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Greenpeace International activists on an inflatable boat pass by The Kremlin while making their way through the Moskva River as they protest against Russia's detention of members of the environmental group in Moscow, Russia, Wednesday, Nov. 6, 2013. Russia's main investigative agency said Wednesday, Oct. 23, 2013 that it has dropped piracy charges against jailed Greenpeace activists and charged them instead with hooliganism, which could still mean years in prison.

SAN FRANCISCO -- Greenpeace's iconic ship the Rainbow Warrior sailed into San Francisco Bay on Friday morning, with plans to hold a 30-hour vigil to support colleagues imprisoned for more than a month in Russia after a protest against Arctic oil drilling.

The Rainbow Warrior unfurled a banner "Free the climate defenders" after docking at Pier 15 near the Exploratorium, according to the ship's media officer, Kat Clark.

The vigil will begin Saturday morning, to support the crew of the Greenpeace ship Arctic Sunrise, who were detained Sept. 19 by Russian authorities after a protest against Arctic drilling. A Russian photographer and a British videographer are also being held.

The "Arctic 30" were initially charged with piracy but the charges were downgraded recently to hooliganism, which carries a sentence of up to seven years. Greenpeace activists are still concerned, however, that the piracy charges have not been formally dropped, Clark said.

Activists from the Arctic Sunrise had attempted to climb the outside structure of the Prirazlomnaya oil rig in the Barents Sea. The Gazprom-owned rig is the first to start production in the Arctic, and Greenpeace maintains there are not adequate precautions for dealing with a massive oil spill.

The Netherlands has asked an international tribunal to order Russia to release the Arctic Sunrise ship and its crew.

Public tours of the Rainbow Warrior will also include information on how palm oil, used in U.S. products such as cookies and cosmetics, is affecting the dwindling numbers of Sumatran tigers.

The latest Rainbow Warrior ship is the newest addition to the Greenpeace fleet and the first vessel to be built for the organization using a crowd-sourcing website.

The ship will be open to the public on Nov. 9, 10, 16 and 17, from 10 a.m. to 5 p.m. Family-friendly activities will be held on both Sundays 10 a.m. to noon.

On Nov. 11, an exhibition featuring "The Art of Resistance" will include more than 70 social justice art activists, live silk screening and graffiti. The event will be held from 12.30 p.m. to 5 p.m.

The Associated Press contributed to this story.

Contact Kathleen Kirkwood at kkirkwood@bayareanewsgroup.com and follow on Twitter.com/kkirkwood.