A generic term for a vessel which carries large quantities of any material in bulk, but is now generally used to describe a large merchant vessel developed during the 1950s to transport large volumes of unpacked commodities such as oil (see tanker), bauxite, coal, grains in bulk, phosphate, nitrate, and iron ore. Oil/ore carriers are designed to carry both commodities. OBO (oil/bulk/ore) carriers, more complicated to build and more expensive, but potentially more profitable, can switch between different cargoes. All are now constructed with bulbous bows and nearly all have the bridge, engines, and accommodation placed aft. OBOs make up such a large proportion of the 5,500 bulk carriers operating worldwide that they are now considered as a separate category of the world's shipping. All such carriers face the problems of cargo movement and cargo self-ignition. They must allow for the carriage of high-density cargoes which will bring the ship down to its load line while leaving much of the hold space empty.
Building such large vessels with their huge holds brought with it serious problems, and by the 1980s the loss of bulk carriers had reached worrying proportions. No less than 151 OBOs were lost between September 1980 and August 1987, including the Derbyshire, 38 of them having foundered at sea, sometimes with heavy loss of life. Between 1990 and May 1997 99 bulk carriers sank at sea with the loss of 654 lives.
Structural failure has certainly been the cause of some of these incidents. Along with all merchant ships, bulk carriers are designed and built to standards laid down by various classification societies. But because of the corrosive nature of some of their cargoes, OBOs are particularly vulnerable to rust and can deteriorate quickly if the hull is not rigorously maintained. This, combined with using some flags of convenience to cut costs, the huge tonnage of cargo carried, and the necessity for masters sometimes to maintain a high speed in adverse weather conditions to keep to their schedule, all add up to an intolerable stress on a bulk carrier's hull if it is past its prime.
A study by the International Association of Classification Societies found that, if flooding occurred for any reason in the foremost hold, the bulkhead between it and the adjacent hold was liable to collapse, leading to a domino effect which eventually sank the vessel. This led the Maritime Safety Committee of the International Maritime Organization to bring in stricter regulations for both existing and new bulk carriers, and in December 2002 it adopted amendments to Chapter XII of the International Convention for the Safety of Life at Sea (SOLAS) to include additional safety measures for them.
Subjects: Maritime History.