This is how effective Adrift is: I sat through it telling myself, “It’s only a movie ... it’s only a movie ... it’s only ...” And when that failed, I thought about my own personal terrors: the nightmare of being buried alive, sudden amnesia, having sex with Idi Amin. Nothing worked. There I was, a supposedly cynical and sophisticated seen-it-all film critic, reduced to a sweaty, nervous wreck, squirming in his seat.

From the posters and trailers you’ve seen, Adrift might look like a film trying to cash in on the surprise success of Open Water (2003) — you know, the “true story” of that couple who got left behind when out scuba-diving. Adrift also claims to be based on “true events”. It has not one but three couples bobbing about in the sea. And it’s even called Open Water 2 in America and parts of Europe. But Adrift is the better of the two films.

It takes a simple situation — six people stranded in water — and weaves a more complex and intriguing story about character and friendship.

After a period of five years, six American friends meet up again to go sailing on a yacht off the waters of Mexico. There’s Amy (Susan May Pratt), her husband, James (Richard Speight Jr), and their baby girl, Sarah. Then there’s the rugged Zach (Niklaus Lange) and his tough-minded girlfriend, Lauren (Ali Hillis). They arrive at the yacht to find their host, Dan (Eric Dane), in bed with bimbo-ish blonde Michelle (Cameron Richardson).

So, off they sail for a wonderful weekend. They put down anchor and pour down the beer. Talk flows, and a small undercurrent of personal tensions starts to surface. Michelle is the object of male desire and female contempt. Dan and his yachting lifestyle are a source of admiration and envy. They all decide to go for a swim, except Amy. She suffers from a fear of water, having seen her father drown as a child. But Dan grabs her and leaps into the sea. The prank misfires. Amy is traumatised, then they make a discovery — the ladder that will let them back onto the boat hasn’t been lowered. The ship’s slippery hull makes it impossible to crawl back up.

Whereas the couple in Open Water were clearly grown-ups who were victims of an accident, the Adrift crowd are more like irresponsible teenagers who have nobody to blame but themselves. It is the immaturity of Dan that starts the chain of disastrous events; it’s the immaturity of the others that prolongs it. The friends have to survive something almost as deadly as hungry sharks: each other. The solidarity they badly need starts to sink under the weight of accusations, recriminations and fits of temper.

Adam Kreutner and David Mitchell’s screenplay is clever. Having the yacht right there, in reach but unattainable, among the floating, desperate friends makes it a source of torment and hope. And in choosing to shoot the film with a handheld camera, the German director, Hans Horn, manages to create a real intimacy with his characters. We are up close, personal and wet — or so it feels. It is here in the water that we see for the first time who these people really are.

Once in the water, Horn tickles your anxiety, strokes your darkest fears and gives your heart a long, hard squeeze for the next 70 minutes or so. A more obvious director might have gone for the easy option of sending in the sharks. Instead, he knows that thanks to other film directors — take a bow, Mr Spielberg — we already have shark fear in the back of our minds, so it’s never shown on the screen.

Horn’s ace card isn’t a shark: it’s a baby. When baby Sarah wakes up from her nap, she is hungry and starts to scream, which Amy can hear, coming across loud and clear over the baby monitor. So we have the prospect not only of six people drowning, but of a baby slowly dying from hunger.

The film then becomes a mother’s tale of having to save her baby, her husband (he has a terrible head wound) and herself. It’s dramatically cheap, but by God it works.

Films like Adrift appeal to us, it is said, because they explore our primal fears about our capacity to survive and save our loved ones. And the film does offer a kind of weird audience participation, in that you have to figure out how you would behave. But I wonder if that primal-fear stuff is just an alibi for the secret delight we take in watching people who get to go on wonderful yachting trips suffer? After seeing Adrift, a weekend at Butlins looks pretty damn good.

Adrift, Four stars
15, 95 mins