A U.S. Coast Guard air search for a 25-year-old Canadian woman who was swept over the side of a Nova Scotia-based tall ship off the U.S. coast was called off Saturday night as darkness set in over the mid-Atlantic.

The unidentified woman was on the Lunenburg, N.S.-based vessel the Picton Castle, which is continuing the search along with a merchant marine tanker in the area.

The Picton Castle, seen here in July of this year, was about 760 kilometres southeast of Cape Cod, Mass., when the incident took place.
(Nathan Rapheld/Associated Press)

A rogue wave washed over the ship Friday night and pulled the woman into the water about 760 kilometres southeast of Cape Cod, Mass., said Daniel Moreland, a longtime skipper of the Picton Castle.

Moreland, who's following the search from Mahone Bay, N.S., said the crew immediately threw over several pieces of rescue gear to mark the site and give the woman something to grab.

He said by all accounts she was where she should have been on the vessel, seeking shelter from the storm.

The tall ship was four days into a voyage to Grenada, travelling along the Gulf Stream, when it encountered bad weather.

The unidentified woman, described as a volunteer crew member aboard the Picton Castle, was not wearing survival gear or a life-jacket, Moreland said.

'36 hours of survival'

Earlier Saturday, a C-130 Hercules aircraft used infrared equipment to detect anything in the water, but by early evening, no one had spotted her.

U.S. Coast Guard spokeswoman Lieut. Stephanie Burns said another Hercules would return in the morning to continue looking, while the Picton Castle planned to stay at the scene and search through the night.

The coast guard estimated the woman would be able to survive about 36 hours, based on factors that include her age, her physical fitness and the water temperature of around 22 C.

"The 36-hour point should be about nine o'clock [Sunday], so if we do a first-light search in the morning that will take us through that 36-hour point," said Burns.

"At that point we'll evaluate whether or not to actually suspend or possibly keep searching."

A merchant tanker had also helped in the search, which covered more than 1,900 square kilometres.

Moreland said it was pitch black at the time, making it almost impossible for the crew of 29 to see her. Darkness was also closing in Saturday, forcing the Picton and the commercial vessel to shine lights on the water's surface.

"There's prospect for hope, but the longer it is, the worse it is," he said. "The crew is tired, but they're persevering. This is a rough go."

The woman, who has some experience on boats, was on a shelter deck in the rear of the vessel, which Moreland said is considered a safe area. It wasn't clear whether she was on watch duty at the time.

With files from the Canadian Press