ORCAS ISLAND — An historic 133-foot schooner ran aground on rocks late Monday morning southwest of Orcas Island, and boats in the area, including two Washington State Ferries were called to help offloaded 20 people.

The U.S. Coast Guard is investigating the cause of the incident involving the 95-year-old Adventuress. The schooner ran aground while the tide was dropping in the narrow Wasp Passage, where sailors say the rocky reefs can make boating there a challenge. The incident was reported at 11:55 a.m.

Five crew members and 15 passengers were taken onto other boats, including the state ferries vessel Sealth, said Lt. Cmdr. John Park, the Coast Guard’s senior investigating officer in the region. Neither injuries nor pollution, such as a fuel spill, were reported.

The Adventuress is owned by a the Port Townsend-based nonprofit Sound Experience. The group offers educational cruises of Puget Sound and the San Juan Islands, as well as training people to sail, according to its Web site.

Park said he didn’t know the nature of Monday’s sailing trip. The Coast Guard’s preliminary investigation should be complete within a month, he said.

A diver inspected the Adventuress’ wooden hull Monday and found that its keel rested on the rocks and the hull was intact, Park said. The schooner was taken to Friday Harbor for a damage assessment, he said. Also, one of the Coast Guard’s marine inspectors was onboard the Sealth, and he spoke with people onboard the Adventuress, Park said.

Besides the Sealth, state ferries’ vessel Evergreen State, which serves the San Juan Islands inter-island route, was diverted Monday to help the Adventuress’ crew and passengers. Both ferries launched rescue boats and five passengers were evacuated from the Adventuress to the Sealth, said Hadley Greene, a state ferries spokeswoman.

The Coast Guard asked the state agency to divert the Sealth before it had finished loading for its 12:05 p.m. departure from Orcas, Greene said. The evacuation caused delays on both the inter-island and the Anacortes-San Juans routes, as well as a back-up of vehicle traffic waiting for the ferries, Green said.