"What do you mean you want to get out and walk?"

Remember the Robert Redford movie “All Is Lost,” where he was stranded at sea? “Adrift,” with teen-romance veterans Shailene Woodley (“The Fault in Our Stars”) and Sam Claflin (“Me Before You”) lost in the Pacific on a storm-damaged yacht, is like that, only boring. It’s based on real events recounted in Tami Ashcraft’s book “Sky in Mourning: The True Story of Love, Loss, and Survival at Sea” — and being anchored to history is what drags it down.

We begin in medias res, with Tami (Woodley) regaining consciousness below decks in a sinking boat and screaming for Richard, who is nowhere to be found. It’s a gripping way to open a story, dramatically shot at sea by Icelandic director Baltasar Kormákur (“Everest”), but it’s immediately deflated by the jump back to five months earlier, before anything interesting had happened.

It’s 1983, and 24-year-old San Diego surfer girl Tami is bumming around the world, hanging out in Tahiti when she meets Richard (Claflin), a gentlemanly English sailor with similar levels of leisure time. The rest of the film cuts back and forth between Tami and Richard’s courtship in Tahiti and the “present,” where Tami finds a badly injured Richard clinging to a lifeboat, pulls him onto the moribund yacht, and tries to keep him (and herself) alive until rescue, which may never come.

Most of the material set on the yacht is vivid and compelling enough until we get to the stage where they’re just driftin’ for days on end, which is tedious. But everything that takes place before Richard and Tami set sail feels extraneous — not just because we know nothing truly exciting is going to happen until they’re on the water, but because their meeting, courtship, and romance are utterly mundane. The only interesting thing about these people is that they’re lost at sea. You don’t have to show us what happened to them before they became interesting.

Part of what made “All Is Lost” work so well was that it provided no context. We didn’t even know the guy’s name, let alone why he was at sea or what he’d left behind. All that mattered was the present conflict of Man vs. Nature. That’s all that matters in “Adrift,” too, so it’s counterproductive to pad out the runtime with flashbacks that don’t add anything to our understanding of the characters or their predicament. Just get to the part where they have to drink pee already!

Crooked Marquee

C (1 hr., 36 min.; PG-13, a little profanity, some grisly medical images, partial nudity.)