Poor barge loading was the cause of the loss of 21 cargo containers into the ocean off the coast of Hawaii last year, the US National Transportation Safety Board (NTSB) has said in its report on the accident.
Barge Ho’omaka Hou, which was owned and operated by Young Brothers LLC, was being towed on June 22nd 2020 by the Hoku Loa and was about 6.9nm north-northwest of Hilo at the time the accident occurred.
The incident resulted in $1.6m in damage, but no injuries.
In Marine Accident Brief 21/09 the NTSB said that the probable cause of the collapse of container stacks onboard the barge was the company not providing the barge team with an initial barge load plan, as well as inadequate procedures for monitoring stack weights.
NTSB said that this “led to the undetected reverse stratification of container stacks that subjected the stacks’ securing arrangements to increased forces while in transit at sea”.
The NTSB conducted a study to determine the locations of the centres of gravity for each stack in the collapsed row of containers on the barge, based on the weights of each container as provided by the company.
The NTSB study showed that most were loaded in a manner that produced reverse stratification — meaning that heavier containers were loaded above lighter containers.
The containers were also primarily secured with stacking cones, which provided little protection against the containers leaning or tipping, the NTSB said. It was likely that, when the barge turned about 30 degrees to a new south-southeasterly course, the dynamic rolling from the seas on the vessel’s beam resulted in forces on the container stacks which had the greatest reverse stratification. This probably caused the containers to tip over, causing the row to collapse. “It is important for cargo planners to have tools, such as stow plans and calculations, to assist with determining proper stowage and the sufficiency of securing arrangements for containers stacked on barges. These tools should address the potential that container stacks may be stacked in a reverse stratified manner”, the NTSB report said