Disaster brings redundancy

The tanker Exxon Valdez will long be remembered for its grounding in Alaska, and the consequences continue to flow from that incident. In the case of Atlantic Richfield it meant moving not only to a double hull construction but also to fully redundant propulsion.

Under the US OPA 90 Act three of its current 120,000 dwt tankers have been retired from the fleet, and the company needed replacement tonnage. Similarly, under the US Jones Act, the ships had to be US-built, owned and operated, and they must be crewed by Americans. The companyÕs primary trade between Valdez and Cherry Point in Puget Sound dictates the size of the ships.

To meet its extra requirements of a 30-year fatigue life the company looked at a number of different ships, including North Sea shuttle tankers. Its latest tonnage, with the exception of dynamic positioning and buoy or turret loading, reflects this aspect.

But it is the propulsion arrangement that will intrigue many. The ships, which are under construction at Avondale, feature twin, fully redundant engine arrangements. Each of the engines is located in its own engine room, which are separated by a continuous bulkhead from the keel to the upper deck. The ships are also fitted with twin rudders and a bow thruster