The National Transportation Safety Board found that improper stacking by Young Brothers caused 21 shipping containers aboard a barge to topple overboard June 22 near Hilo Bay.

The NTSB released a 12-page report on the barge incident, which caused a loss of $1.6 million in cargo and damage and container replacement.

The NTSB determined that the probable cause of the collapse of the container stacks on board the Hoomaka Hou was the company not providing a barge team with an initial load plan.

It also found that there were inadequate procedures for monitoring the stack weights. That led to the undetected “reverse stratification of container stacks,” and made the stacks more susceptible to the forces while in transit at sea.

The containers should have been stacked with the heaviest on the bottom and the lightest on top. Instead the reverse was the case.

Of the 21 shipping containers that went overboard, only eight were recovered. A total of 50 containers were loaded on the barge in Honolulu before heading for Hilo Bay.

Cargo loss was estimated at $1.5 million. Damage to the barge and containers was estimated at $131,000.

The incident occurred at 2:30 a.m. near Pepeekeo Point, 6.9 miles north-northeast of Hilo, at a depth of 750 feet.