For three years they relied on the stars. Without modern navigational instruments, the ocean swells and birds were used to guide them. Navigators had to memorise the nightly courses of more than 200 stars, along with their precise rising and setting locations on the horizon.
This weekend, after a three year, 19 country, 40,000 nautical-mile journey, the crew of a Polynesian canoe finally sailed back to Hawaii’s shores, having taken its message of the importance of preserving traditional cultures around the world.
"We really are sailing in our ancestors' wake," said Ka'iulani Murphy, 38, an apprentice navigator on the canoe.
"We had to re-learn what our ancestors had mastered."
For much of the 20th century, anthropologists assumed the thousands of far-flung islands of the Pacific were settled after being accidentally found by sailors who were driven off course by storms.
But native Polynesians have long argued, based on their oral traditions and nautical lore, that settlement was the result of deliberate journeys of exploration and colonisation undertaken by highly skilled navigators.
“For centuries, Europeans stubbornly refused to acknowledge Polynesian achievements because they simply could not believe that a so-called primitive society was demonstrably better at navigation than they were,” said Wade Davis, explorer in residence at the National Geographic Society.
The voyage perpetuated the traditional wayfinding that brought the first Polynesians several thousand miles to Hawaii, hundreds of years ago, and also helped train a new generation of young navigators.
Arriving back in Hawaii on Saturday, accompanied by a fleet of smaller canoes, the team completed the first-ever round-the-world voyage by a traditional Polynesian vessel—a predecessor of the modern catamaran.
In a canoe named Hokulea, which translates as star of gladness, the 17-member crew had rotated on and off the vessel, in month-long stints.
The canoe was built and launched in the 1970s, when there were no Polynesian navigators left on Hawaii.
So the Polynesian Voyaging Society looked beyond Polynesia to find one, and eventually tracked down Mau Piailug, from a small island called Satawal in Micronesia.
He was among the last half-dozen people in the world to practice the art of traditional navigation, and he agreed to guide Hokulea to Tahiti in 1976.
"Without him, our voyaging would never have taken place," the Polynesian Voyaging Society said on the website for Hokulea.
"Mau was the only traditional navigator who was willing and able to reach beyond his culture to ours."
This time the Hokulea set out to inspire a new generation of navigators and spread a message of “malama honua”, or caring for the earth.
Native Hawaiian ancestors were not only skilled navigators but also good stewards of the islands, who farmed and fished sustainably.
"They figured it out - how to live well on these islands," said Nainoa Thompson, president of the Polynesian Voyaging Society.
"And I think that is the challenge of the time for planet earth and all of humanity."
The crew were forced to be environmentally sustainable, supplementing their packaged foods and water with fish they caught during the voyage and rainwater.
The fish they caught for meals never went to waste, even when the crew once landed a 49-pound ahi.
"The fish was plenty for us for that day," wrote Naalehu Anthony, a crew member who participated in several legs of the voyage, in a blog post.
Crewmembers slept in plywood bunks covered with waterproof canvas.
Bathing was simple, recalled Russell Amimoto, a Hokulea crewmember for two legs.
"We have unlimited supply of nice, ocean-temperature saltwater available," he said, explaining that crewmembers threw a bucket attached to a rope overboard to scoop up water for showers.
The voyage has had challenges and reaching South Africa in 2015 - the journey's halfway point - was the most dangerous leg because of complicated ocean conditions.
Last week the crew spotted the 10,023-ft high Maui mountain Haleakala looming in the distance, signifying Hokulea's official return to Hawaii waters.
David Ige, the governor of Hawaii, welcomed the Hokulea and its crew back during the homecoming ceremony.
“Watching you on your epic voyage, you taught us that there is more than connects the world than divides us,” he said.
He spoke of how the voyage had inspired the sustainability movement and received a standing ovation when he reminded the crowd that last week Hawaii became the first state to commit to the Paris Climate Agreement.
Kirk Caldwell, mayor of Honolulu, then presented Mr Thompson with a ceremonial key to the city.
“Watching the canoe come in, I think many of us had tears in our eyes,” he said.
Hokulea will now embark on an eight-month trip sailing throughout the Hawaiian islands.
"We will go to as many as 70 communities and 100 schools to thank Hawaii's people and share what we have learned with their children," said Mr Thompson.
"We are also looking forward to hearing Hawaii stories of malama honua.