Part of what makes a thrill ride fun is knowing that it’s a momentary adventure.

The passenger can absorb a quick combination of velocity, twists and a few scares en route to mindless entertainment. Then it’s off to the bumper cars or snack bar.

As the only film series to take its name and concept from a Disney theme park attraction, the sequel “Pirates of the Caribbean: Dead Man’s Chest” is very much like one of these rides. Trouble is that the movie doesn’t know when the ride should end.

At more than two-and-a-half hours, this second installment veers toward overkill. Even with all the creativity and talent concerned, the swashbuckling effort eventually becomes mind-numbing.

Expectations were low in 2003 prior to the release of the original “Pirates of the Caribbean: The Curse of the Black Pearl.” But the picture delivered on all counts, thanks to some spirited direction from Gore Verbinski and a truly eccentric performance from Johnny Depp as loopy Captain Jack Sparrow (which earned him an Oscar nomination).

The flick also grossed more than $300 million stateside, thus ensuring a run of sequels.

With Depp, Verbinski and the rest of the principal cast returning, expectations are now high. In certain respects, these expectations are met. The story of Sparrow searching for Davy Jones’ locker provides the foundation for wall-to-wall action involving cannibals, giant sea creatures, voodoo priestesses, the Flying Dutchman and oodles of swordfights.

As per the first movie, betrothed Elizabeth (Keira Knightley) and Will (Orlando Bloom) find themselves in a pickle because of Sparrow, who always has an ulterior motive for his behavior.

“There will come a moment when you have the chance to do the right thing,” Elizabeth tells him.

Sparrow replies, “I love those moments. I like to wave at them as they pass by.”

The film begins with the two lovers being threatened with execution by the Crown unless they can retrieve an enchanted item that Sparrow keeps on his person. Meanwhile, the fabled Davy Jones (the reliably intimidating Bill Nighy) has come to collect his debt from the captain.

Explaining any more would be pretending to fully understand the enormously convoluted story.

“Dead Man’s Chest” features one of those plots where the hero must find this, then go here. Once there, he must locate something else that will tell him how to go to another place. Factor in that there are multiple heroes on tangential quests, and it’s easy to see why the perplexity of the tale swells with each act.

Where the sequel scores most is in staging elaborate action sequences, which don’t necessitate much thinking on the audience’s part. The first involves an escape from an island of flesh-eating natives in which the captured pirates utilize their circular cage like one of those plastic hamster balls. The second is a three-way duel between Sparrow, Will and former commodore Norrington (Jack Davenport) atop a giant dislodged water wheel. The choreography of these bits is relentlessly clever.

The blockbuster also earns points for its sheer weirdness.

Particularly bizarre (and borderline revolting) are the occupants of the Flying Dutchman. Davy Jones himself has a squid for a head and a crab claw for a hand, and the condemned souls who make up his crew look like byproducts of Dr. Moreau experimenting with an aquarium. There’s a pirate with a hammerhead shark face, and others fused with various fish, crustaceans and all things briny.

It’s hard to tell where the makeup ends and the special effects begin.

“Dead Man’s Chest” is kind of “The Empire Strikes Back” of the series: It builds to a frenetic but unresolved finale that sets up part three, which was shot simultaneously by Verbinski and will be released in May.

Hopefully, that next cinematic ride will be a little more concise.