Entertainment

Dialogue’s waterlogged

The good news on “Sanctum” is that it is merely exec-pro duced, not written, by James Cameron. The bad news is that it sounds like it was written by the star pupils at the Cameron Academy of Screenwriting.

“Sucks to be you,” “This cave will kill you in a heartbeat” and “Are we gonna do this? Or are we just gonna talk about it?” are typical lines in a movie about divers who (for some reason) are exploring caves 2,000 meters below the surface in Papua New Guinea. They seem to care about where the cave network will lead them, but no one on-screen ever furnishes any reason why we in the audience should, and “Sanctum” turns out to be as gripping as plankton.

This 3-D movie, which has some nifty effects and graphics and the occasional pretty tableau, nevertheless is just a dolled-up ’70s disaster movie in which the only reason to stick around till the end is to find out who in the cast will triumphantly live and who will colorfully perish.

But as the divers deal with a flood that cuts off their route to the surface and forces them deeper, “Sanctum” doesn’t stand up so well against “The Poseidon Adventure.” Shelley Winters and Gene Hackman were rousing and memorable, in their ridiculous way. This movie features the dismal likes of Australians Richard Roxburgh and Rhys Wakefield as a father-son team of tough guys bonding through episodes of manly peril.

Roxburgh, for all his growly badinage, isn’t fit to carry Lee Marvin’s cigar box, while Wakefield’s incessant, incandescent smiling suggests he thinks he’s doing “Mamma Mia!” instead of an undersea adventure. The best actor in the piece is the journeyman Ioan Gruffudd, best known as the elastic man from “Fantastic Four.”

Cameron, to his credit, doesn’t make boring movies, and if he were in charge you could count on him to at least produce some clammy monsters and/or evil corporations to give the heroes something to do besides churn through the murk. Instead, director Alister Grierson treads water. His cast confronts dumb dangers like cowards going nuts (really, if you were thousands of feet below the surface, would you attack the ablest diver in your group?) and lady divers coming down with severe attacks of the girlies, in one case because her hair gets caught in a chain. One character’s doom is telegraphed with such blaring obviousness that I was reminded of a Mad magazine spoof of “The Shining” in which the Scatman Crothers figure wore a button labeling him “token victim.”

A symbolically important flashlight (or “torch,” in Australian) is pulled out at the exact moment when it is guaranteed to be unintentionally hilarious, its teeny-tiny wattage instantly lighting up 50 million gallons of black water like the red carpet of a movie premiere.

The script keeps trying to talk us into being awed and fascinated by this clunky spelunking, the writers sounding like stock pitchmen hawking shares in Macho Men, Inc. “Carl likes to play by his own rules.” “Frank, you are one stubborn son of a bitch.” “It was the most heroic goddamn thing I’ve ever seen.”

I didn’t expect Tom Stoppard-level writing. But nor did I expect to long for the relative panache of Sly Stallone.

kyle.smith@nypost.com