Reference
Bulk Carriers
Unpackaged dry cargo in volume. What it carries, how it is built and the limits that define the class.
- Cargo gear
- Geared on smaller sizes, gearless on the largest
- Capacity measured in
- Deadweight tonnes (DWT)
- Typical size
- From under 10,000 to about 400,000 DWT
- Cargo type
- Loose dry commodities
About bulk carriers
Single-deck ships built to carry unpackaged dry commodities poured straight into the hold — iron ore, coal, grain, bauxite, cement and fertiliser.
The hull is shaped by ballast tanks in the double bottom and in the topside and hopper wings, which give the hold its distinctive angled corners and help the cargo settle and self-trim as it is loaded.
Bulk carriers are described by size class rather than by design, and the classes are defined by what physically constrains the ship: a canal lock, a loading berth, or simply the depth of water. Those ten classes are listed below.
What it carries
How it is built
- A single-deck hull divided into large cargo holds, closed by weathertight steel hatch covers that roll or fold clear for grab and conveyor work.
- Ballast tanks in the double bottom and in the topside and hopper wings, which shape the hold and let the cargo self-trim as it settles.
- Corrugated transverse bulkheads between holds, stiff enough to take the pressure of a dense cargo without intermediate framing inside the space.
- Machinery and accommodation aft, leaving the full forward length of the ship for cargo.
- On geared ships, deck cranes or derricks between the hatches so the vessel can work in ports with no shore equipment.
Why it is used
- The cheapest way to move a tonne of dry commodity, because the cargo needs no packaging, unitisation or securing.
- Loading and discharge rates are very high where shore equipment is good — grabs, conveyors and shiploaders move thousands of tonnes an hour.
- Geared ships can trade almost anywhere, including ports with no cranes of their own.
- Hold arrangements are flexible enough to carry several parcels of different commodities on one voyage.
What to check before fixing
- Dense cargoes such as iron ore load the structure heavily and are subject to strict loading sequences to avoid overstressing the hull.
- Cargoes that can liquefy — some ore concentrates and fines — must be checked against their transportable moisture limit before loading.
- Draft and air draft govern which berths and waterways a ship can use, and both change with the season and the fresh-water allowance.
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