Bulk cargoes prone to liquefaction, like nickel ore, frequently cause problems. The biggest problem with these cargoes is caused by high moisture content. Although guidelines suggest that moisture levels be checked before loading, it is often difficult to be sure of these measurements and that they are indeed below the Transportaple Moisture Limit (TML).
Italian class society Rina has opted to promote a radical solution, which is for ships to be structurally modified or designed at the newbuilding phase to cope with cargoes that liquefy without dangling the vessel.
The International MAritime Solid Bulk Cargoes code rules say "cargoes having a moisture content in excess of TML should be carried in specially-constructed cargo ships or in specially-fitted cargoships".
Rina's new notation, IMSBC-A, is aimed at meeting these requirement, reflecting that a vessel's structure has been built or fitted to be safe to carry such ores and can withstand cargo liquefaction.
Specifically, the standard involves installing additional longitudinal bulkheads in some hold. The vessel retains capability to carry other dry bulk cargoes, with only a marginal impact on cargo-carrying capacity.
According to Dino Cervetto, head of technical services, for a typical supramax, two additional bulkheads are normally to be fitted in each hold where the carriage of nickel ore is foreseen.
"This means an extra weight ranging from 1,000 to 2,000 tones, depending on the number of holds involved. This does not affect in a significant way the ship's deadweight capacity, but reduces the cargo volume."
"Vessels would no longer have to rely on potentially unreliable moisture tests at the load port to determine if the cargo is safe to load or not," Mr Cervetto said.
Rina has produced a case study using a 55,000dwt supramax bulk carrier suitable for alternate loading. Structural changes involve installing two new longitudinal bulkheads in line with the hatch coaming in alternate holds to be used for cargoes prone to liquefaction.
Rina estimates the cost of conversion including an additional 1,800 tones-2,000 tones of steel, at about $3m, which it is said can be recouped quickly and generates a commercial benefit by giving greater flexibility in accepting cargoes as well as having crucial safety benefits.