Accident investigators questioned boatsmen on the island of Santorini on Monday to determine whether the crew of a cruise ship that sank in the Aegean Sea delayed evacuating more than 1,500 people on board.

Members of Santorini's boatsmen association played a key part in the April 5 rescue of the passengers -- mostly American tourists -- after the Sea Diamond foundered on submerged rocks near the island's main port.

Two French tourists are missing and feared drowned following the three-hour rescue effort during which the passengers had to scramble onto lifeboats, cross narrow gangways and climb down rope ladders to safety.

The 469-foot vessel sank about 15 hours after striking the well-marked and charted reef in fair weather.

Rescuers have repeatedly cited delays in their ability to contact the crew of the ship, which is operated by Louis Cruise Lines, part of a Cyprus-based tourism group. Many passengers also complained of being poorly informed by the crew.

Sea Diamond engineer Stelios Peroulis denied that the rescue was mishandled.

"The captain is very experienced and he followed all the necessary procedures correctly," Peroulis said Sunday.

The engineer said that after the ship hit the rocks, "the engine room flooded and I was called upstairs to prepare the life boats."

Six crew members of the Sea Diamond, including the captain and chief mate, were charged with negligence Saturday but not taken into custody, pending further testimony.

Local authorities and a contracted company were working to contain a small oil spill from the ship, which has settled on an undersea slope with most of the hull 320 feet below the surface.

The spill posed no immediate threat to the main beaches on Santorini, one of Greece's most popular vacation destinations. The ship sank in a sea-filled crater caused by a volcanic eruption 3,500 years ago.

Coast guard divers continued to probe the hull, to prepare for a search scheduled Tuesday by a remote-controlled submersible to look for signs of the two missing passengers.

Frenchman Jean-Christophe Allain, 45, and his 16-year-old daughter, Maud, were believed to be trapped in a flooded cabin in the lower decks.

Allain's wife -- who with her son survived the accident -- told authorities she had narrowly escaped from her flooded cabin located near the area where the rocks tore a hole in the side of the ship.

A total of 1,156 passengers and 391 crew were on the four-day Aegean Sea cruise, and included groups from Canada, Britain, Spain, France, Australia and the Dominican Republic. The Americans included nearly 100 students from North Carolina.