PUNTA ARENAS/ MADRYN— The Rainbow Warrior III, one of Greenpeace's three ships, is one of the greenest vessels around. It saves energy while sailing. Staff recycles the ship's waste and cook mainly organic meals for the crew.

I came on board for a week's journey from Punta Arenas in Chile, around the Strait of Magellan, to the Argentine port of Madryn. As we prepare to leave, a loudspeaker warns everyone on board that "anyone who does not want to sail should leave the boat now."

The ship's name is a reminder of the dangers Greenpeace vessels have faced in the past. The Rainbow Warrior III protests against nuclear tests, humanitarian crises and, recently, large-scale salmon farming that threatens biodiversity in the world's southern seas. The ship is 58 meters long — 900 tons of steel encases a microcosm of humanity where people must work, meet deadlines and live together in a confined space.

Every morning at 7:30 a.m. sharp, Rita Ghanem, a Lebanese deckhand and one of the three women on board, walks past cabins to wake up the crew. The schedule is rigid. Breakfast is at 8 a.m. Lunch at 12 p.m. Dinner at 6 p.m.

For a relatively small space, it is strange how crew members disappear between meals. Aside from the captain, Pep Barbal, a Spaniard who doesn't speak much, three officers cover the deck in turn, everyone works from 9 a.m. to 5 p.m., Monday to Friday. The chef works until 9 p.m. This routine lasts for three months a year on board, after which crew members go home for about three months.

It is an international crew, so home can mean Lebanon, the Netherlands, Spain, Mexico or Chile. The language on board is English.

On our third day, the wind allows the ship to sail, though moving at a definite angle. Everything then must be done at an inclination: eating, sleeping, dressing. Rubber is used on surfaces to keep objects from sliding. This is normal for the crew but much less for anyone sailing the high seas for the first time.

Barbal explains that the ship has been able to make half of its recent trips by sail alone. Other times, the ship sails 70% or 80% of the time.

It is unusual for a 900-ton ship to move with wind energy alone, chief engineer Antonio Corripio explains to me over the din coming from the engine room. When it does, it means the ship uses just 500 liters of fuel a day, compared to 5,000 liters when the sails are down. The electric engine is necessary for internal functions and lighting, Corripio says.

The vessel treats its waste using bacteria and ultraviolet light, limits the duration of showers, freezes solid waste until docking and recycles all its trash. Chilean deckhand Andrés Soto monitors the separation and classification of trash every morning. The Rainbow Warrior III has ties with people working in recycling at various ports that it docks at.

The sea appears absolutely still one morning, covered by fog. Radio operator Steve Wallace, an Australian, shows me a screen indicating there are three ships nearby. Since 1971, Greenpeace has been sending ships to the world's farthest confines, where there are no authorities to investigate illegal fishing, Wallace says.

This is a mix of work and adventure, and can be addictive, Leonardo Altamira, a Chilean, tells me. He has been a Greenpeace volunteer for 18 years, after leaving his management job at a construction firm.

"The sea gives you a big sense of freedom, of the last frontier and being in a place few have reached," says Emili Trasmonte, an energetic first officer from Barcelona. He used to work in banking and has been sailing with Greenpeace since 2009. He says that with Greenpeace, "you can dream the impossible" — a mentality you need to face "powerful enemies' such as the world's biggest polluters.

Some months ago, when the crew landed on the Chilean island of Chiloé, the ship's Mexican chef, Daniel Bravo, accompanied a local community leader, Teresa, to pick algae. Wading 10 meters into the waters of the Pacific Ocean, they picked luche (sea lettuce), a little-known but edible seaweed. He will mix some of that into a broccoli salad for the 6 p.m. dinner.

Bravo wants his cooking to be sustainable. Luche, he says, is traditionally picked by women and grows back quickly. The seaweed's proteins are more easily digested than animal proteins. A kilogram costs $1 and lasts a month, he says. The ship contacts small-scale suppliers for its food before docking at ports, preferably organic producers. "It is important to encourage small producers," says Bravo, before dropping gnocchi into boiling water.

Before our arrival in Argentina, the sun is nowhere to be seen. But a vigorous wind ensured we arrived on time.

Trasmonte had once told me during a meal that the crew doesn't have much drama in their lives. And yet I could see strong emotions when we arrived and left the Rainbow Warrior III. I thought of a sticker I saw in some corner on the ship that asks, "What if the hippies are right?"