Circuit breakers in the power management system of the boxship Dali (IMO 9697428) repeatedly tripped, leading to blackouts across the ship and a loss of propulsion and steering prior to the ship striking and destroying the Francis Scott Key Bridge over the Patapsco River, Baltimore, in the United States of America, on 26 March, the U.S. National Transport Safety Board has reported in a preliminary report. Further investigations are ongoing to determine the probable course.
A “circuit breaker” is a switch designed to protect an electrical circuit from damage caused by an over-current / an over-load or a short circuit and its function is to interrupt the flow of current, according to power management company Eaton. A breaker will “trip” or “open” when there is too much electricity flowing through it or when it cannot handle the electrical load any more, according to power management company Coastal Power systems.
The following information is taken from the NTSB Marine Investigation Preliminary Report of 14 May 2024: “Contact of Containership Dali with the Francis Scott Key Bridge and Subsequent Bridge Collapse” unless otherwise specified.
Dali’s propulsion and electrical systems
The Dali’s power was supplied by a single, slow-speed, 41,480kW diesel engine manufactured by Hyundai MAN B&W. The engine was connected to a single, right-turning propeller. To run the engine, one of the vessel’s four diesel generators (1-4) were needed to operate to supply the vessel with electrical power. The emergency generator alone cannot be used to restart or run the main engine.
The generators were rated between 4,000 kW and 4,400 kW and were connected to a 6,600 volt high-voltage main electrical bus by the vessel’s power management system, which controlled a range of shipboard equipment.
A 440-volt low-voltage electrical bus was connected to the high-voltage electrical bus via step-down transformers. The low-voltage bus powered vessel lighting and other equipment including steering gear pumps and the main engine cooling water pumps. Breakers were located on the high-voltage bus and the low voltage bus.
Loss of electrical power on the day before the collision
On 25 March 2024, about ten hours before leaving Baltimore, the Dali had a blackout with the loss of power to the high voltage and low voltage buses during in-port maintenance. Two in-port blackouts occurred. The first was caused by a crewmember mistakenly blocking the online generator’s exhaust gas stack. The second was related to insufficient fuel pressure for the online generator. The NTSB reports that it is still investigating the first in-port blackout and the potential impacts of the events of the subsequent voyage.
The “accident voyage”; breakers tripped; ship lost power
Generators 3 and 4 were supplying power. At about 01:25 am, when the Dali was about three ship lengths away from the Bridge, electrical breakers HR1 and LR1, which fed most of the vessel’s equipment and lighting, unexpectedly opened, cutting power to all shipboard lighting and equipment including the main engine cooling water pumps (which controlled engine cooling water pressure) and steering gear pumps. This was the first blackout.
The loss of electrical power to the pumps caused the main engine to automatically shut down and the vessel’s propeller stopped. The ship had now lost propulsion. The loss of power also meant that the rudder could not be moved; it was in an amidships (0 degree) position.
The report states that, according to the crew, the emergency generator started and connected to the emergency bus. The NTSB is investigating the exact timings of the emergency generator and and connection to the emergency bus. When the emergency bus was powered, emergency lighting, navigation and radio equipment, alarms and other emergency equipment would have been available and the emergency steering pump would have been available to turn the rudder at its low-speed setting. However, without the propeller turning, the rudder would have been less effective.
The crew manually closed the HR1 and LR1 breakers, which reconnected the generators and a low-voltage electrical bus and this restored power to the whole vessel.
When the ship was 0.2 miles from the bridge, a second blackout occurred because breakers DGR3 and DGR4, which connected the generators to the high voltage bus, opened. This opening caused a total loss of electrical power throughout the vessel. However the emergency generator was connected to the emergency bus and provided electrical power to the emergency equipment continuously through the second blackout. Generator 2, which had started automatically because it was in standby mode, connected and restored power to the high voltage bus.
About 32 seconds after the second blackout, the crew manually closed breakers HR2 and LR2, which restored power to the low voltage bus. The low voltage bus was being powered by generator 2. The crew restored electrical power before the vessel struck the pier but was unable to regain propulsion.
The ship then struck one of the piers of the Francis Scott Key Bridge causing six spans of the bridge to collapse.
Tugs
At 00:36, the two tugboats – the Bridget McAllister (65-ton bollard pull) and the Eric McAllister (66-ton bollard pull) pulled the Dali away from the dock. About 01:07, the vessel entered the Fort McHenry Channel and the pilot ordered for tugboats to be let go, which was normal practice. At 01:26:39 the pilots called for tug assist. The Eric McAllister was 3 miles away and answered, but did not reach the Dali in time.
Drugs & alcohol
No-one tested positive for alcohol when the Dali’s Master and the Dali’s Chief Engineer tested the whole crew at 02:32 on March 26 (i.e. approximately one hour after the collision), as per Coast Guard regulations. The two pilots were tested for alcohol and drugs at 05:30 and the result was negative. A third-party testing provider went aboard and tested the whole crew between 16:17 and 18:04 for alcohol and drugs and the crew and all results were negative, the report states.
Some commentators have criticised the amount of time it took for a third-party provider to test the crew (over 14 hours later); however, multiple medical and drug rehabilitation sources state that different types of tests can detect drugs and alcohol for many hours – even days – after consumption. Urine tests, it is reported, can detect alcohol for more than 24 hours (over 72 hours in the case of heavy consumption).
Fuel tests
After the collision, there was much speculation that there could have been issues related to contamination of fuel. The Dali used three main grades of fuel: low sulphur marine gas oil, low sulphur heavy fuel oil, and heavy fuel oil. There was about 1.8 million gallons of fuel in the tanks and none of the fuel tanks were damaged. The Dali had been running on low sulphur marine gas oil as per regulations. Testing of the low sulphur marine gas oil at an independent laboratory did not identify any concerns. Additional tests on samples taken from all fuel tanks and various manifolds did not identify any concerns with the fuel quality.
Pier protection
When the bridge was built, there were four large dolphins constructed to protect the bridge – two on the west side and two on the east side. The dolphins were built with a 25-foot-diameter sheet pile filled with tremie concrete and capped with reinforced concrete. There were 17-foot-long rubber fenders attached to the dolphins. The piers of the bridge were each surrounded by a 100-foot-by-84.5-foot crushable concrete box and timber fender system. The Dali did not contact the dolphin in front of pier 17 or its rubber fenders. The fendering systems were damaged during the collapse of the bridge.
Ongoing actions
The NTSB will continue to evaluate the design and operation of the Dali’s power distribution system. It will also assess bridges and options for upgrades to protect other bridges elsewhere. It is also examining protection improvements that have been made following bridge collapses resulting from marine vessel strikes that the NTSB has investigated on other occasions, namely, 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.
Further investigations are ongoing as the NTSB determines probable cause of the accident.
