Bulk Carriers
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A bulk carrier, bulk freighter, or bulker is a merchant ship used to transport unpackaged bulk cargo such as cereals, coal, ore, and cement.
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Description
The Safety of Life At Sea (SOLAS) Chapter XI-Reg.1 defines a bulk carrier as a ship which is constructed generally with single deck, topside tanks and hopper-side tanks in cargo spaces. A bulk carrier is intended primarily to carry dry cargoes in bulk, and includes such types as ore carriers and combination carriers.
In general, a bulk carrier is a ship meant for carrying dry bulk cargoes such as ore, coal, grain, and having top side and hopper-side tanks with corrugated transverse bulkheads.
This design of bulk carrier are for the single skin type. In recent times there have been many double skin bulk carrier that were constructed. Another development in the recent times is the increase in size of these vessels (refer bulk carrier sizes).
History
Bulk carriers were developed in the 1950s to carry large quantities of non-packed commodities such as grains, coal and iron ore. Some 5,000 bulk carriers trade around the world, providing a crucial service to world commodities' transportation. Before this 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 of Bulk carriers
Apart from the size (refer bulk carrier sizes), bulk carriers can be categorized depending on the industry sector it is serving. The categorization include Steel industry (Iron ore, coking coal, steel, scrap, pig iron), Agriculture (Wheat, coarse grain, soyabeans, meal fertilizers, phosphate rock), Energy industry (steam coal) and Other industries (Bauxite, alumina, timber, minerals).
Another way of categorizing the bulk carrier is based on the machinery installed. The categorization include:
- Open hatch bulk carriers
- Geared Bulk Carriers
- Self-unloaders, etc.
Design features
Some of the important factors that play when the design of bulk carrier is done are as follows:
- Stowage factor
It is defined as space occupied by cargo in cubic meters per ton (or cubic feets per ton). This is the inverse of the average density of the cargo (ton/cubic meter). The designer has to note that when the ship is designed to carry heavy cargoes (like iron ore), the cargo volume is not the primary design criteria and conversely when the ship is designed to carry light loads (like grain), the cargo volume is a primary design criteria.
Design
The typical cargo hold of the bulk carrier is given here. The example given here is a of a single skin bulk carriers with double bottom. The double bottom and deck are longitudinally framed whereas the side shell in cargo hold are transversely framed.
References
- Ship Design & Construction by Thomas Lamb. Publisher SNAME
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