THAT NOISE YOU hear while watching "Mermaids" may be the sound of your own tail, squirming and twisting its way through this sea sludge of a caper. Excuse me, make that "free-spirited, coming-of-age comedy," according to Orion Pictures' publicity department.

But this movie, set in the '60s and starring Cher, Winona Ryder and Bob Hoskins, doesn't come of age so much as die of it. It's awash in mediocrity, waterlogged with innocuousness and redeemed only occasionally by sweet-faced Ryder. Screenwriter June Roberts, adapting Patty Dunn's book, creates a limply drawn story with stillborn character development: Misfit-mom Cher heads a wacky, nomadic household consisting of sainthood-obsessed teenager Ryder and swimming-crazy preteen Christina Ricci.

When things get too hot and heavy, either for her daughters at school or herself with men, Cher moves everyone to a different part of the country. Ryder, her nose permanently stuck between the pages of "The Lives of the Saints," wants to be a Catholic nun (and she's Jewish too -- couldn't ya just die?). But she has these sinful, sexually budding thoughts she can't handle. After the family breezes into a small Massachusetts town, Ryder starts to develop a huge crush on local convent caretaker Michael Schoeffling, while Cher becomes the object of shoe salesman Hoskins's affections.

"Please God don't let me fall in love and want to do disgusting things," says Ryder, in the same voice-over narration that worked in "Heathers" but flops here. She's a persuasively gawky girl-woman but those Catholic-guilt, sinful-temptation quips hit you over the head with counterfeit, unceasing cuteness.

Meanwhile, Cher seems to have her mind on other things. She phones in her performance. Hoskins -- the hairiest, shortest, burliest performer currently on screen (I believe Roseanne Barr is taller) -- is so pantomimically endearing, you'll want to throw him to the piranhas.

Speaking of fish, why is this movie called "Mermaids"? Is it the fish-outta-water status the family feels in this button-down, straight world? Is it Ricci's swimming ambitions? The mermaid costume Cher wears for New Year's Eve? Or is it the way the movie flounders from start to finish?

Last and definitely least is the inspiration-free direction of hack-helmsman Richard Benjamin, whose most recent works were "My Stepmother Is an Alien" and the equally insipid "Downtown." He cuts scenes abruptly, encourages the performers to do their one-dimensional worst, and wouldn't know comic timing if someone stuffed a metronome down his throat. He also follows that tiresome studio dictum of supplying a '60s-period pop soundtrack to sum up the era and cut the movie's losses in the record stores. In this case, at least, it makes sound business sense.

MERMAIDS (PG-13) -- Area theaters.