ON THE GULF OF MEXICO (AP) — Crews planned Sunday to park the giant oil containment box on the bottom of the Gulf of Mexico, and offload equipment that could be used in a new attempt to stem the flow of gushing into the sea.

The equipment to be offloaded from another vessel would use a tube to shoot mud and concrete directly into the well’s blowout preventer, a process that could take two to three weeks. But BP PLC spokesman Mark Proegler said no decisions have been made on what step the company will take next.

The company was considering several options, including the technique known as a ‘‘top kill,’’ Proegler said.

Crews planned to secure the big box about 1,600 feet from the massive leak site, much farther away from where it was placed Saturday after icelike crystals clogged the top when it was over the leak, according to a daily activity sheet reviewed by The Associated Press.

It could be at least a day before BP can make another attempt at putting a lid on a well spewing thousands of gallons of crude into the Gulf each day.

Waves of dark brown and black sludge crashed into a boat in the area above the leak. The fumes there were so intense that a crewmember of the Joe Griffin and an AP photographer on board had to wear respirators while outside.

On the deck, a white cattle egret landed, brownish-colored stains of oil on its face and along its chest, wings and tail.

The company’s first attempt to divert the oil was foiled, its mission now in serious doubt. Meanwhile, thick blobs of tar washed up on Alabama’s white sand beaches, yet another sign the spill was spreading.

It had taken about two weeks to build the box and three days to cart the containment box 50 miles out and slowly lower it to the well a mile below the surface, but the frozen depths were just too much. BP officials were not giving up hopes that a containment box — either the one brought there or another one being built — could cover the well. But they said it could be Monday or later before they decide whether to make another attempt to capture the oil and funnel it to a tanker at the surface.

‘‘I wouldn’t say it’s failed yet,’’ BP chief operating officer Doug Suttles said of the containment box. ‘‘What I would say is what we attempted to do … didn’t work.’’

Early Sunday, there was little visible new activity at the site of the oil spill. The skies were clear, but the waves on the sea were kicking up and the wind was more breezy than in previous days.

There was a renewed sense of urgency as dime- to golfball-sized balls of tar washed up Saturday on Dauphin Island, three miles off the Alabama mainland at the mouth of Mobile Bay and much farther east than the thin, rainbow sheens that have arrived sporadically in the Louisiana marshes.

‘‘It almost looks like bark, but when you pick it up it definitely has a liquid consistency and it’s definitely oil,’’ said Kimberly Creel, 41, who was hanging out and swimming with hundreds of other beachgoers. ‘‘… I can only imagine what might be coming this way that might be larger.’’

About a half dozen tar balls had been collected by Saturday afternoon at Dauphin Island, Coast Guard chief warrant officer Adam Wine said in Mobile, and crews in protective clothing patrolled the beach for debris. Authorities planned to test the substance but strongly suspected it came from the oil spill.

In the nearly three weeks since the Deepwater Horizon rig exploded April 20, killing 11 workers, about 210,000 gallons of crude a day has been flowing into the Gulf. As of Sunday, some 3.5 million gallons had poured into the sea, or about a third of the 11 million gallons spilled in the Exxon Valdez disaster.

Until Saturday none of the thick sludge — those indelible images from the Valdez and other spills — had reached shore.

It had taken more than 12 hours to slowly lower to the seafloor the peaked box the size of a four-story house, a task that required painstaking precision to accurately position it over the well for fear of damaging the leaking pipe and making the problem worse. Nothing like it had been attempted at such depths, where water pressure can crush a submarine.

Company and Coast Guard officials had cautioned that icelike hydrates, a slushy mixture of gas and water, would be one of the biggest challenges to the containment box plan. The crystals clogged the opening in the top of the peaked box, BP’s Suttles said, like sand in a funnel, only upside-down.

Options under consideration included raising the box high enough that warmer water would prevent the slush from forming, or using heated water or methanol. Even as officials pondered their next move, Coast Guard Rear Adm. Mary Landry said she must continue to manage expectations.

‘‘This dome is no silver bullet to stop the leak,’’ she said.

The captain of the supply boat that carried the hulking, concrete-and-steel vault for 11 hours from the Louisiana coast last week wasn’t giving up hope.

‘‘Everybody knew this was a possibility well before we brought the dome out,’’ Capt. Demi Shaffer, of Seward, Alaska, told an AP reporter stationed with the 12-man crew of the Joe Griffin in the heart of the containment zone. ‘‘It’s an everyday occurrence when you’re drilling, with the pipeline trying to freeze up.’’

The spot where the Deepwater Horizon rig exploded and sank now teems with vessels working on containing the rogue well. There are 15 boats and large ships at or near the site — some being used in an ongoing effort to drill a relief well, considered a permanent if weeks-away fix.

Settling in to a wait-and-see mode, the vessels were making sure they were ready for the long haul. Late Saturday night, the Joe Griffin pumped roughly 84,000 gallons of fresh water into the tanks of the Ocean Intervention III, one of the vessels with the undersea robots helping in the containment effort.

News that the containment box plan, designed to siphon up to 85 percent of the leaking oil, had faltered dampened spirits in Louisiana’s coastal communities.

‘‘Everyone was hoping that that would slow it down a bit if not stop it,’’ said Shane Robichaux, of Chauvin, a 39-year-old registered nurse relaxing at his vacation camp in Cocodrie. ‘‘I’m sure they’ll keep working on it till it gets fixed, one way or another. But we were hopeful that would shut it down.’’

The original blowout was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding, according to interviews with rig workers conducted during BP PLC’s internal investigation. Deep sea oil drillers often encounter pockets of methane crystals as they dig into the earth.

As the bubble rose, it intensified and grew, breaking through various safety barriers, said Robert Bea, a University of California Berkley engineering professor and oil pipeline expert who detailed the interviews exclusively to an Associated Press reporter.