A bulk carrier is a ship type used to carry unpackaged cargoes. Bulk carriers are a form of merchant vessel, or cargo ship. The term bulk carrier can be considered as including liquids (LNG, oil, chemical tankers), however the preferred term for those vessels is liquid bulk carriers; hence, bulk carrier is generally synonymous with dry bulk carriers.
Bulk carriers tend to carry cargoes which, unlike tankers, are significantly denser than water. As such, the vessels are typically displacement limited.
Bulk carriers are amongst the simplest to build, typically exhibiting large sections of parallel midbody, full hull forms, and straight-forward divisions. They typically have a single deck and a double-hull, including hoppers and smooth-walled holds to minimize cargo which can't be unloaded. The wing tanks are typically ballast with fuel oil in the double bottom. Machinery is generally arranged aft with the superstructure (however ships which transit locks regularly will have the house forward, see great lakes frieghter).
Bulk carriers may be straight decked - loaded and unloaded from shore by buckets, or self unloaders, equipped with conveyors & derricks to unload themselves.
Bulk carriers tend to be large with high-density cargo loadings. It is important, when loading the vessel, that the holds be loaded in a manner which does not emplace undue stresses in the hull; either inherent stresses from uneven loading, or longitudinal stresses. Particularly when carrying heavier cargoes, the holds can look 'empty' when loaded to capacity, care must be taken so as not to overload the vessel.
There are many variants on the straight bulk carrier, not only in terms of capabilities, but also in terms of cargo. Combination carriers may use some of their holds for break-bulk or containerized cargo, or the wing tanks may be used to carry oil instead of ballast (see 'ore-bulk-oil' OBO carriers).