Ocean Classroom Foundation, a Damariscotta-based organization that offers schooling at sea, is shutting down in a month.

The foundation’s debt “simply became unsustainable” due to the cost of repairing two of its three schooners, Greg Belanger, the executive director, said Friday.

The organization has offered a range of schooner-based educational programs, from weeklong “seafaring camps” to semesters-at-sea that take students from the Canadian Maritimes to the Caribbean during three-month voyages. As the students learned sailing skills on one of the foundation’s schooners, they also learned about the ocean ecosystem and continued to take classes from a traditional school curriculum.

“It is with deep regret that we conclude this voyage,” Peter Neill, the foundation’s chairman, said in a release announcing the decision.

Belanger said the foundation sought to consolidate its debt in 2010 by taking out a $2.2 million mortgage. But this year, it was hit with the prospect of major bills to repair the Westward, a steel-hulled schooner built in 1961, and the Spirit of Massachusetts, a wooden schooner built in 1984, both of which are currently in Portland.

He said the ships each need at least $700,000 for major overhauls and even the Harvey Gamage, a wooden schooner built in 1973 that is still operating and will be used for programs through Aug. 31, needs about $100,000 of work, scheduled to be done in Portland this fall. In a few years, he said, the Gamage, too, would need a major overhaul.

“We had to accept the reality that funding our debt, while fixing these boats, is unsustainable,” Belanger said.

“The older the vessel gets, the more frequent the need for major repairs,” he said. “Our ships need more capital investment than we can raise.”

Belanger said wooden schooners need a major overhaul every 10 to 15 years. He said steel ships may be able to go a bit longer between major work, but they can be more expensive to repair because removing and refitting steel plates, which have to be welded into place, can be costlier than replacing wooden planks.

Belanger said the foundation will work with its lender to figure out what to do with the schooners. In addition to having two of the vessels laid up for major work, the foundation will be facing a buyer’s market for schooners.

For instance, the Virginia Maritime Heritage Foundation announced Friday that its 126-foot wooden schooner Virginia is up for sale. An official for the foundation told The Associated Press that the cost of operating the ship, which was built in 2005, is more than the organization raises through sailing education programs and fundraising.

The 92-foot wooden Spirit of South Carolina, which was used for education programs and as a tourist attraction by the South Carolina Maritime Foundation, was appraised at $2.2 million and then sold earlier this year for $950,000.

“There is no formal plan today about what will happen with our three vessels,” Belanger said. “I expect that by September, there will be a plan.”

Belanger said the foundation had about six administrative staffers. Three of them, who had been scheduled to return to graduate school this fall, will instead be let go. He and two other staffers will stay through August to oversee programs for about 110 students that month. The 12 foundation employees aboard the Harvey Gamage will stay on to run those shipboard programs and they will be let go when the foundation ceases operations Aug. 31, he said.