BOOTHBAY – A spectacular fire Friday destroyed a commercial boatyard that specialized in tugboats, reducing the wooden harborside structure to ashes and twisted metal.

The 50,000-square-foot building at Washburn & Doughty Associates was rocked by a series of explosions as flames ripped through the facility. There were no reports of injuries, but one firefighter was treated at the scene for heat exhaustion.

“I’ll tell you, it was some hot. The heat was unbelievable,” said Scott Carpenter, who works for a crane company contracted by the shipyard. Like the 100 boatyard employees, Carpenter got out with his life as flames raced through the structure.

In addition to the main boat-assembly building, the office, shed and storage buildings were destroyed, Chief Tim Pellerin of the Lincoln County Emergency Management Agency said. Speaking to reporters in Portland, Gov. John Baldacci put the property damage at $30 million.

The boat builder in East Boothbay serves as a year-round economic linchpin in an area that’s heavily dependent on summer tourism.

“Hopefully, they’ll rebuild,” said Ed Shaw, who worked at the shipyard off and on before his retirement. “The industry needs them.” His wife, Betty, said the village had lost a treasured piece of history in addition to a major employer.

The blaze sent a plume of black smoke skyward, and about 200 homes and businesses near the boatyard were evacuated as fire crews and ambulances from two dozen towns in four counties converged on the scene. Specialists in hazardous materials were also called in.

The Coast Guard said its station in Boothbay Harbor provided a 47-foot motor lifeboat to transport firefighters around the boatyard so they could get to areas they otherwise couldn’t reach. In addition, a 25-foot Coast Guard response boat enforced a safety zone around the boatyard to keep mariners away from the fire scene.

Two tugboats were under construction in the building that was leveled. Another vessel that was in the water outside the boatyard was saved.

Investigators from the State Fire Marshal’s Office concluded that the blaze started near one of the tugboats that was under construction in the building, but they haven’t yet determined the cause, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

Investigators will be back at the boatyard Monday to interview workers to determine the sequence of events leading to the fire, McCausland said.

The boatyard’s operations manager, Lee Smith, said the company’s first priority is to launch the nearly completed tug within the next couple of weeks.

Smith, who was in the pilothouse of the new tug when the fire broke out, said workers will cooperate with the fire marshal’s office, and there will be an internal investigation.

In the meantime, employees are being asked to show up at the boatyard at 7:30 a.m. Monday to discuss a transition plan that is to be drawn up over the weekend.

“This is going to be a rebuild operation,” said Smith.

The fire broke out just days before the company was to begin a $5 million expansion, said Smith. While specializing in tugs, Washburn & Doughty has also built passenger vessels, fishing boats, barges, ferries and research vessels.

The intense fire started around 9:30 a.m., and black smoke could be seen from the bridge linking Wiscasset and Edgecomb, about 10 miles away.

“I’ve never seen smoke like that,” said Kristina Ford, who lives near the boatyard. The fire, she said, was “just obviously unstoppable. It was just so huge.”

Ron Riml, a retired police officer, showed pictures of flames shooting 30 feet above the roof as he watched from the top floor of his house several hundred yards away. The scene was “almost like the Hindenburg as the frame and everything went up in flames,” he said.

“It went quickly, and once it went quickly there were a lot of explosions,” Riml said.

Baldacci phoned Smith at the scene to discuss the damages, and was briefed on the fire by the Maine Emergency Management Agency. He pledged to provide whatever state support is needed to help the company and the community recover.

Response teams from the Department of Environmental Protection and the Department of Labor were activated and the Department of Economic and Community Development was prepared to help.

“The state stands ready to provide whatever support is needed to fight this fire, and to help Washburn & Doughty and the community recover,” the governor said earlier from Augusta.

Sen. Olympia Snowe, R-Maine, called the fire and the devastation it caused “distressing and untimely. My thoughts are with the employees of this family-owned shipbuilding company and the community that surrounds it. I offer my full support of the workers and families whose livelihoods will be affected by this tragic event.”

Snowe added that members of her staff “will be at Monday’s Rapid Response session to provide any and all resources and support to help rebuild and restore this critical shipbuilding facility.”

Sen. Susan Collins, R-Maine, said she was “saddened to learn about the loss of this facility and the many workers and their families who will be hurt by this devastating event. My office has been in touch with the Lincoln County Emergency Management Agency and … the town manager to offer assistance. We have also contacted the U.S. Department of Labor to notify them about the large number of employees whose jobs will be affected.”

Democratic Rep. Tom Allen of the 1st District said he was “grateful to the first responders from the many municipalities who responded in a timely fashion to the fire. … Their rapid response resulted in the safe evacuation of all of the 85 employees of the company. I stand committed to working with Gov. Baldacci and the congressional delegation to assist the company and its work force in recovering from this tragic event.”

In early 2007, Washburn & Doughty considered expanding its business to a site in Bucksport but later backed away in favor of a parcel in Harpswell.