BOSTON (AP) – Authorities intensified cleanup efforts Thursday as oil from a 15,000-gallon spill in Buzzards Bay continued to wash ashore in large patches and as tar balls.

Meanwhile, open water skimming was hampered by 10- to 15-knot winds that made the oil more difficult to retrieve, the Coast Guard said.

Any cleanup of Buzzards Bay is difficult because choppy waters and sudden wind changes make the oil’s movement unpredictable, moving it into the bay’s nooks and crannies, said Gene Cookson, president of Clean Harbors Inc.

“Buzzards Bay is relentless,” said Cookson, whose company was hired to remove the oil by Bouchard Transportation Inc., which owns the barge that spilled the oil.

The Coast Guard said Thursday that shoreline crews were increased from about 160 to 213, most of them Clean Harbors workers. Cookson said Clean Harbors’ crew would probably be up to 250 by Friday.

About 2,000 gallons of oil had been recovered by midday Thursday.

Although high-tech equipment exists for dealing with spills, cleanup often comes down to little more than basic scooping, pumping and digging, said Michel Boufadel, a Temple University expert on oil spill remediation. Speed is especially important because time allows oil and water to mix. That increases the mass of the spill.

“Removing seriously hazardous material is like a cancer extraction. You don’t want to play. You want to take it out as fast as you can,” said Boufadel, who said the oil recovery seems to be moving along slowly.

Cookson disagreed, saying efforts are moving as quickly as possible given the conditions.

“I believe it’s going as well as can be expected,” said Petty Officer Linda O’Brien, a Coast Guard spokeswoman.

Bouchard hired three private companies – Clean Harbors, Marine Spill Response Corp. and Fleet Environmental Inc. – to clean up the oil, according to company spokeswoman Suzanne Tavani. Between them, they had seven skimmers at work on the spill Thursday, she said.

Several different types of skimmers are used, depending on water and oil conditions.

, said Scott Linsky of the Coast Guard Atlantic Strike Team. One skimmer, resembling a large doughnut, is dragged through the oil sheen between two vessels, he said.

The skimmer sucks oil and water through inlets while the operator tries to keep the pump as close to the point where the oil and water meet, ensuring the maximum amount of oil is gathered.

Another skimmer, used with thicker fuels, resembles a conveyor belt and is coated with a substance that attracts oil, Linsky said. The belt moves the oil past a blade that scrapes the fuel off. A similar skimmer used in tighter areas is a round drum that rotates past a blade.

Clean Harbors has used two “V-Nose” skimmers, effective with heavy fuel like that spilled in Buzzards Bay, Cookson said. The boats push a V-shaped basin in the front of the vessel to gather the oil.

With many skimmers, collected oil is pumped into storage tanks, which range in size from 1,000 to 30,000 gallons, Linsky said.

Skimming is extremely difficult on rough seas because the oil is harder to collect and pumps work inefficiently. When the weather is bad, the focus turns to shoreline cleanup, he said.

Snares shaped like a cheerleader’s pompom and covered with oil-attracting material can be placed at the low tide line to soak up oil as it comes in. But shoreline cleanup mainly involves digging and raking, Cookson said.

Gov. Mitt Romney, visiting cleanup efforts at a beach in Dartmouth Thursday, said the spill may have been preventable. The barge – though legal – was single-hulled, not double-hulled.

“That makes us particularly angry and we’re going to exercise every option we have to ensure that the responsible parties are made to pay to the extent that they can,” Romney said.

The spill is under investigation by the Coast Guard, which has performed drug tests on the crew. The Coast Guard on Thursday declined to discuss the investigation.

Officials believe the boat may have run aground on an underwater ledge near the entrance of the bay, though the barge didn’t stop for another 10 miles. The Coast Guard has said the crew followed proper procedures for reporting the spill.

AP-ES-05-01-03 2151EDT