Second Video Transcript.
A little over a month ago, I made a video analyzing the incident involving the container ship Dali, which led to the collapse of the Francis Scott Key Bridge. On May 14th, 2024, the National Transportation Safety Board released a preliminary report, which confirmed many of the probabilities that I discussed in my video. In this episode, we will go through the technical side of the report, and I will provide further explanations for some of the details, which hopefully will make things a bit more understandable.
First up, the Dali’s main propulsion system. In this part, they describe the basic layout and properties of the ship’s main engine and generators. As mentioned here, the main engine is a 41,480 KW, two-stroke, Hyundai-MAN B&W diesel engine, and as typical for cargo ships, the main engine is directly connected to a right-handed propeller. This means that in order to change the ship’s motion from ahead to astern, the engine needs to be stopped and then restarted in the opposite direction. Yes, the engine can run backwards, and this is done by reversing the cylinder firing order.
In order to run, the main engine needs functional support systems like the lubricating oil pump and cooling water pump. These pumps are driven by electrical power, so if a blackout occurs and these pumps shut down, it will also trigger the automatic shutdown of the main engine as this is a safety feature to prevent damage to the engine parts that could be caused by a loss of lubrication or cooling. In order to restart the main engine, these pumps need to be restarted first. We should note that the fuel pumps are also electrically driven. So in case of a blackout, the fuel pumps will also stop and eventually cause the engine to stop as well.
Next, the electrical power distribution system. The Dali has four big generators, each driven by diesel engines. Generators one and four are rated at 4400kW, and two and three are rated for 4000kW. They are all connected to a 6600 volt high voltage main electrical bus or main busbar. Just for clarity, in the maritime industry, voltages above 1000V AC are considered high voltage. Now, in the report, it might get confusing as they oversimplified the electrical diagram. So I made my own drawing to make the explanation easier. As you can see here, the high voltage main bus distributes electrical power to all systems on board a ship, including the reefer containers and the bow thruster, and the step-down 440 volt transformers. I colored the lines red to indicate the high voltage, or 6600 volt line, black for the 440 volt line, and blue for the 110 volt line.
This busbar can also be split using the bus tie breaker, which can be used to isolate two generators on each side, but under normal circumstances this bus tie is kept closed. As mentioned, there are two step-down 440 volt transformers which connect to the low voltage 440 volt switchboard. Breakers are located on either side of the transformers. They named it HR1 and HR2 on the high voltage side, and LR1 and LR2 on the low voltage side. Machinery in the engine room, like the steering gear and the lube oil and cooling water pumps we mentioned earlier typically use 440V, so they are all powered from here. Another set of step-down transformers, either 110 or 220V are also connected here for lighting and other smaller electric and electronic devices. The report didn’t specifically mention which voltage, but that’s not really relevant to the situation. This 440 volt busbar can also be split with the bus tie breaker, which is also in “closed” position under normal circumstances. With this configuration, it is possible to use just one transformer, either TR1 or TR2, with its associated breakers.
Then of course, there is the emergency switchboard, which is also connected to the 440 volt bus by a circuit breaker. This emergency switchboard supplies power to designated emergency machinery and emergency lighting. Once the system detects no voltage coming from this line, the emergency generator automatically starts, subsequently disconnecting the emergency bus from the 440 volt switchboard, and then takes electric power from the emergency generator by closing the circuit breaker.
Next we go to the events of March 26th. During departure maneuvering operations, generators three and four were in service and supplying electrical power to the entire ship. As I mentioned in my previous video, this is the normal procedure and two generators can provide more than enough power for this operation. Generators one and two were on standby and under normal circumstances would automatically start in case either of the running generators tripped. All three steering gear hydraulic pumps were also running, which is also the usual procedure during maneuvering in order for the rudder to turn faster. As I mentioned earlier, I’ll focus on the engineering side, so I’ll be skipping the other portions for now. At around 0125 hours, the Dali was 0.6 miles from the Key Bridge when the electrical breakers HR1 and LR1 tripped. This effectively caused the first blackout and shut down the 440 volt Busbar, which practically powered everything, including pumps, the steering gear, and lighting. Subsequently, since the oil pumps and other ancillary systems stopped, the main engine also automatically shutdown.
So at this point, the ship had no propulsion and no steering. Remember, in my previous video, I mentioned that the most probable cause would be either a fuel problem or a switchboard problem. Well, here it is. Switchboard problem. But I honestly think there’s more to this than just faulty components. Apparently, generators three and four continued running and were still supplying power to the high voltage bus. This is possible because without any electrical consumers, the generators didn’t need a lot of fuel pressure. So even without fuel booster pumps, it was mostly being fed by gravity since the gas oil tanks are usually located on the upper floors of the engine room. However, even if there’s power in the high voltage 6600 volt bus, the 440 volt is where everything critical is connected. And since there was no physical connection at that moment, there was no flow of electricity to almost all equipment. This included the ship’s bridge equipment, which caused the Voyage Data Recorder to lose vessel system data feeds, except for bridge audio. The VDR has its own backup battery, though, so recording wasn’t affected.
Now, according to the crew, the emergency generator automatically started and connected to the emergency bus shortly after the blackout. But as we have seen in the footage, the navigation lights remained off together with all the other lights for about 59 seconds. If the emergency generator did indeed run and connect shortly after the blackout, we would have seen only the nav lights turn on first, followed by everything else once power was restored. But more on this later. As I mentioned before, if the emergency generator did indeed run and connect, one of the steering gear pumps, in the Dali’s case, the designated emergency steering pump was the number three, would have been available for use. This means the ship can turn the rudder, although at a slower rate of movement. However, as I mentioned in my previous video and as mentioned in the report as well, without thrust provided by the propeller, the rudder would be less effective, especially for a ship of this size. In any case, power was restored after 59 seconds, and apparently it was being supplied by generators three and four, which never stopped running. This means the ship had access to all of its equipment and effectively had full electrical power. This means they had three steering gear pumps functioning, but even with all three and the rudder responding rapidly to the helm commands, there was hardly any effect since there was no propulsion. I’ve read some comments in the previous video saying I was wrong, saying that the ship can turn even without propulsion. Well, maybe for smaller ships. Yes, it’s possible, but we’re talking about a massive ship with comparatively a very small rudder here. So the report confirms that they weren’t able to turn the ship, even with a functioning rudder. Now, as it turns out, the crew manually closed the breakers HR1 and LR1, which reconnected generators three and four to the 440 volt transformer and Busbar, effectively restoring power to all systems. In the CCTV footage, black smoke started coming out of the stack around 13 seconds after power was restored. Now, even though we know that two generators were continuously running even during the first blackout, I still find it hard to believe that the black smoke was caused by the sudden influx of electrical load. These are big generators with 8400 kilowatt capacity between them. They are certainly more than enough to handle a few pumps in the engine room. Black smoke could be a possibility, but maybe only for a few seconds and not continuously, as we can see from the CCTV footage. This might have something to do with the second blackout. From here, the report mentions the pilot giving various orders and dropping anchor. So I’ll just skip that. At about 0.2 miles from the bridge. A second blackout occurred because the circuit breakers for generators three and four opened. This caused a total power loss for both the high voltage and low voltage systems. This time the trip occurred from the generator breakers and not the transformer breakers. This means there was something wrong with both of the engines as they happened at the same time. These breakers will usually trip in case of engine overspeed or slowdown. The report didn’t mention the cause, but I’m leaning towards slow down due to fuel issues. Whatever it is, it’s something common to the two running generator engines and fuel is the most likely suspect. Now, remember what I said about the emergency generator and the navigation lights earlier? Well, as you can see, the emergency generator was already running and connected at this time since the navigation lights remained on during the second blackout. In my previous video, I said I found this strange, but now it all makes sense. They just kept the emergency generator running even when the power was restored the first time. At this point, the ship still had functional steering because of the emergency generator. But even though the pilot ordered the rudder hard to port, it wasn’t having any effect. Now, since the running generators actually tripped this time, this activated the auto start for generator number two, which was on standby mode. Its circuit breaker DGR2 closed and restored power to the high voltage bus. The report mentioned that the crew still had to manually close the breakers HR2 and LR2 for the 440 volt transformer TR2. In any case, the crew was able to restore power to the 440V bus around 31 seconds after the second blackout. However, they were still unable to regain propulsion. Then, shortly after, the Dali hit the bridge. It was also reported that around ten hours before the incident happened, the ship experienced a blackout while in port. Apparently, the crew was doing maintenance on the exhaust gas scrubber for the running generator at the time, and as per the report, a crew member mistakenly closed an inline engine exhaust damper. Of course, this is going to trip the engine as the exhaust gas won’t have anywhere to go. It’s like having your car’s exhaust pipe plugged. Now why would they do maintenance on a running system? I find it difficult to believe that they would do this. Also, mistakenly closing a damper. There are plenty of fail-safes in place against this, but okay, mistakes can happen. In the report, it says that generator number three automatically started and connected to the high voltage bus. Then vessel power was restored when crew members manually closed HR2 and LR2 breakers for the 440 volt transformer and the 440 volt Busbar. Again, I find this strange. Normally, the auto start sequence of the standby generators should not require human intervention to restore power to the 440 volt bus. So in all these generator trips, why did they have to manually reset the breakers for the Transformers too? Is it really designed to work like that? Because in the ships that I’ve worked on, the transformer breakers never trip unless there’s a problem with the transformer itself. Or in the rare case of differential protection. Another strange thing. Generator three continued running for a short period, but insufficient fuel pressure caused the speed to decrease, which then caused the generator’s breaker to trip. This actually sounds very similar to the second blackout just before hitting the bridge. As I mentioned in my previous video, generators share a common fuel line. Insufficient fuel pressure will only happen if the fuel tank was empty or the fuel booster pumps were not running. So did they forget to switch the fuel pumps on? If I’m not mistaken, the fuel pumps are included in the automatic sequential start. So they should have turned on almost immediately after power was restored. But even if it did not. This is basic. It’s the first thing you switch on. As for clogged filters, they were using low sulfur gas oil at this time, which is a clean fuel. So we can rule that out. Anyway, the NTSB is looking into the breakers for transformer one, which is the HR1 and LR1 because these two were in service when the first blackout after departure occurred. It was reported that transformer number two and its breakers, HR2 and LR2, have been in continuous service for several months prior to the incident. Only during the blackouts in port did they switch to transformer one. So they’re may be thinking the root cause might be a faulty component in that area. Ships have an alarm monitoring system in the engine control console. The alarm history can be found there, and it is an invaluable tool that can help the investigators figure out the sequence of events that led to the breakers tripping. They just need to sort through all of the alarms recorded, and there will be so many alarms that will have the same timestamp in the event of a blackout since all of the systems will have failed at the same time. In any case, as I said in my previous video, the two probable causes of these blackouts are either fuel related or switchboard related. From what we can see now, we were right in that assessment. The cause is somewhere in the electrical switchboard. But as per the report, I’m getting the impression that there were fuel related and procedural causes as well. Although secondary. Only the specific details remain unknown at the moment. Maybe in the next few weeks new information might come out, but until then we can only guess. I saw a comment that said he has read the NTSB report, but didn’t understand what he was saying. So I hope this episode answered a few questions or at least gave more clarity to the report. Thank you for watching and