“47 Meters Down”

**1/2

(PG-13, 1:29)

We’re going to need a bigger cage.

The “Jaws” jokes write themselves with “47 Meters Down,” a surprisingly effective shark-in-the-dark thriller that makes for frighteningly fun summer escapism. Horror director Johannes Roberts (“The Other Side of the Door”) knows what the audience wants in a film like this — two sisters trapped in a dive cage surrounded by sharks — and gives it to them, straight no chaser.

Appropriately, he wastes little time on exposition. Lisa (Mandy Moore) and Kate (Claire Holt, “The Vampire Diaries”) are two Americans on vacation in Mexico. Uptight Lisa is trying to deal with a bad break-up, inspiring younger Kate to take her out on the town to drown her romantic sorrows and stop sulking.

That’s where they meet two good-natured, good-looking locals — Benjamin (Santiago Segura) and Louis (Yani Gellman) — who convince them that they need to dive with sharks to make their trip really memorable. These guys just happen to know a boat captain who, for a little cash, will take them out to the right spot.

Lisa is reluctant but Kate is totally up for hopping on a sketchy boat run by a scraggly expat American (Matthew Modine) — who looks like he’s on the run from several U.S. governmental agencies — with two random dudes they just met while dancing and wearing beer goggles.

Guess they didn’t see last summer’s shark movie, “The Shallows,” because before you can say Shark Week, Lisa and Kate are in a cage underwater marveling at the beauty of all the fish. Just when Lisa is starting to think her fears are unjustified, a mechanical mishap sends the metal box plunging into the depths and the captain can’t immediately reel them back in. That’s when the oohing-and-aahing quickly turns to panic and pleading.

Working from a script he wrote with Ernest Riera, Roberts keeps ramping up the tension and it mostly works, even when a plot device or two might seem to contradict common sense. Coming in at a breezy 89 minutes, the film doesn’t allow much time to dwell on them anyway.

On top of that, “47 Meters Down” is a technical marvel. The first film to be shot in the 60,546-square-foot water tank at the Pinewood Dominican Republic Studios, it absolutely makes members of the audience feel like they’re at the bottom of the ink-black ocean with Lisa and Kate. And the sharks look real and really hungry.

The movie lacks the emotional resonance of that other stranded-in-the-ocean cinematic experience, “Open Water,” from 2003. That was a film that lingered in the memory long after the lights went up, partly because it was based on a true story about a couple whose dive boat left them to perish in the middle of the sea. And “47 Meters Down’ is no “Jaws,” but it doesn’t aim for camp like the “Piranha” movies either and feels less voyeuristic than did “The Shallows.”

None of that makes “47 Meters Down” any less entertaining and unsettling in a popcorn-thriller way. Like the old ad for “Jaws 2” said, “Just when you thought it was safe to go back in the water … ”