I have not seen the movie 47 Meters Down. And unless it comes on television late some night when I’m firing up the vaporizer, chances are I never will.
I have, however, seen the ads for the film. And that alone drove me to chime in here.
The premise of the film is that two women are trapped in a shark cage at a depth of 47 meters. They appear to be wearing standard scuba gear – a single tank of compressed air – which the trailer claims will give them an hour of breathable air underwater. So the decision they have to make, presumably, is whether to try to swim to the surface through shark-infested waters or stay in the cage and hope for some sort of rescue before their air supply runs out.
The problem with this premise is that, at the depth of 47 meters, which is approximately 154 feet, you would be dead long before the hour mark. In fact, on a standard single tank of compressed air, you don’t really have any time to spend at that depth.
I know this for a fact, because I used similar equipment to dive to a depth of 45 meters, or 149 feet. I was diving in the legendary Blue Hole, off the coast of Belize. When I reached that depth, I literally had to turn around and start making my way slowly back up to the surface to 1) ensure that I made it to the surface before I ran out of air and 2) give my body sufficient time (at decreasing depths) to expel the nitrogen that gets absorbed into your bloodstream at such depths.
I am not going to go into the science of why those two things occur, but they are among the first things you learn when diving. And since both of the actresses in this film apparently had to learn how to dive to make the film, and presumably were surround by professional safety divers throughout filming, it’s hard to believe that no one mentioned this to the director. In a word, the premise of the film is ridiculous.
The deeper you go, the faster you consume your air. At that depth, you might have 15-20 minutes of air. And that’s the best-case scenario (for a super-fit, experienced diver). You have to figure that these ladies used up some of their air when they first entered the cage, especially being giddy with excitement, surrounded by sharks. And then when the cage became untethered and dropped 150 feet to the bottom – which, from my experience free falling that depth in the Blue Hole, takes a lot more time than you might imagine (you are falling through water, not air) – they would have used up their air supply even faster, as they began to panic.
Assuming that they somehow did have enough air to contemplate their fate once they finally reached the ocean bottom (in this case, at a depth of 47 meters), which is a really big if considering all the aforementioned factors, then they would only have one option, which is to immediately start their slow ascent to the surface through shark-infested waters. Even if they had enough air to spend a full hour down there (which, again, they would not), the prospect of being rescued in time would still be slim. It’s not like calling an ambulance. The Coast Guard would need time to travel out to the boat, assess the situation, develop a plan of action, and then execute it. And even though Coast Guard rescue divers are among the best in the business, these depths would test even their abilities and limits.
So, ascending through shark-infested waters it is. Now let’s look at Hollywood’s treatment of sharks for a moment. Even in chummed waters, sharks aren’t sitting around waiting for human meatsicles to pop out of the cage so they can tear them to shreds. They are looking for food, but they tend to be rather cautious – especially when humans are involved. And they don’t appear to be very fond of divers. In fact, when I went shark cage diving with Great Whites off the coast of South Africa, we weren’t allowed to wear scuba gear because the noise and bubbles apparently scare off the sharks.
47 Meters Up
From that depth, these ladies would need to gradually make their way to the surface. They cannot shoot straight up like a balloon, or they’d risk getting decompression sickness – the bends. My understanding is that one of the ladies in the film does attempt to swim to surface, to about the 15-foot mark, which would have likely proven fatal for her (depending upon a combination of factors, including how fast she ascended and how much time she had spent down at 150 feet).
The reason you need to ascend slowly, making what divers refer to as “safety stops” along the way, is to allow your body time (at decreasing depths, and therefore decreasing pressures) to gradually expel the extra nitrogen your body absorbs when you breathe air at that depth. And the deeper you go, the more nitrogen you absorb (to the point where, at those depths, it has a narcotic-like effect that clouds your judgement).
Personally, I use a dive computer (with a second dive computer as my backup) to calculate the depth and duration of each safety stop I need to make based on my dive profile (depth and duration) at the time. And I can’t remember how many stops I made coming up from 149 feet, or at what depths, but I do know that I made a couple of them along the way.
I do remember my last safety stop, though, which was around 15 feet. The depth surrounding the Blue Hole is about 18 feet, so I was hovering just above the sandy bottom that surrounds that deep limestone hole in the ocean bottom (it’s a vertical cave that’s about 1,000 feet in diameter and a little more than 350 feet deep). And to add to the excitement, I was also in shark-infested waters.
As I ascended from 149 feet, I spotted a few fish swimming around what appeared to be a circular cloud in the water, just above the mouth of the hole. As I rose closer to it, I began to realize that the cloud was a giant bait ball – a swarm of fish swimming in a tight circle to ward off predators. And those predators, which looked like regular fish from 149 feet below, were actually grey reef sharks – about five feet in length.
Once I reached the mouth of the hole, I cautiously swam over the lip and along the sandy bottom to just beneath our dive boat. I had been in the water around sharks before, but never while they were feeding (this was years before my South African adventure). And it was an exciting sight, right out of a nature documentary, until I realized that I still needed to surface and climb aboard the boat before what was left of my air ran out. That was a little unnerving, because when sharks are in a frenzy like that, mistakes can be made. Fortunately, I made it aboard the boat, along with all my fellow divers, without incident. And our success proves that a slow ascent from that depth, even through shark-infested waters, is indeed a viable option.
Why It Matters
So what’s the big deal? Hollywood has a long history of making movies with ridiculous plots, right?
For starters, I am concerned that this film will reinforce the stereotype that sharks are evil beasts, plotting to kill people like some deranged psychopath. The 1975 film Jaws sparked an irrational fear of – and hatred towards – sharks in the late 70s, which led to several species being hunted to near extinction. And many sharks remain endangered species today, thanks to horrific practices like shark finning, in which the fins are cut from living sharks (to make soup in places like China and Vietnam) and their bodies are then tossed back into the water where they drown, unable to swim without their fins.
This ludicrous plot may also scare people away from scuba diving, which would be an incredible shame. Our oceans are at the front lines of climate change. So, the more people who go diving, the more people will truly appreciate what is at stake – and how bad things already are. Plus, two-thirds of the Earth’s surface is covered by water, so scuba diving is the only practical way to explore the majority of our planet.
Finally, it’s just sloppy filmmaking. With a little effort, or even just learning how to dive, the screenwriter and director could have realized how stupid they now look – and easily adjusted the plot so it at least makes some sense, without losing any of the drama and suspense. In fact, they could have called it 47 Feet Down and gotten the same effect with a far more realistic premise.