The National Transportation Safety Board (NTSB) has released a preliminary investigation report on the accident where the Francis Scott Key Bridge in Baltimore collapsed following a collision with the container ship MV Dali.
The Dali was propelled by a single, slow-speed, 55,626-hp (41,480-kW) diesel engine manufactured by Hyundai MAN B&W. The engine was directly connected to a single, right-turning propeller. To run the main engine, one of the vessel’s four diesel generators must be operating and supplying the vessel with electrical power. The emergency generator alone cannot be used to restart or run the main engine. The Dali’s main engine required compressed air directed into its cylinders to start and change direction. To change from ahead (moving forward) to astern (moving in reverse), the engine would need to be stopped and then restarted in the opposite direction.
The engine was also fitted with alarms and automatic shutdown features to prevent damage to the engine if supporting systems required for its operation, such as the lubricating oil pump (which controls lubricating-oil pressure) or cooling water pump (which supplies a flow of cooling water), were lost. If a loss of electrical power occurred to either of these pumps, the engine would be shut down automatically. As part of a multistep sequence to restart and operate the main engine after a shutdown, the lubricating oil and cooling water pumps would need to be restarted.
Dali’s Electrical Power Distribution System
The ship’s electrical power was supplied by four alternating current generators, which were each driven by a diesel engine. Generator nos. 1 and 4 were rated for 4,400 kW, and generator nos. 2 and 3 were rated for 4,000 kW. 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 (a propulsor on the ship’s bow that that assists with ship maneuverability), and reefer containers (refrigerated containers that cool temperature-sensitive cargo). The HV main electrical bus could be split with an installed main bus tie, which would isolate two generators on each side of the bus. The bus was designed to be normally operated in a closed-bus configuration (meaning the main bus tie, which connected the two sides of the bus, was closed); this was the case during the accident voyage.
Ongoing Activities
The NTSB will continue evaluating the design and operation of the Dali’s power distribution system (including its breakers). Examination of damage to the vessel will continue when the ship is clear of debris and moved to a shoreside facility. The NTSB is working with parties to immediately assess their bridges and determine whether pier protection needs to be improved. Specifically, the MDTA is studying short-term and long-term options for upgrades to the existing protection system for the eastbound and westbound spans on the Gov. William Preston Lane Jr. Memorial Bridge (commonly known as the Bay Bridge) near Annapolis. The NTSB is examining the pier protection improvements that have been made on the following bridge collapses resulting from marine vessel strikes that the NTSB has investigated: the Sunshine Skyway Bridge in Tampa Bay, Florida; Queen Elizabeth Causeway Bridge near South Padre Island, Texas; and the I-40 Bridge near Webbers Falls, Oklahoma.
Interviews, including with bridge experts, waterways management personnel, marine safety and highway regulators, and vessel operators, are planned. Detailed analysis of the VDR bridge audio and further validation of VDR parameters continues. Planned areas of investigation include oceangoing vessels’ propulsion and electrical systems; the frequency and causes of vessel contacts with bridges over navigable waters; and bridge-strike mitigation measures such as a combination of vessel-size restrictions, vessel-assist tugs, and bridge-pier protection. The NTSB investigation of all aspects of the accident is ongoing as they determine the probable cause.
Download the preliminary report: NTSB Investigation Contact of containership Dali with Francis Scott Key Bridge
