Until the nineties, most oil tankers had a simple single hull construction. In order to better protect the environment, particularly in the event of low impact collisions/groundings, legislation was passed in 1993 to accelerate and regulate the phasing out of single hull oil tankers, which must cease trading or be modified to double hull construction by end 2010. Existing vessels with single sides but double bottom will be allowed to trade until 2015. While these cut-off dates have been agreed worldwide, trading of single hull vessels is already becoming more difficult as some major oil companies and charterers have adopted a double-hull only policy. There is, however, an exemption in the legislation that allows for continued trading of single-hull vessels if both the vessel's flag state authority and the port authority where it is trading agree to accept it.
In a double hull tanker the cargo spaces are protected from the environment by double side and double bottom spaces dedicated to the carriage of ballast water. These extend for the full length of the cargo carrying area. Internal piping is routed so that only water carrying pipes pass through the ballast areas so that ballast water cannot accidentally be contaminated by any leakage in the cargo piping system.
On 1 April 2006 new international shipbuilding standards were introduced, intended to ensure stronger, safer ships. The Common Structural Rules (CSRs) stipulate new structural requirements relating to fatigue, material strength and corrosion which are designed to ensure a longer, safer life for vessels.
Today South Korea, Japan and China have the greatest shipbuilding capacity. Together they account for more than 90% of tanker construction capability. South Korea and Japan both have 14 docks for building VLCCs. China has eight and has already started an aggressive expansion plan.
A VLCC takes between 5.5 and 7 months to build. In early 2006, shipyards were quoting US$120 million to build a standard specification VLCC, but the new CSRs imposed in April 2006 may further increase prices.