Lessons Learnt: Shifting of deck cargo in heavy weather

Vessel Type: Cargo Ro-Ro

Incident description

The vessel loaded an assortment of cargo consisting mainly of trucks, wheeled and tracked excavators, containers and other general cargo. The securing of the cargo was carried out by the crew, principally using chain lashings attached to the fixed strong points on both the interior main deck cargo space and upper external weather deck. During the voyage, heavy weather of up to BF 9 was encountered, causing the vessel to roll and pitch heavily despite the master's efforts to alleviate the motion by altering course and speed. When experiencing a particularly heavy roll, a single two tier stack of 40' containers on the weather deck was observed to shift by the OOW, which then impacted adjacent cargo. This set in motion a "domino effect" whereby cargo units progressively broke free and shifted, resulting in extensive damage to ship structure and cargo, with a number of units being lost overboard.

Analysis

A cargo shifting incident of this nature has the potential to endanger both the crew and the seaworthiness on the vessel. Although there was some criticism of the stowage arrangement with respect to the absence of suitable dunnage between the heavy excavator tracks and the weather deck plating, a serious deficiency in the manner the two containers were stuffed was likely to have played a role in initiating the incident. Both containers were loaded with machinery parts, none of which were properly secured within. Critically, a very heavy cast steel ballast weight was placed within the upper container, the free movement of which caused the stack to become unstable and impart severe racking forces on the lower container, resulting in the failure of the corner castings, twist-locks and lashings.

Lessons Learnt

• The safe carriage of containers and other general cargo is very reliant upon the shippers accurate declaration of weight, contents and the proper stowage of materials within the cargo unit
• Very dense, heavy cargo items should  not be carried in standard containers unless stowed on cradles which allow the cargo to be properly secured and spread the load
• The stowage of heavy containers on top of lighter containers should be avoided
• Cargo stowage and securing should be performed with reference to the Cargo Securing Manual, having in mind sound principles of good seamanship and based on the most severe weather conditions expected for the intended voyage