Coast Guard Marine Safety Office Miami is monitoring the progress of the Isarstern, a 529-ft. tanker disabled and adrift off the coast of Marathon, Fla. The Isle of Man-flagged ship was en route Houston from Quebec, Canada when it suffered an engine casualty about 13 miles off Florida around 2 a.m. The ship has lowered its anchor to both slow its rate of drift and anchor if it drifts into shallow waters. The vessel is currently 5 miles south of Sombrero Light and 2 miles outside of the Florida Keys National Marine Sanctuary. It is slowly drifting east-northeast, parallel to the FKNMS boundary, presenting no immediate threat to the sanctuary. A commercial salvage vessel from Tampa, Fla., is on its way to rendezvous with the tanker and is expected to arrive around 7 a.m. tomorrow.