CHEVRON SHIPPING ACCENTS MIDSIZE TANKERS

Chevron Shipping Co. expects soon to take delivery of the second crude oil tanker in a construction series focused on midsize vessels.

The series took shape early in 1989, when Chevron let contract to Ishikawajima-Harima Heavy Industries Company Ltd. (IHI) of Japan for construction of four 150,000 dwt tankers at a cost of about $42 million each.

By the time the John Young, first of the 150s or million barrel tankers, was delivered last summer, its value had increased to about $60 million, Chevron Shipping parent Chevron Corp. reported in Chevron World, a corporate publication.

IHI built the John Young in Japan, but Ishibras, an IHI affiliate in Rio de Janeiro, is building the next three. It will deliver two this year-the J. Dennis Bonney in May and the Bruce Smart in October-and one, as yet unnamed, in April 1992. Chevron vessels are named for board members chosen by Chairman Ken Derr.

In addition, Chevron has let contract for two 130,000 dwt tankers, also to be built by Ishibras. Those will join the company's fleet in December 1992 and June 1993. Thereafter, Chevron estimates it will buy two 150,000 dwt vessels/year for 6 years.

But the number of tankers in the Chevron fleet will stay at about 40-45 for the next several years as the company disposes of older vessels.

MIDSIZE ACCENT

"We have a growing need for midsize tankers," Chevron Shipping Pres. Doug Wolcott told Chevron World.

Here's why:

With a runup in crude oil prices in the 1970s, exploration and production activity increased, and several large fields went on stream around the world. This allowed crude oil buyers to diversify their sources, relying less on Middle East supplies.

The once popular supertankers-those larger than 160,000 dwt-began to go out of favor.

In 1980, Chevron trimmed four of its tankers to 150,000 dwt from 212,000 dwt by removing their midsections-much like taking out the center leaf from a dining table. The four newest vessels are replacements for the down-sized ships, two of which have been sold.

At about 900 ft in length, the 150s can moor safely at the company's El Segundo, Calif., refinery where 1,000 ft is the length limit. They also can berth at the Richmond, Calif., wharf, where regulations restrict vessels of greater tonnage.

With a draft of 55 ft, they can maneuver in water shallower than larger vessels re quire-at Dumai, for example, in Sumatra.

Although not precluded from Middle East trade, the 150s were designed for Chevron's growing trade between Indonesia and the U.S. West Coast.

The 130s generally will sail the West Africa-U.S. East Coast route.

"We buy a lot of Alaskan North Slope oil that's delivered in the seller's ships," Jack Leutwyler, Chevron Shipping vice-president of traffic and chartering, told Chevron World. "But since North Slope production is tapering off, we'll eventually have to buy oil elsewhere and bring it to the West Coast in our own ships. We'll need more 150s."

VESSEL DESIGN

It's not just their accommodating size that makes the new vessels attractive, Chevron said. They also have streamlined bows and sterns for better propulsion and low speed diesel engines that cut fuel consumption by about one-third without sacrificing speed.

The vessels also are equipped with the latest navigation aids, including satellite communications, two radar collision avoidance systems, a Loran or long range navigation system that uses radio signals to determine vessel position, and a computerized monitor that continuously checks 250 functions in the engine room.

Capt. Giancarlo Allara, Chevron Shipping safety superintendent, cited the vessels' inert gas system as one of their most important safety features.

The system transforms boiler exhaust into inert gas. Empty spaces in cargo tanks are filled with the gas to prevent the buildup of an explosive mixture of combustible vapors and oxygen. Although international rules say the gas can be 8% oxygen,

Chevron set a limit of 5%.

SINGLE HULL, DOUBLE HULL

Perhaps the greatest controversy in the tanker industry recently has focused on double hulls, Chevron pointed out.

Since Exxon Corp.'s 1989 oil spill off Alaska, the U.S. Congress has heard arguments for and against this type of vessel design. In 1990, Congress adopted legislation requiring a gradual phase-in of double hull tankers for trade in U.S. waters.

Chevron's new 150s, ordered before the Exxon Valdez spill, will have single hulls. The 130s, however, were caught in the middle of the single hull/double hull debate. They first were designed as single hull ships but then changed to comply with the new law even though they were ordered before the double hull requirement went into effect.

"Double hulls don't guarantee safety," Wolcott said. "in fact, some double hull designs might create hazards."

If only the outer hull were punctured, for example, flooding of the double hull space could under certain circumstances, cause instability. This flooding also could cause the ship to lose buoyancy and sink deeper than a single hull vessel would.

In addition, if vapor from a cargo tank leaks into the space between the hulls, there is a potential for an explosion. "Because we weren't satisfied with current designs," said Wolcott, "we came up with a new one."

The critical aspect of the design is how the space between the hulls is divided into compartments. On Chevron's 130,000 dwt tankers, four strategically positioned side tanks provide buoyancy even if the other tanks are flooded. The vessels are designed to withstand damage to virtually the entire length of the ship.

While the usual distance between hulls is 2 m, the Chevron design allows 3.3 m to make maintenance and safety inspections easier. In addition, the company insisted on a vapor purging and air circulation system between the hulls.