A ferry that sank with 454 people on board was carrying heavy cargo that may have shifted in heavy waves, causing the ship to tilt and then sink, the chief investigator said Sunday.

Seventeen more people were rescued Sunday after spending more than a day in chilly, storm-whipped waters, bringing the number of survivors to at least 311, officials said. At least 39 people were dead.Rough weather continued to hamper rescue operations. A navy ship was forced to turn back Sunday before reaching the accident area because of powerful waves.

The large Princess of the Orient sank during a tropical storm Friday night. Maritime officials said several other ships had also reported difficulties during the storm, and passengers in other boats had been injured.

But they said the Princess of the Orient - one of the Philippines' largest inter-island ferries with a capacity of 3,900 passengers - should have been able to withstand much worse weather. Survivors said the ship sank in less than an hour.

Chief accident investigator Arnie Santiago said the ship was carrying 15 vehicles and 66 containers of truck parts and other heavy materials that may not have been properly secured.

"The way the ship tilted indicates that the cargo moved," he told the Associated Press.

He said some of the ship's water seals also may have been damaged by a fire in 1997. Carlos Go, chief executive officer of Sulpicio Lines, owner of the 24-year-old ship, said the ferry was seaworthy despite the fire.

A crew member, Vincente Go, said the ship began listing to the left and did not stabilize even after the crew began pumping ballast water to the right side.

Sulpicio Lines also owned the Dona Paz, a ferry that collided with a tanker in 1987, killing 4,341 people in the world's worst peacetime shipping disaster. A year later, 250 people died in the sinking of another ship owned by the company, the Dona Marilyn.

For a second day, anguishedrelatives waited at a pier in Manila for the return of rescue ships. Many burst into tears as a navy patrol craft arrived with 13 bodies, including two children, bloated from decomposition and covered with flies.

"I hope my sister isn't one of them," sighed Praxedes Coronas as she stared at the pile of bodies. "We've been sleepless since yesterday, not being able to confirm whether she's dead or alive."

Lydia Maranan also waited for word of a sister. "It's painful," she said, pounding her chest. "But we'll wait until she turns up. We want to take her home."

The company said there were 352 passengers and 102 crew aboard, revising earlier figures to account for people not listed in the manifest, the coast guard said. No foreigners were reported on board.