[7] The second method required the shipper to charter an entire ship and spend time and money to build plywood bins into the holds.

[9][10] Before World War II, the international shipping demand for bulk products was low—about 25 million tons for metal ores[12][13]—and most of this trade was coastal.

[14] However, on the Great Lakes, bulk carriers hauled vast amounts of iron ore from Minnesota and Michigan's northern mines to the steel mills.

In 1929, 73 million tons of iron ore was transported on the Lakes, and an almost equal amount of coal, limestone, and other products were also moved.

[15] Two defining characteristics of bulk carriers were already emerging: the double bottom, which was adopted in 1890,[9] and the triangular structure of the ballast tanks, which was introduced in 1905.

[9] After World War II, an international bulk trade began to develop among industrialized nations, particularly between the European countries, the United States and Japan.

[13][16] In this period, Great Lakes freighters increased in size, to maximize economies of scale, and self-unloaders became more common to cut turnaround time.

[17] Bulk carriers are segregated into six major size categories: small, handysize, handymax, panamax, capesize, and very large.

[42] In terms of the number of bulk carriers registered, the top five flag states also include Hong Kong with 492 ships, Malta (435), Cyprus (373), and China (371).

[44] The Fednav Group in Canada operates a fleet of over 80 bulk carriers, including two designed to work in Arctic ice.

[4] South Korea, with notable shipyards Daewoo and Hyundai Heavy Industries,[4] ranked second among builders, with 643 ships.

The bulk freight market is very volatile, with the type of cargo, size of the vessel, and the route traveled all affecting the final price.

[54] This is often done by 'beaching' the ship on open sand, then cutting it apart by hand with gas torches, a dangerous operation that results in injuries and fatalities, as well as exposure to toxic materials such as asbestos, lead, and various chemicals.

The practice of taking passengers aboard cargo ships, once almost universal, is very rare today and almost non-existent on bulk carriers.

[7] If a hold is full, a technique called tomming is used,[8] which involves digging out a 6 feet (2 m) hole below the hatch cover and filling it with bagged cargo or weights.

Larger bulk carriers, from Handymax up, usually have a single two-stroke low-speed crosshead diesel engine directly coupled to a fixed-pitch propeller.

On the smaller bulk carriers, one or two four-stroke diesels are used to turn either a fixed or controllable-pitch propeller via a reduction gearbox, which may also incorporate an output for an alternator.

This standard requires that the pressure due to sea water be calculated as a function of freeboard and speed, especially for hatch covers located on the forward portion of the ship.

Comparing a ship's carrying capacity in terms of deadweight tonnage to its weight when empty is one way to measure its efficiency.

[79] Since the adoption of double hull has been more of an economic than a purely architectural decision, some argue that double-sided ships receive fewer comprehensive surveys and suffer more from hidden corrosion.

[4] Places subject to the largest stresses are studied carefully, such as hold-bottoms, hatch-covers, bulkheads between holds, and the bottoms of ballast tanks.

[4] Great Lakes bulk carriers also must be designed to withstand springing, or developing resonance with the waves, which can cause fatigue fractures.

The rules apply to bulk carriers more than 90 meters in length and require that scantlings' calculations take into account items such as the effect of corrosion, the harsh conditions often found in the North Atlantic, and dynamic stresses during loading.

[12] Due partly to the sinking of MV Derbyshire, a series of international safety resolutions regarding bulk carriers were adopted during the 1990s.

[88] When very fine concretes and aggregates mix with water, the mud created at the bottom of the hold shifts easily and can produce a free surface effect.

[7] The 1997 additions also required bulk carriers with restrictions (for instance, forbidden from carrying certain types of cargoes) to mark their hulls with large, easy-to-see triangles.

[95] Since December 2004, Panamax and Capesize bulk carriers have been required to carry free-fall lifeboats located on the stern, behind the deckhouse.

[96] One argument against the use of free-fall lifeboats is that the evacuees require "some degree of physical mobility, even fitness" to enter and launch the boat.

[97] In December 2002, Chapter XII of the SOLAS convention was amended to require the installation of high-level water alarms and monitoring systems on all bulk carriers.

This safety measure quickly alerts watch standers on the bridge and in the engine room in case of flooding in the holds.