The Navy was to have tried a fourth time this morning to refloat the USS Port Royal, the warship that ran aground about a half-mile off Honolulu International Airport's reef runway on Thursday.

At 4 a.m., during the high tide, tugboats were again to try to dislodge the guided missile cruiser stranded in 17 to 22 feet of water.

The Navy planned to remove the ship's anchor and anchor chain, which weigh about 40 tons, and drain the ship of 800 tons of ballast seawater, said Rear Adm. Joseph A. Walsh, deputy commander and chief of staff of the U.S. Pacific Fleet.

If that doesn't work, the Navy will consider dredging a channel behind the 9,600-ton, 567-foot warship, which is stuck in sand on the rocky bottom.

Previous attempts on Friday and Saturday to dislodge the ship were unsuccessful.

When the Navy tried again early yesterday, it used a salvage ship, a motor vessel and four Navy and three commercial tugboats.

"Although we had more horsepower, we were unable to pull the ship free," Walsh said. "We were only able to pivot the ship about 20 degrees.

"Our priorities have been, and remain, the safety of the crew, the safety of the ship and the safety of the environment," Walsh said. "There have been no injuries associated with the grounding or our recovery efforts."

The $1 billion USS Port Royal left port on Thursday for sea trials. The cruiser had been in drydock for routine maintenance until about a month ago.

The Navy is investigating the cause of the grounding and would not discuss any details of its investigation. The cost of removing the ship has not been determined, Walsh said.

If the Navy is unable to move the Port Royal today, it will consider removing the fuel and more weight, Walsh said. The Navy planned to remove fuel before yesterday's attempt, but heaving seas prevented that, Walsh said.

The Port Royal is homeported at Pearl Harbor and was commissioned in 1994.

The ship's hull is sound and there have been no fuel leaks or spills, the Navy said.

"We are working closely with both the U.S. Coast Guard and the state of Hawai'i to ensure all precautions are being taken should a release of fuel occur," Walsh said.