Lions, dragons, a big, nasty, water-snake and minor self-doubts. The Chronicles of Narnia: Voyage of the Dawn Treader buoys up the tradition of British children saving an uncharted, parallel fantasy world.

Decades of Narnia time equals mere minutes of present time. So when in Dawn Treader the younger set of the Pevensie siblings — Lucy and Edmund (Georgie Henley, Skandar Keynes) — return to Narnia, the chic-looking Ben Barnes (now King Caspian) barely has a grown man’s beard.

In The Lion, the Witch and the Wardrobe, the gateway to Narnia was an old, secluded wardrobe cabinet in a secret room. When Prince Caspian came, the children were blown to Narnia by a horn. Now it’s a painting that turns Niagara Falls. And it all happens fast thanks to the ham-fisted, scrunching job by Narnian-first timer Michael Apted.

“I didn’t notice it before, but the ship looks Narnian,” says Lucy, peering into a maritime painting with a small boat fighting the waves. Within seconds she, Edmund and their squirmy cousin Eustace Scrubb (Will Poulter) drown in clear water and transition in front of The Dawn Treader, a royal-looking mid-sized ship with a crew of man and man-beasts that eventually gets coiled up by a computer-generated sea serpent.

But before that, there is a rudderless un-magical telling about seven swords, seven misplaced lords (three of them are found sitting frozen at a table) and forgotten islands. There is an ill-omened green mist that kidnaps people; a pool of water that turns the greedy to gold; invisible hopping dwarfs with a genetic foot deformity and an amulet that turns Eustace to a teary-eyed dragon.

Dawn Treader falters and foils before ending as a TV-special episode (with a $140 million budget) and oodles of Christian subtext.

Aslan — the big, furry coated lion who speaks in Liam Neeson’s tone — is there. The Dark Island with its sinister travelling mists and the look of Skull Island is irrefutably hell. While Lucy frequently doubts if she will blossom into beauty, big sister Susan is now too old for Narnia. Edmund vexes about playing second fiddle to Caspian, and he gets his wonted pill of diffidence when Tilda Swinton returns for a scene as the White Witch, all misty and floating.

The only one not in doubt is Reepicheep, the hero-hearted mouse who walks upright, talks regally and brandishes a slim mouse-keteer sword.

Voiced by Simon Pegg, Reepicheep — and Aslan — are the films’ epitaphs. For a fantasy it’s plain dumb sailing.

Released by 20th Century Fox, Chronicles of Narnia: Voyage of the Dawn Treader is rated PG-13. Prince Caspian was flawed, but better.