Case Study: Captain's Sleep Inertia Led To Tow Striking Lock Gate

A captain assuming a watch immediately after waking led to a tow striking a lock gate in the Gulf Intracoastal Waterway, the National Transportation Safety Board said in Marine Investigation Report 22/09 released Tuesday.

On March 22, 2021, the towing vessel Ava Claire was transiting westbound pushing two fully loaded tank barges in the Gulf Intracoastal Waterway near Intracoastal City, Louisiana. After entering the Leland Bowman Lock, the bow of the lead barge struck a closed lock gate, damaging and disabling the gate. No injuries or pollution were reported. The lock gate sustained $2.5 million in damage.

On the morning of March 22, 2021, the captain awoke after 4.5 hours of sleep to assume the watch early from the vessel’s pilot. The pilot offered to take the tow through the Leland Bowman Lock, but the captain declined and took the helm about five minutes before maneuvering the tow into the lock. According to a policy contained in the vessel’s operations manual, a change of watch was not to occur during “a critical move,” such as maneuvering into a lock.

Ava Claire under way before the casualty. | *Image Credits: General Marine Services*

The tow struck the lock gate less than 30 minutes after the captain woke up. At the time, the captain was likely experiencing the effects of sleep inertia—the temporary feeling of grogginess felt immediately upon waking up. According to the report, as the master of the Ava Claire, the captain should have been familiar with the vessel operating policies and procedures and should not have taken the watch. However, his decision to take the watch may have also been the result of impairment caused by sleep inertia.

Additional factors added to the captain’s challenges as he attempted to maneuver the Ava Claire tow, including a tidal current pushing the tow from astern; loss of the GPS feed to the vessel’s electronic chart system which denied the captain his primary source of speed indication; and problems with radio communications between the deckhand and the captain further impacting his ability to judge speed and distance.

intracoastal map — Image Credits: ntsb.gov

The NTSB determined the probable cause of the contact of the Ava Claire tow with the Leland Bowman Lock gate was the towing vessel captain’s decision to assume the helm watch and attempt a predawn transit into the lock immediately after awakening while he was likely impaired by sleep inertia.

“Studies have shown that the effects of sleep inertia include reduced alertness, slower reaction time, less accuracy, degraded memory, and impaired decision-making ability,” the report said. “Sleep inertia generally lasts for about 30 minutes after waking but may last longer if a person is sleep deprived. Mariners should allow time to fully recover from sleep inertia before taking a watch and performing critical duties.”

Marine Investigation Report 22/09 is available online.

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