(Recasts with vessel departure, new throughout)
By Shelby Sebens
PORTLAND, Ore., July 30 (Reuters) - An icebreaking vesselkey to Royal Dutch Shell's plans to drill for oil inthe Arctic departed Portland, Oregon, late on Thursday,navigating between a narrow gap of environmental activistsdangling from a bridge after a two-day human blockade.
Several Greenpeace activists appeared to bow to orders frompolice to lower themselves into watercraft in the WillametteRiver after spending more than 40 hours suspended from a bridgeas temperatures soared over 100 F (30 C).
The Fennica threaded a narrow gap under St. John's bridgejust before 6 p.m. local time (0100 GMT) while several of 13 original activists remained dangling in air, backed by dozens ofkayaks in the river and onlookers in a nearby park who cheeredtheir cause.
Shell aims to return to the Arctic for the first time since2012, when it experienced a series of mishaps including thegrounding of an oil rig.
It is not allowed to start drilling without the Fennica,which is carrying emergency equipment that would cap anyblown-out well, and the drilling season ends in October, whensea ice forms.
Greenpeace says Arctic drilling could be damaging topopulations of whales, polar bears and walrus in the event of anoil spill.
Earlier this month, Shell crew on the Fennica icebreakerfound a 39-inch (1 meter) gash in the hull, possibly caused byan uncharted shoal, and sent it to Portland for repairs.
The icebreaker's departure on Thursday triggered a chaoticwaterborne tussle between law enforcement boats and obstinateactivist kayakers who took to the river again after originallybeing moved to the side by police using loudspeakers.
Police boats made waves that tossed some kayakers overboardand police dragged them into boats.
At least two activists were arrested, Multnomah CountySheriff's Office spokesman Steve Alexander said. Earlier, twoactivists were issued police citations, Greenpeace said.
The activists are the latest group to stage demonstrationsover the past three months, seeking to disrupt Shell ships fromheading north from Pacific Northwest port areas.
On Thursday morning, they successfully forced the Fennica toreturn to a dry dock.
The icebreaker stalled when it neared the bridge on theWillamette, which leads to the Pacific Ocean, met by protesterswaving large red and yellow banners, at times chanting "ShellNo".
"When that ship turned, that was history," kayaker MichaelFoster told Reuters.
Shell spokesman Curtis Smith said the company respects therights of individuals to protest but added "the staging ofprotesters in Portland was not safe nor was it lawful."
As the protests stretched into the afternoon, a U.S. judgein Alaska held Greenpeace in contempt and ordered it to payfines of $2,500 per hour if the protest continued, with finesincreasing daily to a rolling $10,000 per hour after Aug. 2.
It was not immediately known how much Greenpeace would haveto pay in fines, nor if its members planned new protests.
"While we respect the courts, we also respect theincreasingly urgent science that tells us Arctic oil needs tostay underground," Greenpeace USA Executive Director AnnieLeonard said in a statement. (Additional reporting by Timothy Gardner in Washington and EricM. Johnson in Seattle; Editing by Eric M. Johnson, Sandra Malerand Ken Wills)
