International Grain Code

The International Code for the Safe Carriage of Grain in Bulk (the Grain Code) was adopted in 1991 and is mandatory under SOLAS Chapter VI, Part C. It applies to all ships, regardless of size, that carry grain in bulk. “Grain” is defined broadly to include wheat, maize, oats, rye, barley, rice, pulses, seeds, and processed forms that behave similarly. The Code was developed in response to numerous casualties caused by grain shift — the sudden transverse movement of grain surface layers when a vessel rolls, producing a heeling moment that can overwhelm the vessel's righting capability.

The Grain Code differs from the IMSBC Code in that it is specifically stability-based: its primary concern is the shift of the grain surface and the resulting heeling moment, not liquefaction. Grain does not liquefy, but it can shift catastrophically under the right conditions of roll, vibration, and surface void.

Document of Authorization (DoA)

Before any grain cargo can be loaded, the ship must hold a Document of Authorization issued by the flag state Administration or by a Recognised Organisation (RO) acting on its behalf. The Document of Authorization:

Confirms that the ship can carry grain in bulk and specifies any conditions or limitations (e.g., maximum grain loading in specific holds, mandatory compartment securing measures).
Is issued on the basis of a Grain Loading Booklet (or its equivalent) that has been approved as meeting the stability requirements of the Code. The Booklet contains pre-calculated heeling moment and void volume tables for each hold at various filling levels.
Must be available on board and produced on request to port state control. Vessels arriving to load grain without a valid Document of Authorization must not be permitted to load by the port authority.
Is not required if the Master demonstrates, using the general approval method of the Code, that the stability requirements are met for the specific voyage — but this requires a full calculation submitted to the Administration, which is impractical in most commercial situations.

Stability requirements

Angle of heel (θ) after grain shift≤ 12°
After the transverse shift of grain assumed under the Code, the resultant angle of static heel must not exceed 12°. This is the primary limiting criterion for grain loading.
Residual dynamic stability (area under GZ curve)≥ 0.075 m·rad between heel angle and 40° (or angle of flooding if less)
The area between the righting lever (GZ) curve and the heeling moment curve, measured from the angle of static equilibrium to 40° or the downflooding angle, must not be less than 0.075 m·rad. This ensures the vessel has sufficient energy reserve to resist capsizing after grain shift.
Initial metacentric height (GM₀) — corrected for free surface≥ 0.30 m
The initial GM corrected for the free-surface effect of all liquid tanks must not be less than 0.30 m at the departure condition. This is a baseline requirement; greater GM is often needed to meet the heel and dynamic stability criteria.

Compartment types and trimming requirements

Filled compartment (trimmed)
A hold that is filled to the maximum extent possible and trimmed to minimise the void space and level the surface.
Trimming must be carried out to fill all spaces under the deck and hatch covers as far as practicable. The residual void volume after trimming is used in the heeling moment calculation. No additional feeder provisions are required if the calculated heeling moment satisfies the stability criteria after assuming a 15% volumetric shift of the surface layer.
Partly filled compartment
A hold that cannot be filled to the full depth due to the cargo plan — typically a topside hold or a hold partially used for stowage sequencing.
Must be secured by one of three methods: (1) bagged grain or other suitable cargo laid over the grain surface to a depth of at least 1.2 m; (2) a longitudinal division (strapping or shifting board) extending at least B/8 from the centreline; or (3) overstowing with a calculated volume of non-grain cargo. The simplest compliant solution is bagged cargo on top.
Untrimmed compartment
A hold loaded through a single hatch without trimming — producing a peaked pile of grain with maximum void space around the periphery.
Treated as a partly filled compartment for stability calculation purposes, using conservative assumption of maximum void volume. The assumed transverse shift of grain surface is applied over the full void area. Untrimmed holds may only be permitted if the Document of Authorization specifically allows it and stability requirements are met.

Calculation summary

A Grain Code stability calculation proceeds in the following steps:

1. Void volume — Determine the void volume remaining in each compartment after loading and trimming. This comes from the approved Grain Loading Booklet tables for each hold and filling depth.
2. Assumed volumetric grain shift — The Code assumes a transverse shift equal to 25° of the void volume in filled trimmed compartments (or as specified for untrimmed/partly filled holds). This shift is converted to a transverse shift of the centre of gravity of the grain surface layer.
3. Transverse heeling moment (Mh) — Calculated for each compartment and summed. Mh = (assumed shift volume) × (grain density) × (transverse shift lever). The total Mh divided by the displacement gives the heeling arm (λ).
4. Angle of heel — The static heeling angle θ is found where the heeling arm λ intersects the GZ (righting lever) curve. Must be ≤ 12°.
5. Residual dynamic stability — The area under the GZ curve between θ and 40° (or downflooding angle), minus the area under the heeling arm line, must be ≥ 0.075 m·rad.
6. Longitudinal heeling moment — If holds are only partly filled, a longitudinal shift must also be checked to ensure the vessel does not develop a dangerous trim due to the shift of the grain surface in partially filled end holds.

Common grain cargoes

Wheat720–850 kg/m³Angle of repose 15–25°
Hard wheat has lower moisture sensitivity; soft wheat may compact and densify during the voyage, increasing void spaces and heeling moment. Among the most commonly shipped grain cargoes worldwide.
Corn (maize)700–800 kg/m³Angle of repose 18–27°
Relatively low bulk density and high angle of repose make corn prone to surface voids developing after compaction. Heavy loading from South America (Argentina, Brazil) and the USA.
Soybeans690–780 kg/m³Angle of repose 22–30°
Round beans flow readily; they can behave almost like a liquid when disturbed. Partial filling of holds without feeder/bagged grain provisions is particularly hazardous. High oil content makes them susceptible to heating.
Rice (paddy and milled)545–700 kg/m³Angle of repose 20–30°
Paddy rice (unhusked) is particularly prone to shifting due to husk lubrication. Milled rice is denser. Both may require fumigation for insect control, adding chemical hazard considerations.
Barley600–700 kg/m³Angle of repose 17–25°
Lighter than wheat; relatively high void fraction. Major export from Australia, Canada, and the Black Sea region. Can be subject to fumigation with phosphine.
Sorghum670–800 kg/m³Angle of repose 16–22°
Dense, round grain; low angle of repose, free-flowing. Mainly loaded in the USA and Australia. Void correction in stability calculations is important.

Grain Code vs national codes

USDA (United States) — The US Department of Agriculture issues its own grain loading regulations for ships loading grain at US ports. Masters must obtain USDA Form 319 approval prior to loading. USDA requirements are broadly consistent with the IMO Grain Code but may include additional requirements for specific commodities or terminal conditions. A ship with an IMO Document of Authorization may still need USDA approval at US ports.
AMSA (Australia) — The Australian Maritime Safety Authority applies the IMO Grain Code as implemented under Australian law. AMSA inspectors routinely check grain loading stability calculations and Documents of Authorization at major export ports (Fremantle, Port Kembla, Newcastle, Geelong). Australia is a major wheat and barley exporter, making AMSA grain inspections common for bulk carriers on the Australia–Asia trade.