SEATTLE — Thousands streamed into a Seattle waterfront park Friday for the opening of a three-day marijuana festival — an event that is part party, part protest and part victory celebration after the legalization of pot in Washington and Colorado last fall.“This is going to be the biggest year for Hempfest,” said Jack Beattie, an 18-year-old Seattle University student, as he shared a joint with two friends. “In past years, people were a little bit sketched out about smoking in public. Now, there’s going to be a lot more.”The free annual event was expected to draw as many as 85,000 people per day. On Friday, many strolled by vendor stands, joints in hand as they checked out colorful glass pipes, tie-dyed clothing, bags of “ideal cultivation soil,” and hemp wares, including purses and necklaces.Others sprawled on the grass in the steamy sunshine, listening to bands and speeches, or lit bongs on the beach and watched ferries cross Elliott Bay.Hempfest is in its 22nd year of advocating for the legalization of marijuana, and this is the first time it’s been held since last fall, when Washington’s voters approved Initiative 502 and Colorado’s passed Amendment 64, legalizing the possession of up to an ounce of pot by adults over 21. Both states are developing systems of state-licensed growers and processors, along with stores where taxed, regulated weed will be sold.