley undertook a strict diet to reflect Oldham’s ordeal with dwindling food, typically eating a breakfast of two egg yolks with steamed broccoli, a similar lunch and no dinner.

In a scene where Woodley feeds herself and her wounded fiancé newly discovered peanut butter with her fingers, there is true joy captured in the actors’ eyes.

“We were both so bloody hungry,” Woodley says. “The fact that we got to eat just pure salty fat in the form of peanut butter was heaven on Earth It made that scene very authentic.”

She makes clear that those challenges took place in a vastly different world from the heroic tale told on-screen, which Oldham wrote about in her 1998 book Red Sky in Mourning: A True Story of Love, Loss and Survival at Sea.

Even a scene where Woodley meditates naked on deck shows Oldham’s dramatic plight and mindset.

“If you’re stripped down to your core – mentally, physically, psychologically – it makes sense you would chose to meditate naked. Just to sort of surrender everything to Mother Nature,” Woodley says. “It’s not about exploitation. There isn’t a love scene in this movie. Clothes were not that important alone out at sea.”

Woodley is fully restored to land life, sporting the dark fringe needed to play Jane Chapman in the second season of HBO’s Emmy Award-winning Big Little Lies, which is filming now.

She’s in awe of the screen achievement and the daily, stunning nature moments captured for Adrift, which made the emotional toil worthwhile.

“When you see the sunrise and sunset from the middle of the ocean every day, no matter [what] you’re doing, life is put in perspective,” Woodley says. “And you just feel lucky to be there.”

Want more stories like this? Sign up here. Follow STYLE on Facebook, Instagram and Twitter