SAN FRANCISCO — Banking heir David de Rothschild is sailing across the Pacific Ocean on 12,000 plastic bottles.

The discarded containers were made into a catamaran called the Plastiki, which is heading for the Line Islands, 1,300 miles south of Hawaii, on a mission to showcase recycling. The crew includes two grandchildren of the late Norwegian adventurer Thor Heyerdahl, of Kon-Tiki fame.

“I wanted to get people to think sensibly that waste isn’t really waste, but merely inefficient design, and that we can turn it into a resource,” de Rothschild, 31, said by satellite telephone as the boat sailed west from San Francisco. “Every day, we are seeing bits of trash floating past us. They look like jellyfish, but then we realize they are plastic bags.”

The Pacific is littered with trash, including one mass of swirling plastic at least 1,000 miles across, said Charles Moore, an oceanographer who identified the conglomeration in 1999.

Marine debris kills sea turtles, seals and sea birds and destroys coral reefs, said Timothy Ragen, executive director of the U.S. Marine Mammal Commission.

The trip is an outreach of de Rothschild’s London company, Adventure Ecology, which advocates for environmental causes including ocean cleanup.

De Rothschild, son of British financier Evelyn de Rothschild, descends from the 18th-century European banking family that once held the largest private fortune in the world, according to “The House of Rothschild: Money’s Prophets,” by Niall Ferguson.

His forebear Mayer Rothschild began the banking dynasty in Frankfurt and expanded to Vienna, London, Naples and Paris with his five sons.

“Rothschild is international,” said Seba Sheavly, a marine scientist in Virginia Beach, Va., and consultant for the National Oceanic and Atmospheric Administration.

“He’s calling attention to the most precious resource on the planet and how we’re not treating it very well.”

De Rothschild said the Plastiki name pays homage to Heyerdahl’s Kon-Tiki, a balsa raft he sailed from South America to Polynesia in 1947.

That voyage tested a theory that indigenous peoples migrated across the ocean before Europeans landed in the Americas, Heyerdahl wrote in his 1950 book, “Kon-Tiki.”

Heyerdahl’s grandson Olav, 32, and granddaughter Josian, 26, are crewing on the Plastiki, along with a captain, videographer and first mate.

At 60 feet, the Plastiki isn’t large for an oceangoing vessel. It has encountered rough seas and a curious shark since leaving San Francisco on March 20 for the 3,400-mile trip to the Line Islands, de Rothschild said.

“All the crew members had to be clipped on to every part of the boat so we don’t get washed over the side,” he said.

Weather changes quickly and sea temperatures are cool this time of year, said Jo Royle, 30, the captain and a racing sailor. The Plastiki is stocked with dried meats, fruits and vegetables, and three liters of water per person per day, she said.

Plastiki’s crew will study coral reefs, sharks and how the local population is coping with globalization on Fanning Island, or Tabuaeran, its first stop in the Line Islands. The final destination is Sydney, 4,100 more miles.

It took a year to assemble the Plastiki’s bottles into a seaworthy craft. The boat has two hulls and five sails and travels at an average speed of five knots. That’s about 6 miles per hour.

“It’s a little slower than I’m used to,” said Royle, the captain.