Double hull ship
A double-hulled ship , also known as a double-hulled ship, is a ship with a redundantly constructed outer hull . The main reason for the construction of double-hulled ships is the higher security in the event of a collision or a grounding.
Double-hulled ships are constructed in such a way that, in addition to the outer skin and the longitudinal and cross bracing, they have additional bulkheads and decks that form a complete second hull. Should the outer skin of the ship be damaged by a marine accident, the second hull is intended to prevent larger parts of the ship from filling up or the cargo from escaping.
Starting with the Great Eastern , which can be considered the first double-hulled steamer in the world and was decades ahead of its time in 1858, the development steps towards the double-hulled ship were not initially direct safety developments, but were made for economic reasons. The first step was originally to build ships with double bottoms . This was used to be able to absorb ballast water . Later, double-walled tankers were built for the transport of hot goods such as bitumen , molasses or paraffin . Here, the double shell offered an improvement in thermal insulation and thus fuel savings.
After repeated tanker accidents, the stranding of the Exxon Valdez in 1989 gave the final impetus for the introduction of double-hulled tankers. The United States of America first passed the Oil Pollution Act (OPA 90) in 1990 , which prescribes double hulls for new oil tankers and, according to age limits, also for existing ships. The International Maritime Organization (IMO) decided in 1992 in the International Convention for the Prevention of Pollution from Ships (MARPOL) that worldwide all tankers of a certain size and above that were delivered from July 1996 onwards had to have a double hull. After the Erika sank in 1999, the IMO expanded the 2001 decision to the effect that from 2015 only double-hull tankers may be operated. Since July 1, 2006, the double-hull construction has also been required for the construction of bulk carriers.
As a ballast tank, the double hull has also established itself in the construction of other types of ships, such as container ships . The use of the double hull as a ballast tank is one of the dangers of the concept. Filling with seawater means that the inner walls of the tanks are very susceptible to corrosion, which makes regular checks and protective coatings necessary.