Since non-cohesive bulk cargoes pose a risk of shifting, they can have a negative impact on vessel stability. To maximise safety, shippers should ensure that these cargoes are properly declared in accordance with the International Maritime Solid Bulk Cargoes (IMSBC) Code, says David Patterson, Loss Prevention Executive at North P&I Club.
In a recent case, a shipper incorrectly declared an angle of repose for a cargo of granulated pig iron, effectively declaring a cohesive cargo as non-cohesive. Because of the risk of shifting in transit, non-cohesive cargoes are subject to additional requirements under the IMSBC Code.
Cracking the Code
Firstly, it is important to understand the definitions provided in the IMSBC Code.
- Angle of repose means the maximum slope angle of non-cohesive (i.e. free-flowing) granular material. It is measured as the angle between a horizontal plane and the cone slope of such material.
- Cohesive material means materials other than non-cohesive materials.
- Non-cohesive material means dry materials that readily shift due to sliding during transport, as listed in Appendix 3 of the Code.
The cargo in question was declared by the shipper under the Bulk Cargo Shipping Name (BCSN) ‘IRON SMELTING BY-PRODUCTS’, the schedule of which states ‘not applicable’ for the angle of repose. However, the shipper contradicted this by including an angle of repose on the declaration, therefore declaring the cargo to be non-cohesive (free-flowing). Yet due to the highly irregular, non-rounded shape of the granules, the cargo was in fact cohesive and would not flow freely.
Identifying a non-cohesive cargo
Appendix 3 of the Code lists a number of cargoes that are non-cohesive when dry. Each individual schedule of the cargoes listed in this section states an angle of repose in the physical properties table and the trimming requirements in the loading section. Cargoes not listed in this section that exhibit properties of non-cohesive material are subject to the same trimming requirements as non-cohesive cargoes.
To allow their safe carriage at sea, non-cohesive cargoes are required to be suitably trimmed in accordance with section 5 of the Code. The level of trimming required is dictated by the cargo’s angle of repose. The lower the angle of repose, the more level the stow will need to be trimmed.
The unevenness of cargoes with an angle of repose greater than 35° is not to exceed 10% of the vessel’s beam with a maximum height of two metres. For cargoes with an angle of repose greater than 30° to 35°, this allowance is 10% of the vessel’s beam, but the maximum height is reduced to 1.5 metres. An alternative to these trimming requirements is to load the cargo using trimming equipment approved by the country’s competent authority.
Cargoes with an angle of repose less than or equal to 30° can free-flow like a grain cargo. For this reason, the Code requires these cargoes to be carried in accordance with the International Grain Code in addition to the requirements of the IMSBC Code.
Some examples of these cargoes are ammonium nitrate, grain screening pellets and urea. As well as complying with the grain regulations, the IMSBC Code requires the bulk density of the cargo to be considered when determining its securing arrangements and the influence of the free-surface effect on the vessel’s stability.
Checking the angle of repose
The angle of repose stated on the shipper’s declaration should be determined using a ‘tilting box test’. The details of this testing procedure can be found in Appendix 2 of the Code, which also provides an alternative testing method if a tilting box is not available. A check can also be performed by the Master, as the only equipment required is a horizontal table that is free from vibration, a sheet of rough-textured paper, a protractor, and a three-litre conical flask. This can prove an effective tool to ensure the cargo being loaded matches the angle of repose stated on the shipper’s declaration.
In summary, it is essential that cohesive and non-cohesive cargoes are correctly declared by the Shipper in accordance with the IMSBC Code. If a non-cohesive cargo is declared this will enable the Master to follow the requirements of the IMSBC code to ensure that these cargoes are loaded and carried safely.