A woman killed when a mast snapped and toppled onto the deck of a historic sailing vessel that carries tourists off the Maine coast was a physician at the hospital where three other victims were taken for treatment, officials said Tuesday.

Dr. Emily Mecklenburg, 40, of Rockland, was declared dead Monday after she was evacuated from the stricken vessel Grace Bailey by the Coast Guard, Nicole Jacques, a spokesperson for owners of the schooner, said Tuesday. Three others who were injured were taken to PenBay Medical Center in Rockport where Mecklenburg worked, officials said.

The Coast Guard is investigating why the schooner's main mast snapped in conditions that were not windy. The schooner was about 1 mile east of Rockland harbor, the Coast Guard said.

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There's no timeline for the investigation, which could take weeks or months.

"We want to make sure the investigation is being done thoroughly and that the necessary boxes are being checked," Ensign Matthew Bartnick, a Coast Guard spokesperson in Maine, said Tuesday.

The Grace Bailey was part of Maine's windjammer fleet comprised mostly of large historic sailboats that take tourists on multi-day outings. The Grace Bailey was returning from a four-day excursion when the mast snapped late Monday morning.

An emergency medical technician who assisted said that one person was briefly trapped under the fallen mast. Three others suffered head and back injuries, he said.

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While the Grace Bailey was old, built in 1882, there are several older vessels that carry passengers off the Maine coast. The Lewis R. French and Stephen Taber were both built in 1871, Jacques said.

All of those vessels have been refurbished multiple times over the years, and most of the planks and other components have been replaced, Jacques said. The mast that splintered was not Grace Bailey's original mast, she said.

The Grace Bailey, which was carrying 33 passengers and crew, was formerly known as the Mattie before coming under new ownership and being renamed in the past year. One of the new owners is actor Marc Evan Jackson, who is known for his roles on TV shows "Brooklyn Nine-Nine," "Parks and Recreation" and "The Good Place."

Jackson used to sail on windjammers as a young man and comes back year after year to sail in Maine, Jacques said. He decided to become a part owner when the opportunity presented itself, she said.