Over the objections of the United States, the International Maritime Organization endorsed yesterday mid-deck oil tankers as an environmentally acceptable alternative to the double-hull tankers required under U.S. law.
The mid-deck design involves dividing a tanker's cargo space into upper and lower holds. Backers of the mid-deck design maintain that, in serious accidents, mid-deck ships would spill less oil into the environment than double hulls.
Although the IMO decision was a disappointment to environmentalists and other proponents of double-hull tankers, they said they expected double hulls to remain the international standard for the construction of oil tankers.
Since mid-decks remain illegal in U.S. waters, ship owners are unlikely to build ships that could operate only in certain world markets.
"I don't think we'll see these ships," said Sally Ann Lentz, a staff attorney for Friends of the Earth in Washington. "No ship builder in his right mind will build one if he's limited where he can take it."
Rep. Dean Gallo, D-N.J., who sponsored the provisions of U.S. law that require ship owners to gradually convert their fleets to double-hull tankers, said he also thought all new tankers would be built with double hulls despite the decision.
The International Maritime Organization is the marine safety arm of the United Nations. The standards established by the organization for ship design apply to all the nations that belong to the organization, including the United States.
However, nations that formally oppose new standards at the time they are adopted are not bound to follow them, Ms. Lentz explained. "This puts us in a good position to reject anything but double-hull tankers in our waters," she said.
No mid-deck tanker has even been built, but ship operators and foreign shipyards have been pressing for their acceptance.
Mid-deck ships have double skins on their sides but only single skins on their bottoms. In theory, if the bottom of a mid-deck tanker were punctured, pressure differentials would prevent most of the oil from escaping into the environment.
Critics have argued that mid-decks would still leak some oil whenever the bottoms were punctured, while double hulls would leak oil only in an accident severe enough to rip open both the outer and inner hulls.