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The National Transportation Safety Board’s (NTSB) preliminary report on its investigations into the collision of the Dali containership with the Francis Scott Key Bridge in Baltimore on 26 March details a sequence of electrical power outages onboard the vessel prior to the event and also notes that tests of the ship’s bunker fuel did not flag up any concerns over quality.

The report notes the occurrence of two power outages onboard the vessel on 25 March, before leaving Baltimore.

About 10 hours before leaving port, the Dali experienced a power blackout during inboard maintenance. While working on the diesel engine exhaust scrubber system for the diesel engine driving the only online generator, a crewmember mistakenly closed an inline engine exhaust damper.

Closure of this damper effectively blocked the engine’s cylinder exhaust gases from traveling up its stack and out of the vessel, causing the engine to stall. When the system detected a loss of power, generator no. 3 automatically started and connected to the HV bus.

A second blackout in port was related to insufficient fuel pressure for the online generator. During both of these electrical power-loss events, the online generators’ breakers (DGR2 and DGR3) to the HV bus opened before the HR2 or LR2 breakers opened.

On 26 March, at about 0129 eastern daylight time, the 947-foot-long Singapore-flagged containership was transiting out of Baltimore Harbor in Baltimore, Maryland, when it experienced a loss of electrical power and propulsion and struck the southern pier supporting the central truss spans of the Francis Scott Key Bridge

The NTSB’s report notes that the ship’s electrical power was supplied by four alternating current generators, which were each driven by a diesel engine. The generators were connected to a 6,600-volt high-voltage (HV) main electrical bus by the vessel’s power management system (that powered various shipboard equipment, including the main engine lubricating oil pumps, the bow thruster and a reefer container.

About 0125, the Dali was 0.6 miles from the Key Bridge when electrical breakers (HR1 and LR1) that fed most of the vessel’s equipment and lighting unexpectedly tripped. This caused the first loss of electrical power) to all shipboard lighting and most equipment, including the main engine cooling water pumps (which controlled engine cooling water pressure) and steering gear pumps.

Generator nos. 3 and 4 continued to run and supply electrical power to the HV bus. Most bridge equipment also lost power, and the voyage data recorder (VDR) lost vessel system data feeds. However, bridge audio continued to be captured.

The main propulsion diesel engine was independent of the vessel’s four diesel driven electrical generators; however, the loss of electrical power to the pumps required for its operation resulted in the main engine being automatically shut down, and the vessel lost main propulsion.

The loss of electrical power stopped all three steering pumps, and, therefore, the rudder was unable to be moved.

The Dali’s crew was able to restore electrical power to the vessel, but, when the ship was 0.2 miles from the bridge, a second electrical blackout occurred because DGR3 and DGR4, the breakers that connected generator nos. 3 and 4 to the HV bus, opened, causing a total loss of vessel electrical power. At 0127:32, about 31 seconds after the second blackout, the crew manually closed breakers HR2 and LR2, restoring power to the LV bus, which was powered by generator no. 2.

The NTSB notes that the crew managed to regain electrical power before the vessel struck the pier but was unable to regain propulsion.

The report also details the subsequent testing of the bunker fuel onboard the Dali.The ship used three main grades of fuel for the main engine and electrical generators: low-sulphur marine gas oil (LSMGO), low-sulphur heavy fuel oil, and heavy fuel oil.

The Dali carried an estimated 1.8 million gallons of fuel in dedicated vessel fuel tanks and none of the vessel’s dedicated fuel tanks were damaged during the collision.

The last time the Dali crew switched fuel was on the evening of March 21, 5 days before the accident, when they switched to burning LSMGO in all engines upon entering US territorial waters.
The Dali subsequently bunkered various amounts of all three types of fuel in Newark, New Jersey, on 19 March after the month-long trip from Sri Lanka. Fuel-sample analysis results indicated that the LSMGO fuel bunkered in Newark complied with international standards and regulations. The test results did not identify any concerns related to the quality of the fuel.

On 28 March, samples were taken of the LSMGO that was being burned at the time of the accident. At the direction of the NTSB, the vessel owner transferred the samples to an independent laboratory. These test results did not identify any concerns related to the quality of the fuel.

Furthermore, on 11 April, additional fuel samples were taken from all fuel tanks and various fuel supply manifolds on board the vessel and these samples were tested by an independent lab.

Fuel-sample analysis results indicated that the LSMGO fuel being burned at the time of the accident complied with international standards and regulations. Once again, the test results did not identify any concerns related to the quality of the fuel.

While the cause of the catastrophic incident remains to be determined, the NTSB says that, as part of its ongoing investigations, it will continue to evaluate the design and operation of the Dali’s power distribution system (including its breakers).

Image: NTSB

AMERICAS: NTSB provides next update on Dali investigation

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