The captain is curt but dutiful. The first mate has a mischievous twinkle in his eye and a Cheshire cat grin. He and his burly and very bearded crew are worldly roughnecks, more inclined to stomp and clap than pray. Then there are the two landlubber brothers, fresh-faced and sunshine voiced, one loving God and the other adventure.

Each, in“Swept Away,”might think he knows what manner of man he is, just how good and how bad. There’s comfort and convenience in claiming a moral identity, but also privilege. Even the bandit who has long accepted his own villainy, this world-premiere musical says, just hasn’t been tested yet.

The show opened Thursday, Jan. 27, atBerkeley Repertory Theatreafter several COVID delays, including a one-week opening night postponement. It has a starry creative team in director Michael Mayer (“American Idiot,”“Head Over Heels”), librettist John Logan (“Red”) and the Avett Brothers, from whose folk-rock catalog the music and lyrics hail. As this team looks to shop the piece to still larger stages, that moral conundrum is its strongest asset: When a whaling voyage goes horribly awry, how far would you go to stay alive? Is survival worth it if you have to live with what you’ve done?

In its current incarnation, the show, even at a lean 90 minutes, takes an awfully long time to paddle out of the backstory’s whirlpool into the present tense. It establishes, re-establishes and re-re-establishes how Big Brother (Stark Sands) and Little Brother (Adrian Blake Enscoe) just fell off the turnip truck; how they’re not “natural mariners”; how they honor their parents, the farm, their god; how much Little Brother misses his girl. The exposition of the Captain (Wayne Duvall) is so flowery — “What are we but useless men hunting vanishing prey in a dying trade?” — as to become a red herring. Is “Swept Away” about to sail into “Moby-Dick” territory?

The jukebox musical form is a culprit here too. When songs were not originally written for the purpose at hand, they frequently declaim or belabor rather than drive. A director of Mayer’s caliber doesn’t need a whole song to make clear that a sailor is a “hard, hard worker every day.”

And too often the tone of the Avett Brothers’ songs is so wildly at odds with what’s happening in a scene as to break its meticulously cast spell.

At rise, as the mate (John Gallagher Jr.) has a nightmare flashback, the cheerful banjo of “Go to Sleep” that pipes in sounds like a ghastly mistake. To be clear, a contrast of tones can be a ripe theatrical device, and that number’s dark lyrics are a closer fit to the show’s first moments. But Mayer doesn’t achieve that directorial magic that makes accord of apparent discord.

But once the vessel hits choppy waters, the show rights itself. Rachel Hauck’s whopper of a set design makes three-dimensional “Tetris” of a tuberculosis ward, a whaler deck, a tempest and open water, with a reveal grander and more magical than anything millions of dollars in CGI could create. Kevin Adams’ canny lighting design can create the illusion of a waterline on the ship’s hull or help turn the dying into ghosts.

The cast is ace too.

Gallagher composes a whole melodic line within one-syllable spoken words, activating his whole body to his task in a way that makes him seem more alive than the rest of us.

Enscoe surrenders himself fully to the song “No Hard Feelings” (one of the few numbers that add to the story rather than merely illustrate it), with a true stage actor’s ability to make everything around him turn heavenward.

Eventually, the survivors must make a horrible decision, and “Swept Away” and Berkeley Rep merit kudos for not shying away from the worst of human nature, for exploring in good faith and in depth what many of us would prefer not to ask of ourselves. If the show’s resolution is more black-and-white than its complex buildup, “Swept Away” nonetheless elevates a tragedy to mythic proportions, with characters’ suffering reverberating all the way into your own core, which might be hollower than you think.

M“Swept Away”:Book by John Logan. Music and lyrics by the Avett Brothers. Directed by Michael Mayer. Through March 6. 90 minutes. $42-$268, subject to change. Berkeley Repertory Theatre, 2025 Addison St., Berkeley. 510-647-2949.www.berkeleyrep.org

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