When we were invited along to the set of Johannes Roberts’ survival thriller 47 Metres Down, a film set in Mexico, it took us by surprise somewhat when we were informed it was in fact Basildon where we’d be spending the day. It does make perfect sense, however, that the shoot takes place in Essex, for it’s the home of the unique Underwater Studio – and it’s here the vast majority of this narrative unfolds, on the bed of the ocean.

The premise is simple – two sisters, played by Mandy Moore and Claire Holt, get trapped in a cage on the sea bed, 47 Metres Down (of course) and with a dwindling supply of oxygen. Naturally you would just assume they could swim upwards and ensure their safety – but there are sharks circling. For Roberts, the man behind The Other Side of the Door and Storage 24 – the appeal to this project is the sheer originality of it.

“What’s interesting for me is that this has never been done before,” he told us during a rare, short-lived break. “It’s an hour and a half long drama under water. And sharks? Everybody loves sharks. But this film isn’t all about sharks, it’s a survival movie that just happens to have sharks in it.”

“It’s a genre movie, I would describe it as a survival thriller, it’s definitely not a shark movie, the sharks are in the background. It’s like Gravity under water. That’s how we’d like to present it, 127 Hours, that kind of thing.”

It was for this very reason this project alerted the formidable Weinsteins to get involved – which Roberts believes adds a good pressure on the project.

“The Weinsteins’ are very actively involved in this and have been in the casting. There’s pressure, but it’s great, and if the movie works as it should do, they have the ability to put it out wide, which is what I want this movie to do.”

What comes with treading over such new territory, is a lack of former guidelines – and for actress Mandy Moore she found this newfound freedom to be somewhat liberating, if daunting.

“One of the appeals of doing this is that it’s never really done before, and with that comes a whole new set of trials and tribulations and obstacles,” she said. There’s no precedent that’s been set necessarily, so I have my fingers crossed it looks as cool as I think it will.”

47 Metres DownSat down, still dying off from her previous scene, Moore spoke of the challenges that derive from shooting a movie under water – which naturally affects your appearance, too.

“I’ve been under water so long I feel like a giant, dehydrated piece of fruit,” she laughed. “As used to you get jumping into the water every day, there are a new set of challenges. The most surprising thing to me is that we’re down there for like an hour at a time. When you’re down there you’re fine, game to try whatever needs to be done, and you feel like you have endless amounts of energy. Then you get to the surface and you feel so drained, you don’t realise how much energy you expend when you’re down there. I’m still surprised by it.”

“At the end of the day Claire and I just sit in the car, and we can’t even say anything to each other we’re so exhausted. But I have slept better these last couple of weeks than I have in a long time, because you’re just so tired. But hey, if I don’t come out of this film with a better lung capacity then I’ve done something wrong.”

The exhausting nature of the project was something that Holt also discussed with us, but she also cites just how much of a learning curve this project represented, which as an actor can only be a good thing.

“It’s exhausting,” she said. “All the experts said at the start that we’d be tired, but I thought – how can we possibly be that tired just sitting in a cage? But it’s really draining. But it’s also so much fun, really different to anything I’ve done before.”

“It’s been such a huge learning experience. You have your methods and techniques, but obviously coupled with the fact our face is covered by a mask, and the communication is different and it’s difficult to hear. It’s definitely something we’ve struggled through, but we’re getting some amazing stuff.”

What did prove to be less of a challenge for the two actresses, however, was acting scared. When genuinely in a water tank, and genuinely using oxygen machines – to get into the headspace of the character came quite naturally.

“It’s not easy to lose that sense of foreboding fear, the anxiety is always there,” Holt continued. “Especially during the first part of the shoot when we weren’t used to the equipment. Being under water for that length of time is nerve-wracking and you have to trust the people around you. But in terms of the drama and tension of the film, it’s not hard to portray.”

47 Metres DownSuch sentiments were echoed by Moore. “The sharks are scary, for sure, but the prospect of being trapped at the bottom of the ocean, running out of air, that’s what really resonated with me when I read the script initially, that’s what made my heart feel like it was in my throat. Drowning, and running out of oxygen is way scarier than a shark. I keep reminding myself of that and it’s easy to be scared.”

For Roberts, coming at this from a more technical viewpoint, it was the task of capturing the nuance and subtlety to the actresses’ performances which proved to be a challenge, particularly when the majority of their face was covered by a diving mask.

“The masks are custom made so you can see the whole face. Both girls have such expressive faces and it’s all in the eyes, and they have amazing eyes. When you’re struck in that situation under water, it’s so intense that it just comes across anyhow,” he said.

He did admit he had to warn both Holt and Moore, that while an rewarding experience, it most certainly wouldn’t be an easy one.

“We said to them, look, this is a pretty intense film, will you be okay with that? And you hear that it’s going to be fine, but it’s only when you actually get down to it, that you have to see if they can sink or swim – but they’ve just been amazing. It’s been very tough for them, though.”

But for the two lead women the core of this narrative, and what drives it from an emotional viewpoint, is the study of human condition, and one of the aspects that they could resonate with is the sibling relationship – and for Holt, she was just thrilled that it was Moore who was cast alongside her.

“We have formed a close relationship, it’s just the two of us and we have to rely on each other, for a lot of things, not just in the scene but outside of it as well,” she said. “I’m so grateful to have been cast alongside her, because she’s a true teammate and really generous, and also wonderful to work with, it’s been really nice and I feel very lucky.”

47 Metres Down is released on July 26th.