The jagged reef that ripped open the wandering Exxon Valdez and dirtied Prince William Sound also reopened the debate on requiring a second layer of steel as an added safety factor on supertanker bottoms.

"This spill raises a red flag we may not have sufficiently stringent design requirements," said Clifton Curtis, president of the Oceanic Society, based in Washington, D.C."It's a world-class catastrophe, a benchmark for the worst-case spill ever," Curtis said. "It does call again for re-examination of tanker design. There's lots of support to require double bottoms."

A double bottom is a second skin covering a ship's underbelly. It creates several feet of insurance space that must be penetrated before cargo holds leak.

But it would have also reduced the capacity of the Exxon Valdez and added an extra 10-15 percent to the $125 million cost of the tanker, launched with a single hull in 1986 in full compliance with U.S. and international law.

Industry analysts argue that double bottoms work if a ship runs aground on a softer sandy bottom but are ineffective against treacherous outcrops such as Bligh Reef. The extra bottom, when breached, can also fill with seawater and cause a tanker to capsize and break apart.

"Double bottoms are not the cure-all people think. It possibly could lead to a worse spill," said Sean Connaughton of the American Petroleum Institute.

"You can have the best designed ship, with the most modern equipment and best trained crew in the world, and you can still have accidents like this," he said. "If you want to get rid of the problem of oil tankers, don't ever use any oil."

The force of the Good Friday accident would not have kept the Exxon Valdez from hemorrhaging oil even if it had a double bottom.

The ship, longer than three football fields, cruised through the calm night on a routine run carrying 52 million gallons of oil. A 31,650-horsepower engine pushed it at 15 miles an hour.

It had magnetic and gyroscopic compasses, an electronic direction finder, two radar systems, a satellite navigation system and two steering systems that work independently in case one fails - everything necessary to keep a proper course.

But its captain, Joseph Hazelwood, who had lost his privilege to drive cars on land because of two drunken driving convictions, had too much liquor in his blood and was in his private cabin.

In the hands of an unqualified third mate, the supertanker strayed more than a mile out of shipping lanes and rammed an undersea mountain.

Holes as wide as 20 feet rent eight cargo holds. But even if a double bottom were mandatory, the damage would have penetrated the 6 feet of space required for the Exxon Valdez, officials said.

In 1977, President Carter advocated double bottoms for supertankers but was willing to accept alternative ways to limit oil pollution.

The next year, a compromise with international shippers kept the extra bottom from becoming U.S. law. The Intergovernmental Marine Organization, a U.N. agency based in London, adopted segregated ballast as a safety feature that would reduce the incidence of oil slicks.

The ballast tanks, empty when a ship is fully loaded, carry water when it is empty. This ended the practice of filling cargo tanks with water for ballast and then flushing the gloppy residue into the ocean. The segregated tanks, which are placed around a tanker's sides, serve as cushions in case of collision.

The side tanks were desired because accidents were 1.5 times more likely to damage a ship's side than its bottom, according to Coast Guard studies. Side damage came from collisions with other ships, which often resulted in fires and explosions.

What's more, a National Academy of Sciences study in 1973 said 80 percent of oil pollution came from operational practices such as flushing tankers with sea water. Accidents made more headlines but did only 20 percent of the environmental damage.