The Coast Guard ensured the safe return Tuesday morning of the passenger vessel Cetacea which became disabled about 13 miles east of Nahant, Mass., Monday afternoon. It had been due back at the dock Monday at about 4:30 p.m.

During a whale watching cruise, the 83' passenger Cetacea operated by Boston Harbor Cruises notified Coast Guard Sector Boston that it was disabled with 163 people aboard after their propeller became entangled.

Boston Harbor Cruises deployed divers aboard the Gateway Endeavor to attempt to free the propeller. Additionally, the passenger vessel Nathaniel Bowditch was directed to the scene to attempt to transfer the passengers.

The Coast Guard cutter Tybee and a 47' motor life boat crew from Coast Guard Station Gloucester was sent to the scene to assess and monitor the situation. The Coast Guard cutter Escanaba arrived later and provided medical personnel to assess the passengers and ensure their safety.

Initial attempts by the divers to clear the line from the propeller were unsuccessful. Original reports indicated a lobster pot line was caught in the propeller, but further analysis revealed it was a cable from Northeast Gateway's offshore facility which required additional dive resources and heavy duty equipment for removal.

Considering the dangers of an at-sea night operation, a passenger transfer was deemed unsafe until morning. Meanwhile, Boston Harbor Cruises provided additional water, food and blankets to the passengers.

The Tybee and Escanaba remained on scene with the Cetacea through the night and Coast Guard medical personnel remained aboard to monitor for possible medical concerns.

At about 5:20 a.m., divers aboard the vessels Bunker Hill and Scarlett Isabella freed the line from the Cetacea's propeller and the Tybee escorted the Cetacea to Boston. All passengers safely disembarked the vessel near 8 a.m., at Long Wharf near the New England Aquarium.

The cause of the incident is under investigation.