Last year, as they entered their first season homestretch, the writers of “Fear the Walking Dead” tried to figure out what to do with the show’s survivors. There was a vague plan to hole them up on the coast in the home of a mysterious wealthy character named Victor Strand as the zombie apocalypse unfolded. But from there … what? Drive north? South? Head for the desert?

Then, the series showrunner Dave Erickson recalled, “we said, ‘What if he had a yacht?’”

From that spark came a blueprint for a very different “Fear the Walking Dead,” returning to AMC on April 10. A tense urban drama in its six-episode first season, this West Coast spinoff of “The Walking Dead” is taking to the high seas for Season 2, uprooting both the story and the production as it sets sail on a yacht. The boat will be the main setting for many episodes, which take their cues as much from thrillers like “Dead Calm” and “Knife in the Water” as from horror fare. There will be zombies, of course, but the greatest menace will be marauders and other seafaring survivors.

It seems counterintuitive to overhaul a show that is already doing well. “Fear the Walking Dead” hit the ground running last summer, notching the highest-rated debut in cable history. The episode total jumps from six to 15 this season, a tougher lift even before the series, which shot in Los Angeles and Vancouver last season, decided to relocate to another country.

The new direction required that the company move to Baja Studios in Rosarito, Mexico, where movies like “Titanic” and “All Is Lost” were filmed, and build a boat in six weeks. For the actors, there was yacht training and flailing swim tests that left them commiserating over margaritas and wondering what they’d gotten themselves into. “We were all disappointed in our skills,” said Colman Domingo, who plays Strand. “At some point I started doing like a doggy paddle, then a backstroke — I didn’t know what I was doing anymore.”