Over the past twenty years, the US oil tanker fleet, including those vessels involved in the Trans-Alaska Pipeline System (TAPS) trade in Prince William Sound (PWS), has undergone major engineering and structural improvements to comply with federal and international standards requiring that new oil tankers be constructed with double hulls, while older single hull vessels are phased out of US and international fleets.
Double hull tankers have traditionally been viewed as offering a higher level of oil spill prevention as compared to single hull construction, because the outer, double hull of the vessel can be penetrated without causing a release of cargo. Several studies have demonstrated that the rate of oil outflow from a double hull tanker involved in a grounding or hull breach is generally less than from other tanker designs. Practical experience supports these studies, as there have been a number of incidents where a double hull tanker’s outer hull has been breached, but pollution has been avoided by the containment afforded by the intact inner hull.