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Bulk carriers load and discharge very large tonnages, often at terminal rates far faster than the ship itself can safely absorb without careful sequencing. The cargo itself is regulated by the IMSBC Code (International Maritime Solid Bulk Cargoes Code), mandatory under SOLAS Chapter VI, while the loading and unloading interface between ship and terminal is covered by SOLAS Chapter VI and Chapter XII (additional safety measures for bulk carriers) together with the BLU Code (Code of Practice for the Safe Loading and Unloading of Bulk Carriers, adopted by the IMO as Assembly resolution A.862(20)).
| Group | Hazard | Examples |
|---|---|---|
| Group A | May liquefy if moisture content exceeds the Transportable Moisture Limit (TML) | Iron ore fines, nickel ore, bauxite fines, mineral concentrates — see IMSBC Group A |
| Group B | Possess a chemical hazard (flammability, self-heating, toxicity, corrosivity) that could give rise to a dangerous situation | Coal, sulphur, certain fertilisers |
| Group C | Neither liquefy nor possess a chemical hazard, but not without their own stowage and loading-plan considerations | Lump iron ore, grain (also separately governed by the Grain Code), most agricultural bulk cargoes |
A cargo can be scheduled under more than one group (Group A and B together, for example) if it carries both hazards. The IMSBC Code schedule for the named cargo sets out the required certificates, stowage and segregation requirements, and — for Group A cargoes — the moisture-content declaration and testing regime.
A dense cargo loaded unevenly can overstress the hull long before the ship reaches its deadweight limit. The loading sequence is planned, and typically executed with a loading computer, to keep shear force and bending moment within the class-approved limits at every stage of loading — not only at the finished condition.
Modern bulk terminals can load cargo far faster than a ship’s own stress limits or ballasting capacity can safely absorb, so the loading rate and sequence are agreed with the terminal before cargo starts, and the ship can require the terminal to pause or slow loading into a given hold. Trimming — spreading the cargo evenly across the hold rather than leaving it in a cone under the loading spout — is required both for structural reasons (avoiding a concentrated local load) and, for Group A cargoes, to reduce the risk of a liquefied surface flowing toward one end of the hold. The BLU Code sets out the information exchange (cargo plan, rates, contingency arrangements) that should be agreed between ship and terminal before loading begins.
Between voyages, holds must be prepared to a cleanliness standard suited to the next cargo — ranging from a simple cargo-clean sweep to a full grain-clean wash, rinse and dry cycle inspected by an independent surveyor before the Notice of Readiness can be tendered. See bulk hold preparation for the grades, procedure and the laytime consequences of a failed inspection.
Group A cargoes shipped above their Transportable Moisture Limit can liquefy under the vibration of the voyage, producing a free-surface effect that has caused vessels to capsize. TML is set at a fixed margin below the Flow Moisture Point (FMP) established by laboratory testing, and cargo above TML must not be loaded. See IMSBC Group A for the physics, the testing methods and the cargoes most frequently implicated.
SOLAS Chapter XII requires bulk carriers to carry a loading instrument capable of calculating shear force and bending moment for the loading and unloading condition, approved by the flag administration or a recognised organisation. The loading computer is used to plan the sequence before cargo operations begin and to verify each intermediate step as loading or discharge proceeds, and its output is checked against the ship’s trim and draft as read from a draft survey.
Some bulk carriers are fitted with self-unloading gear — typically a system of hold conveyors feeding a boom conveyor that can discharge cargo directly to a shore stockpile or receiving hopper without shore cranes or grabs. Self-unloaders are common in trades (aggregates, coal, some grain) calling at terminals without heavy discharge equipment, and the unloading rate and sequence are managed from the ship rather than by the terminal, though the same hull-stress limits apply in reverse during discharge.
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