Take ‘47 Meters Down’ with an ocean full of salt

Neal Watson and Jack Levarity on a shark dive in Bimini.
Neal Watson and Jack Levarity on a shark dive in Bimini.

The two pretty sisters on vacation in Mexico were 15 feet under the surface of the ocean in scuba gear while menacing sharks circled around the rickety cage that protected them. Then, there were loud groaning and snapping sounds as the chain holding the cage failed. The cage containing the girls plummeted to the bottom of the sea.

I was watching a scene from 47 Meters Down, a 2017 British film directed by Johannes Roberts, written by Roberts and Ernest Riera, and starring Claire Holt and Mandy Moore.

A few days earlier, while at a doctor’s appointment showing some shark photos I had taken in the Bahamas, a nurse informed me that “scuba diving is dangerous!” “Have you seen the movie 47Meters Down?” she intoned for emphasis.

I decided to watch the movie.

The story followed the two sisters on vacation in Mexico. One of this sister’s boy boyfriend had dumped her because “she made the relationship boring.” The girls went out for a late-night romp on the town and met two local guys who talked them into going on shark cage dive the next day. The thinking was that this would show the jilted sister’s boyfriend that she wasn’t boring and he would regret breaking up with her.

When the sisters arrived at the dock they saw the boat was in bad shape. The dive cage was rusted, held up by thin chains, and was supported by an old crane. The jilted sister was apprehensive but the others assured her that everything would be fine. The jilted sister had never been diving, but the sisters lied to the captain and said both were experienced divers.

When the boat arrived at the dive site, the captain poured a bucket of smelly, bloody chum into the water. The sharks showed up doing their fierce shark glare.

The two local guys went first. No one noticed that the cable supporting the cage had started to fray. The men return unharmed. Now it was the sisters’ turn. Things went wrong and the cage crashed to the sea floor 154 feet below the surface.

Warning: Spoiler Alert!

Now came lots of high drama, all available in sound because the girls were wearing full face masks with audio systems enabling them to talk to each other and the boat’s captain. Audio to the boat was a bit trickier because one of the girls had to come out of the shark infested water to a shallower depth to be in range to communicate with the captain.

Both sisters nearly ran out of air just before two additional tanks arrived. One of the male divers was killed by sharks while trying to bring down extra air tanks. One sister died (presumably after being bitten and dragged away by a shark). And, the surviving sister had a nasty bout of nitrogen narcosis (similar to being intoxicated) from the effects of increased nitrogen intake at greater depths.

At the end of the film the jilted sister survived after being helped to the surface by divers from the Mexican Coast Guard.

As is my habit, I sat critiquing the movie. I know how much influence these diving disaster movies have on many non-divers (such as the staff at my doctor’s office) or even new divers. My wife reminded me, “it is only a movie!”

I responded by pointing out errors about needed safety-stop time (the captain told the girls five minutes), the onset of nitrogen narcosis, air consumption, and how peer pressure is not a good idea in diving. I also grumbled about the dangling alternate air source and split fins (not normally worn by technical or rescue divers) used by the Coast Guard divers and the absence of spare air tanks at various depths for decompression stops.

I mumbled something about no safety briefing, and the apparent lack of first aid supplies including emergency oxygen, which is mandatory to treat many diving accidents including decompression sickness, and the ear pain the sisters would have experience from the rapid descent.

The next morning, I called world famous Keys based underwater photographer Stephen Frink, who is known for the amazing images he has captured of sharks.

Having seen the movie, Frink noted that it had technical errors (including referring to air tanks as “oxygen,” which makes up only about 21 percent of air), but that it might be instructive for folks planning on shark cage diving, which can be “inherently unsafe” unless adequate precautions are taken.

He said that “dive operators in the Keys are regulated by the Coast Guard and marginal operators don’t last too long. “When divers travel, they should research the practices and safety of the dive operators they intend to use,” he advised.

Still chafing about what I felt were the excessive artistic liberties taken in the movie, I visited Pascal Gagneur, general manager of operations in the U.S. for the German rebreather company Submatix.

Every new scuba diver is taught that there are maximum limits, based on time and depth under water, which must be closely monitored to avoid the “bends,” or decompression sickness. If a diver does not adhere to the limits, he or she must stop at specified depths while ascending to the surface.

These so-called decompression stops help the diver’s body remove excess inert gas through respiration. The time length of these stops is based on mathematical models relating to the absorption of inert gases by the human body at the increased ambient pressures found the deeper a diver goes under the sea.

Gagneur holds a pile of diving certifications, has over 8,000 dives, and is very well versed in technical diving. I asked him how long the sisters would have had to decompress based on their approximate time underwater at 154 feet deep.

Not being one to guess, Gagneur typed in a few commands into his laptop and announced: “They would have needed 191 minutes of decompression stops — one minute at 18 meters (59 feet), 7 minutes at 15 meters (49 feet), 12 minutes at 12 meters (39 feet), 20 minutes at 9 meters (30 feet), and 151 minutes at 6 meters (20 feet) — if they were diving on regular air while at 47 meters (154) deep for one hour in the ocean.

What about air tanks actually needed for the dive in the movie? Gagneur calculated that six 80 cubic feet tanks or eight smaller 63 cubic feet air tanks would be needed. The sisters only used two tanks each in the movie.

Gagneur had observations about nitrogen narcosis. He mentioned that many people experience some form of narcosis beyond 118 feet deep and the rate of incidence may be increased depending on the speed of descent and lack of dive experience

The movie 47 Meters Down, even with its inaccuracies, is entertaining. It can be a good primer about what and what not to do when diving. There are steps you can take to ensure you have a safe, fun scuba dive.

Choose a reputable dive operator no matter where you dive. I have been diving in Mexico since 1979 and have found many.

You should have adequate experience for the planned dive unless you are being trained or guided by a dive professional. You need to have the physical ability to handle the dive and should be free of emotional conditions could affect your ability to safely dive. Your gear should be properly serviced. Perform a predive check on your equipment prior to each dive to make sure it is working and that you have the gear you need.

Don’t let others talk you into a dive if you don’t feel comfortable with the planned dive. Besides the disastrous outcomes dramatized in the movie, peer pressure has lead to several undesirable outcomes for divers.

The movie 47 Meters Down, Jaws, and several others portray sharks as man-eating demons. Scientists, however, agree that sharks are vitally important for the well-being of our oceans. Surfers, who statistics indicate are the most at risk of shark attacks, are some of shark’s most ardent supporters. The same is true for scuba divers and the organizations that represent them.

Famed American marine biologist, explorer, author, lecturer, and National Geographic explorer-in-residence Dr. Silvia Earle puts it this way: “Sharks are beautiful animals, and if you’re lucky enough to see lots of them, that means that you’re in a healthy ocean. You should be afraid if you are in the ocean and don’t see sharks.”

Don’t let the movies scare you from experiencing the joy of diving. If you live in the Keys or are just visiting and you are a non-diver you can take a “resort” or introductory course that enables you to conduct a shallow dive under the close supervision of an instructor. If you are lucky, you might even get to see one of the plentiful nurse sharks in the Keys.

Don Rhodes, in addition to a career in government affairs, has taught scuba for 30 years. He and his wife retired to Tavernier five years ago, where he works as an instructor for Conch Republic Divers. He can be reached at donrrhodes@gmail.com.