New Standard Set with Double-hulled Double-screw Tankers

New Standard Set with Double-hulled Double-screw Tankers

Two new tankers on order to carry North Slope Crude from Valdez to the West Coast meet the Oil Pollution Act of 1990 requirements that older tankers be phased out and replaced with double-hulled vessels, meet or exceed state, federal, and international safety requirements and are designed to improve redundancy maneuverability and self-sufficiency.

Specially designed ships represent new generation of vessels

Each ship will carry 1,017,000 barrels. The contract for the ships was signed July 1, 1997 by Arco, and construction began in December. The two-ship contract carried a $332 million price tag.

The capacity of the two tankers will be equivalent to about 200,000 barrels a day of production.

Redundancy, Maneuverability
This is the first ship that’s been built with twin separate engine rooms. There’s a fire bulkhead between the two engine rooms, which also serves against flooding, so that if power is lost in one room, the other will remain unaffected. The two systems are completely independent of one another.

With twin engines, the ship also has two propellers and two rudders. The rudders turn up to 45 degrees; present rudders only turn about 35 degrees. This enables the ship to turn within its own length and spin around at slow speeds.

Enclosed Bridge, Joystick Control
The new tankers will have a fully enclosed bridge, with windows from one side to the other, improving visibility and protecting the electronics.

A single joystick will control both rudders, both propellers and the bow thruster. The ship has multiple levels of control systems so that if in the event the joystick fails it is backed up by two similar joysticks that separate port and starboard. After that, it’s backed up by individual controls on both the throttles and the rudders for each side and each engine. Each engine room can be operated separately or jointly.

Engine Rood Designed for Unmanned Watch
State-of-the-art automation will be used in both cargo control and the engine rooms. The cargo control room has normally been on the upper deck where visibility of the deck is restricted. The cargo room has been moved up a deck in the new tankers. For the first time, the cargo control system can be operated from the bridge of the ship, minimizing the need for turning out a crew to operate the system.

A new power management system means the engine rooms can be unmanned, automatically sensing increasing loads from heavy seas. It will reduce the pitch on the propellers, maintaining a constant power on the engines, which enables the ship to run more efficiently with less damage.

Winch Controls to the Rail
Winch controls, used in docking the ship, are ow placed so that a spotter is needed to tell the winch operator when the lines were getting tight.

Bits, used to tie up to the tanker, will be recessed in the sides of the ship so that tug crews can put their own lines on and take them off without crew on deck handling the lines, eliminating the risk of crew injuries.

30-year Life, Serviceability
The new tankers will have a 30-year fatigue life, using sophisticated computer techniques to perform a finite element analysis, and design to strengthen weaknesses. In order to increase serviceability, most equipment is accessible up front, making changes to electronic equipment faster and easier.

Positioning Check Within 15 Feet
Global positioning capabilities that will allow crews to check their position within 15 feet. It will also have a warning system linked to the radar that will acknowledge to the crew that the vessel is off course with just a slight deviation from course.

A New Standard in PWS Tankers
John Devens, executive director, Prince William Sound Regional Citizens’ Advisory Council, called the announcement of the new tankers “an exciting day for all of us who are interested in safe transportation of crude oil through Prince William Sound and associated waters.”

Editor’s note: This article, by Petroleum News Alaska was edited for length.