Float on: "Pirates of the Caribbean: On Stranger Tides"

And the shit sailed on. For the revival of the Pirates of the Caribbean franchise, we have to thank the Disney bean counters - who presumably had nothing else to put out this summer - and the increasingly hacky and indiscriminate Johnny Depp, who was reportedly only persuaded to resume his role as Captain Jack Sparrow once reassurances were provided that the Mouse House would fund projects more personal to him than, say, Alice in Wonderland or The Tourist. (Everything's a negotiation nowadays.) In theory, On Stranger Tides ought to be an improvement on third part At World's End, not least as some of the ballast has been tossed overboard: Keira Knightley and Orlando Bloom, for two, have been allowed to drift off over the horizon, a decision which, at this stage, even the actors themselves probably wouldn't bemoan.

Yet if what I hesitate to describe as the organising principle of Part Four is regeneration, fresh starts - not for nothing are the remaining characters on a quest for the Fountain of Youth - the franchise's default position of grotesque indulgence hasn't been entirely abandoned. One early sequence puts Richard Griffiths and Roger Allam in full Regency pomp and finery at a banqueting table stocked high with Marie Antoinette-like sweetmeats: inevitably, these latter go untouched as the performers elect to dine out, all too heartily, on the scenery. At a mere 136 minutes (!), Pirates 4 is at least a more manageable proposition than its predecessors, complacent as they were in the belief everyone on screen and in the audience was having the best of all possible times; its choice is to pile its flab atop one of those thin quest narratives lesser summer entertainments are so enamoured of.

The set-up expands, redoubles once more. Where once there was one crusty sea dog on Sparrow's tail, now there are two: Geoffrey Rush's series veteran Barbossa (somewhat less zombie-ish here than I remember him being elsewhere) and Ian McShane as Blackbeard, arriving very late to the p-arr-ty. Keira and Orblando are replaced by two new young lovers, marginally less simpering if no less ineffectual: a trainee missionary (Sam Claflin) and the mermaid he plucks from the sea (French starlet Astrid Bergès-Frisbey). And there are, momentarily, two Jack Sparrows on screen: the idea Depp's pirate is entirely in love with himself is lent further credence by the sequence that finds him locking first swords, then lips, with a Jack Sparrow impersonator - this turns out to be Angelica, or Penelope Cruz, wearing almost as much eye shadow as Depp himself.

Even with Cruz on board, Pirates' reputation as the ugliest of all modern franchises remains firmly intact. The screen is overrun with grizzled beardies shot against stormy skies or in a below-decks murk, here only accentuated by the innate dinginess of the new digital 3D format. (Is this how the new 3D works, one wonders - by not only refusing to allow us to see its more dynamic effects coming, as in traditional 3D, but allowing us to see nothing very much in the first place?) One or more of the executives affiliated with the franchise must have twigged this, hence the sudden introduction of mermaids to an already cluttered mix, although it's typical of the more-is-more approach that these should be vampire mermaids, played by tastefully topless supermodels: the best mermaids, in other words, that Jerry Bruckheimer money can buy.

At any rate, this surface prettification doesn't come close to addressing the series' underlying racial politics. Parts two and three brought us, in Naomie Harris's voodoo priestess, one of the most retrograde characterisations in recent American cinema. Part four's only part for a black performer is a zombified ship's master, whipping the conscripts aboard the dark vessel McShane - and while there's a degree of irony in the sight of an African-American with slaves of his own, we might perhaps question the characterisation of a black man (even a black zombie) as someone who's just really angry. I'm not saying these films should be rewriting maritime history, but would it be too much for the company that gave the world Song of the South to exercise a little sensitivity in what's likely to become their most watched release of the year?

Perhaps it doesn't matter; perhaps, at this stage, seeking qualitative fixes from a Pirates of the Caribbean movie is as howling from the rigging into a force-10 wind. Any adjustment would be mere tinkering with a formula that's proven fundamentally mediocre, when not aiming squarely for the lowest common denominator. With Gore Verbinski at the helm, these movies got bigger and bigger, and he may have jumped ship upon realising nothing he could do with Part Four would top the preposterous swordfight he staged on a giant waterwheel in Part Two.

His replacement Rob Marshall, the choreographer of Chicago and Nine, gives us false hope early on in making one action setpiece entirely about the recovery of a choux bun, suggesting this instalment may be predisposed to smaller things, or at the very least a demonstration of state-of-the-art Hollywood catering. Thereafter, alas, Marshall resigns himself to going through the motions, as everybody gets bogged down in a jungle that makes a nonsense of the subtitle: he sets up a swordfight every fifteen minutes between a dozen or more characters, none of whom you feel compelled to give a single hoot about, and generally moulds something utterly lacking in shape, variety or even a climax, save a teaser for the inevitable Pirates V.

Around the halfway mark, I began to develop a sneaking (and wholly unexpected) respect for the way At World's End really went for it, pushing the franchise, and trying the audience's patience, about as far as it could conceivably go. Compared to that near-avant-garde experiment in tedium, On Stranger Tides is merely prosaic: it leaves you wondering only how something so vast and relatively expensive could end up quite so dull and affectless. We get precisely one surprise, which in the name of saving you time and money, I shall reveal here: a maybe fifteen-second cameo from a corseted Judi Dench, sitting in the back of a carriage Depp is propelled into at one point. "Is that it?," Dame Judi asks, shortly before being shuttled away off-screen and handed her (no doubt sizeable) paycheque. Lady, I couldn't have put it better myself.

Pirates of the Caribbean: On Stranger Tides is on nationwide release.