Mechanical Problem Led to Towing Vessel Hitting Bridge
The National Transportation Safety Board has released a Marine Accident Brief about a February 11, 2019 accident involving the towing vessel Lindberg Crosby, which suffered a loss of engine control and struck the Interstate 10 bridge while attempting to dock an empty tank barge at the nearby Southwest Shipyard dock on the San Jacinto River in Channelview, Texas.
The NTSB determined that the probable cause of the incident was the undetected loss of starboard engine directional control due to a separation of the control system mechanical linkage to the pneumatic gear clutch, resulting in the engine not shifting in response to the operator’s commands.
As the vessel approached its intended berth just south of the Bridge, the captain attempted to slow the vessel by moving the throttles for both engines from ahead to astern. The port engine shifted astern, but unbeknownst to the captain, the starboard engine remained clutched in the ahead direction. The result was that the vessel began to veer to port. When the captain attempted to slow the vessel further by pushing the throttles further astern, the port engine responded with increased rpm astern as expected, but the starboard engine continued to push ahead which increased the rate of turn to port.
When the captain examined the starboard engine following the accident, he found that the threaded rod of the actuating piston had disconnected from the connector affixed to the shifting lever. This prevented any direction changes from being transmitted from the wheelhouse throttle levers to the shifting lever on the transmission. With twin propulsion engines and no positive feedback system to alert the operator that shift commands were not followed, the captain did not immediately discern the loss of starboard engine control and discovered it only after observing wheelwash coming from behind the starboard propeller.
Although it is unknown how long the pneumatic cylinder had been in operation or how many cycles it had actuated, the stamped numbers on the name plate indicate that the unit was built in 2006 and possibly overhauled in 2014. Following the accident, the company changed its policy from replacing units that had failed to replacing units at regular time intervals.
The NTSB wars operators of vessels using adjustable linkages that include jam nuts, locking nuts, or other devices that they should frequently examine the position of the nuts on shafts to verify their security and develop procedures to effectively ensure critical control system components are included in preventative maintenance programs.
The report is available here.