The NTSB issued an investigation report on the container damage and loss aboard barge Ho’omaka Hou, towed by Hoku Loa, while in the Pacific Ocean off Hilo, Hawaii, in June 2020. The investigation showed that an improperly loaded barge resulted in the loss of the 21 containers into the ocean.
The incident
On June 22, 2020, about 0230 local time, the deck cargo barge Ho’omaka Hou was under tow by the towing vessel Hoku Loa off the northeast coast of the big island of Hawaii en route to Hilo, when fifty 40-foot containers stacked on the after deck of the barge toppled, causing 21 to fall into the ocean.
There were no injuries or pollution reported. Eight containers were eventually recovered by salvors, and 13 remain missing. Cargo loss was estimated at $1.5 million, and damage to the barge and containers was estimated at $131,000.
Probable cause
The National Transportation Safety Board determines that the probable cause of the collapse of container stacks onboard the barge Ho’omaka Hou towed by the Hoku Loa was the company not providing the barge team with an initial barge load plan, as well as inadequate procedures for monitoring stack weights, which led to undetected reverse stratification of container stacks that subjected the stacks’ securing arrangements to increased forces while in transit at sea.
Main findings
The NTSB conducted a study to determine the locations of the centers of gravity for each stack in the collapsed row of containers on the Ho’omaka Hou based on the weights of each container as provided by the company.
The study showed that most were loaded in a manner that produced reverse stratification – meaning that heavier containers were loaded above lighter containers. Normal stratification is preferred because it creates a stack having the lowest possible center of gravity.
The containers were secured primarily with stacking cones, which provided little protection against the containers leaning or tipping.
It is 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 with the greatest reverse stratification, likely causing the containers to tip over, causing the row to collapse, the NTSB found.
An initial barge load plan showing stratified container weights would have been a useful tool to assist the barge team machine operators in stacking containers on the barge to reduce or eliminate reverse stratification, the report notes.
Even though machine operators stated they tried to stack containers with heavy containers on the bottom and light ones on top, neither the barge team member job descriptions or the company-provided Container Lashing Tips included instructions pertaining to the order in which to stack containers.
Instead, on the accident voyage, heavy containers in the collapsed row were consistently loaded over lighter containers, and stacks 1, 7, 8, and 10—which accounted for 20 of the 21 lost containers—were loaded almost exactly in reverse stratification.
In addition, the company did not provide the barge team procedures or calculations to determine if the lashing arrangements were sufficient for the reverse-stratified container stacks.
Lessons learned
-Sufficiency of Container-Securing Arrangements on Barges
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.
