The origin of modern b.c. is not known explicitly. It is known that the first modern-type b.c. had topside and hopper tanks similar to modern dry bulk carriers. Before the introduction of the modern concept, double bottom structure was adopted for single deck ships in 1890. Triangular shaped topside tank structure was introduced for a cantilever-framed ship in 1905.

Types

Types of bulk carriers by size in deadweight are widely used in the industry. Four typical sizes are classified depending on the deadweight. That is, Capesize bulk carriers over 80.000 dwt, Panamax bulk carrier between 50.000 and 80.000 tons, Handymax bulk carriers between 35.000 and 50.000 tons, and Handysize bulk carriers between 10.000 and 35.000 tons. Handymax and Handysize bulk carriers are often referred to as Handysize bulk carriers.

Bulk cargoes are categorized depending on consumption sectors. Steel-related, agriculture-related, energy-related, and other sectors. Iron ore, coking coal, steel, scrap and pig iron cargoes are included in the steel related sector. Wheat, coarse grains, soyabeans, meal fertilizers, and minor cargoes are categorized as agricultural-related cargoes. Steam coal is used for energy-related sector, while bauxite, alumina, timber, minerals are used for particular purposes. There are five major dry bulks among them, which are iron ore, coal, grain, bauxite and alumina, and phosphate rock. Iron ore and coal are the raw materials for making steel. Grain is required for making many food products and the raw material for farming of cattle. Bauxite and alumina are the raw materials for aluminum making. Phosphate rock is the bulk fertilizer for crop production. Shipping of the major cargoes has significantly influenced the types of bulk carriers in the market.

Bulk carriers of 70.000 dwt and above carry most of the bulk cargoes increasingly in recent years, whil handysize bulk carriers show continuous reduction since 1975. This single commodity of bulk cargoes are carried under long-term contracts.

Handysize bulk carriers carry more other categories than iron ore, coal, and grain while panamax and capesize bulk carriers mostly transport coal and iron ore.

There are some variants of bulk carriers, such as open hatch bulk carriers, geared bulk carriers having cranes on deck, self-unloaders, etc. Open hatch bulk carriers, having box-shaped midship sections similar to conventional containerships, have been developed for carrying forest products. Onboard gantry cranes are equipped for efficient cargo handling. Since open hatch bulk carriers transport damage-prone cargoes such as paper roll, it is very important to have smooth surfaces of cargo holds.

A geared bulk carrier has deck machinery in order to discharge cargoes. If cargoes are unloaded without shore equipment, a geared bulk carrier may efficiently be used for multi-purpose operation by using grab and crane combinations. For loading and unloading operations at smaller harbors, handysize bulk carriers up to 50.000 dwt are widely employed.

Self-unloading bulk carriers were invented for efficient unloading of cargoes over grab methods in case of short voyage to specific ports. The vessels have a gravity-fed belt conveyor. The bottom of a hold has hopper tanks and is fitted with hydraulically operated gates. Large size self-unloaders can be used at shallow draft in order to transport cargoes to most ports in the world. The vessel operation is less affected by congested port facilities and unloading rates are very high.

Hull Form, Propulsion, and Performance

Hull forms of b.c. have the characteristics of comparatively slow, large block coefficient, long parallel middle body, and rectangular shape of the midship section. Simple hull forms with long parallel middle body contribute to easy manufacturing because of flat and single curvature lines.

The installation space for propulsive machinery is usually secured in aft engine room area. Fuel oil tanks are usually arranged in the engine room area so as to avoid installation of additional piping lines to double bottom tanks in the cargo hold region. Most modern bulk carriers have bulbous bows for the reduction of wave resistance.