An electrical generator set failure and subsequent loss of steering led to the grounding of a towing vessel near Greenville, Mississippi late last year, the National Transportation Safety Board (NTSB) said recently.
The towing vessel Marquette Warrior was pushing 35 loaded dry cargo barges down the Lower Mississippi River on November 21, 2021, when several barges grounded on the riverbank.
Four barges were damaged, including a hopper barge with bean cargo that partially sank. None of the nine people on board Marquette Warrior were injured.
The grounding resulted in US$1.24 million in damages to the vessel, barges and cargo.
As the vessel was transiting, the engineer saw flickering lights and a ground fault indication on the main switchboard.
The engineer then contacted the pilot in the wheelhouse to request the pilot stop the vessel so he could troubleshoot what he suspected was a problem with the electrical system. The pilot was not able to stop the vessel due to the size of the tow and its location.
The engineer identified an issue with the online port electrical genset. At the same time, the pilot noticed that he had lost steering control.
Hearing that the vessel had lost steering, the engineer decided to switch online gensets, which necessitated a temporary loss of the towboat's electrical power.
Although the engineer resolved the electrical issue by switching gensets and restored steering relatively quickly, the loss of steering in the swift current and limited manoeuvrability of the large tow prevented the pilot from avoiding grounding.
Electricians' analysis of the genset's alternator following the grounding indicated that the most likely cause of the failure was rubbing or chaffing of the sensing wiring harness, which led to arcing between terminal block posts, heat buildup, insulation failure, and eventual winding ring terminal connection failure.
NTSB investigators determined it is likely the chaffing of the wiring harness took place over the 72 hours the genset ran between a November 7 maintenance inspection and the grounding on November 21.
The NTSB determined the probable cause of the grounding was a loss of steering, likely due to a wiring harness within an electrical generator that was improperly positioned during a maintenance inspection. This resulted in the harness contacting the terminal posts, eventually causing the loss of three-phase electrical power to the steering pump motors.
"Proper operation and maintenance of electrical equipment is required to avoid damage to vessel critical systems and prevent potentially serious crew injuries, particularly for electrical systems with high and medium voltage and equipment with uninsulated and exposed components," the report said. "Electrical equipment should be installed, serviced, and maintained by qualified personnel familiar with the construction and operation of the equipment and the hazards involved."
