Sisters’ sinking feeling trapped with sharks

June 16, 2017

The underwater thriller “47 Meters Down” works so well as a nail-biting example of nonstop tension for one reason: its matter-of-fact credibility.

The simplicity with which English director (and co-screenwriter) Johannes Roberts presents his terrifying tale of two sisters trapped in a shark cage 47 meters (approximately 155 feet) down is the film’s greatest effect.

The sisters are on a Mexican vacation where Lisa (Mandy Moore) continues to blame herself for a recent breakup. Lisa’s ex has found someone younger and not so staid.

If Lisa is the sensible, grounded adult, younger sister Kate (Australia’s Claire Holt) is her party-hearty, live-life-to-its-fullest opposite.

Kate convinces Lisa to take a local shark sightseeing excursion. In scuba gear with oxygen tanks, they will be protected in a shark tank lowered just five meters in the water. Pictures! Thrills!

Lisa sidesteps regulations that require some underwater experience. She’s going not for the thrills but to prove to herself that she can be spontaneous.

The boat captain (Matthew Modine) follows procedure and cautions the two about the “bends,” the fatal effect possible after coming up from deep water too fast without depressurizing along the way.

Once they begin their descent, a cable snaps and suddenly, as the title declares, they are on the seabed floor, 47 meters from fresh air and safety.

With sharks circling their cage, getting out and swimming slowly to avoid the bends is not a healthy option. But their oxygen can last only so long.

“I’m scared,” Lisa moans, repeatedly. Of course she is — and so are we.

There is no malevolent psycho, eager to torture a couple of beautiful tourists. There’s no one to blame. That’s powerfully potent.

Unlike last summer’s “The Shallows” — in which Blake Lively starred in a fantastical, no-relation-to-reality woman vs. shark thriller — what happens here is all so terribly, easily possible.

(“47 Meters Down” with its virtually nonstop intensity will be too much for some children.)