The Navy says in a statement that those aboard blamed high winds and rough seas for the capsizing Thursday evening.
The boat was owned by West Island College International, based in Nova Scotia.
A spokesman there confirmed the incident but declined to give details.
The school's Web site says it gives high school and college students the chance to study while sailing the world.
The ship had left Brazil's northeast on Feb. 8 and was expected to dock in Montevideo, Uruguay, on Tuesday.
