Baltimore Francis Scott Key Bridge collapse

[floobydust]

NTSB Marine Investigation Preliminary Report May 14, 2024 is out, with good info on what happened (but not the cause).
I thought it strange the LV transformer TR1 primary and secondary breakers tripped at the same time. Redundant system but was brought up a bit uh odd and too late.

[SiliconWizard]

Interesting read.

[tom66]

"The road maintenance inspector had been walking the length of the bridge
when the ship struck it. He ran north and made it to the nearest surviving span before
the rest of the bridge collapsed."

Hell of a story.  I'd buy a lottery ticket if I were him.

[NiHaoMike]

I find it hard to believe it would be designed such that a single transformer would be a single point of failure for all 3 steering pumps. Had one of the steering pumps been mechanically driven from the propeller shaft (including turning at a reduced rate from the momentum of the ship after the engine shut down), might it have side scraped the bridge or missed it altogether instead of a head on collision?

[SiliconWizard]

The trajectory was very unfortunate. They headed up straight to the pier and avoided (by not much) the dolphin that was supposed to be a first protection. (Not sure the dolphins for this bridge would have done much for a ship this size, but who knows, maybe that would have been enough to at least change its trajectory a bit.)

[coppercone2]

I find it hard to believe it would be designed such that a single transformer would be a single point of failure for all 3 steering pumps. Had one of the steering pumps been mechanically driven from the propeller shaft (including turning at a reduced rate from the momentum of the ship after the engine shut down), might it have side scraped the bridge or missed it altogether instead of a head on collision?

i swear try to get that installed at a engineering job, the only things thats gonna churn mechanically is your stomach.

you will get the randomly generated risk matrix with no defined units for the axis (I only figured out their actually related to cost and seniority level)

[Ice-Tea]

I find it hard to believe it would be designed such that a single transformer would be a single point of failure for all 3 steering pumps. Had one of the steering pumps been mechanically driven from the propeller shaft (including turning at a reduced rate from the momentum of the ship after the engine shut down), might it have side scraped the bridge or missed it altogether instead of a head on collision?

There is a second set of trafos and they actually managed to get those online. In addition, the EG powered up and remained active which seems to have allowed one of the steering gear pumps to remain active throughoput subsequent blackouts. Not mentioned in the report but it seems teh EG was a bit slow in coming online maybe.

Efficiency of a rudder at low speeds is poor, though, without a propeller to "force" things a bit.

[coppice]

I find it hard to believe it would be designed such that a single transformer would be a single point of failure for all 3 steering pumps. Had one of the steering pumps been mechanically driven from the propeller shaft (including turning at a reduced rate from the momentum of the ship after the engine shut down), might it have side scraped the bridge or missed it altogether instead of a head on collision?

People aren't very good at spot the SPOF at the best of times. When there is a cost saving they suddenly get much worse. I once worked with some FEMA (Failure mode and effect analysis) people who usually worked for the nuclear power industry, and was horrified how easily they glossed over potential problems in the systems they were looking at for us. Nobody was pressuring them to dumb down their analysis. Quite the opposite. They were tasked to be as thorough as possible. It was just their modus operandi.

[S. Petrukhin]

I would think not only about engineering problems, but also that there are people who blow up bridges and pipes in other countries... 

[Kleinstein]

Spotting tricky accident scenarios is tricky. It is quite common to have external effects (e.g. thunderstorm, extreme temperature, high wind) to stress the system an multiple points. Suddenly multiple failures at different point get more likely than normally though.

It is a bit odd design with the main motor shutting down even with a rather short interruption of the generators or just a breaker to trip, which likely can be for multiple reasons, not just overcurrent. They should have tested the effect of power interruption on stearing. It is not that there was something really unusual failing and the emergency generator was only a little late to start. To me this open the question why the design was accepted at all.

[dietert1]

There are many non-redundant parts like the main engine, the rudder, the HV power bus, the LV power bus. Also the rudder depends on the main engine and everything depends on the electrical power buses. Seems the HVR and LVR switches that pretend redundancy were useless.
The report explains that the bow thruster is connected to the HV bus, but don't mention it later. Did DGR3 and DGR4 trip when the thruster was turned on?

Regards, Dieter

[Kleinstein]

AFAIK the bow thrusters are only effective at very low speed, like when departing from the dock. At the relatively high speed the thrusters should not be really effective. So chances are the thrusters were never started in the accident.

At least the plan shows a way to split the HV and LV bus in a left and right part to use. So they should be able to use only half the buses, but than with a fixed combination of genrators and transformer.

For me the surprising point is that the loss of the main engine caused the vessel to turn so fast that they could not counteract with the rudder driven by the emergency generator. The electrical outage was the trigger, but it looks there was more wrong than just the electric.

[S. Petrukhin]

Such massive vessel could not independently change its trajectory. Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.
In order for the course to change, it is necessary to apply force. It's just ordinary physics.
The conclusion suggests itself: technical malfunctions do not matter, since there was an incorrect select for the trajectory of movement.
At least in the adjacent section of the fairway.

[Andy Chee]

Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.

Water currents are often NOT straight.

[JustMeHere]

Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.

Water currents are often NOT straight.

Yeah.  There are two rivers involved in this.

[S. Petrukhin]

Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.

Water currents are often NOT straight.

A significant remark... I thought there a bay and no tangible currents.

[dietert1]

AFAIK the bow thrusters are only effective at very low speed, like when departing from the dock. At the relatively high speed the thrusters should not be really effective. So chances are the thrusters were never started in the accident.
..

Yes exactly: They were in a harbour and slow. When space is limited, a tail rudder is of little use anyway. Before changing course by turning the ship around its vertical axis the rudder drags the ship exactly to the wrong side. I was wondering whether a 7 kW bow thruster running for some minutes could have avoided the collision or modified the impact enough to save the bridge.

Regards, Dieter

[Ice-Tea]

It is a bit odd design with the main motor shutting down even with a rather short interruption of the generators or just a breaker to trip, which likely can be for multiple reasons, not just overcurrent. They should have tested the effect of power interruption on stearing.

It's impossible to counter every eventuallity. If you have a blackout on a ship like this when manouvring its pretty much a given you're goig to have some egg on your face. Adding more layers of redunancy may even be counter-productive (more shit that can break). There's even an argument to be made that that already played a role here. Seems they switched to the other set of trafos the day before which then failed. If they had only had the single set of trafos they had been using before, this would not have happened.

AFAIK the bow thrusters are only effective at very low speed, like when departing from the dock. At the relatively high speed the thrusters should not be really effective. So chances are the thrusters were never started in the accident.

In addition, they run on electricity. Lots of it. Like, lots. Not something you're going to run in a blackout (obviously) or when just recovering from it.

Yes exactly: They were in a harbour and slow. When space is limited, a tail rudder is of little use anyway. Before changing course by turning the ship around its vertical axis the rudder drags the ship exactly to the wrong side. I was wondering whether a 7 kW bow thruster running for some minutes could have avoided the collision or modified the impact enough to save the bridge.

You're off by an order of magnitude. They had a 3MW bow truster.

[dietert1]

Even better. They could have tried, i mean they had nothing else. Probably at time they were half asleep and thought they can do nothing.

[Ice-Tea]

Not really. Again, the bow truster needs electricity. Which they had not.

[dietert1]

If you read the report, that's just not true. The diesels on the HV bus were running and the LV bus was operative, too, except a short period. At the time of the crash the ship had illumination.

[Kleinstein]

The balckout was from the brakers at the transformer tripping. From the reports the genrators were still running OK and thus the high voltage supply electricity from which the bow thruster would run still active. The problem with the bow thrusters is more that they are for really low speed, like  < 1 knot and they loose effect when going much faster. When they lost power the ship was running at some 8 knots and thus not that slow any-more.
Similar the tug boats would have to litte power to make a real difference at that speed. The habor tugs are made for low speed. So keeping the tugs would also require the ships to go slower.

Such massive vessel could not independently change its trajectory. Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.
In order for the course to change, it is necessary to apply force. It's just ordinary physics.

The propeller from the main propulsion not only provides the main propulsen, but as an unwanted side effect also a sideways force. When going straight under power the rudder (or a asymmetric hull shape ) has to compensate for this. When the motor (und thus the propeller) stopps, chances are that the propeller slows down the ship a little and produces an opposite side force too.
So the main engine stop not just slows down the ship, but also makes the ship turn. To keep the ship straight after the power loss they need a correction by the rudder.
My point is that this is not a surprising effect and the emergency generator should get steering back fast and powerfull enough to not get such a large excursion from the normal course.

In addition there was also some (though not very strong) wind pushing the vessel to the side it finally went. The the propulsion is lost the rudder gets less effective and thus additional correction needed.

Even in just a "bay" there can be quite some tidal currents. With the shipping channel and relatively shallow otherwise I would not expect the currents to be much sideway though. At least the pilots should have known (such local knowledge is the main reason for habor pilots) and we would have heard about this.

[soldar]

Even better. They could have tried, i mean they had nothing else. Probably at time they were half asleep and thought they can do nothing.

I take this as a throwaway comment without intention of substance but all indications are that the crew, including the pilot, acted very well, very professionally. Nobody was "half asleep". They acted fast and correctly.


https://www.washingtonpost.com/dc-md-va/2024/03/26/pilot-anchor-turn-baltimore-bridge-collapse/

Pilot on board the Dali tried to slow ship before it struck Key Bridge

The specially trained pilot ordered the rudder turned hard to the left and an anchor drop to steady the ship and slow it down, an industry official said

[Ice-Tea]

The balckout was from the brakers at the transformer tripping. From the reports the genrators were still running OK and thus the high voltage supply electricity from which the bow thruster would run still active.

Yes, but there was no means to activate the truster as the LV bus was down (and thus navigation). When the EG kicked in there was a small window where they could have used the bow truster but following a blackout of (at that time) unknow origin you don't exactly wan't to dump a 3MW load on the HV bus (aside from it being, as you mentioned, probably being of little use at higher speeds). At the very minimum the bridge would have had to contact the ER and those fellows were kinda busy. It would also have been a shortlived triumph as shortly after that a second blackout occured, this time tanking the DGs and thus the HV bus (which is kinda weird, there doesn't seem to be an actual reason for them to go down).

TBH, it looks like pretty much everyone did what they could do with the time and lack of hindsight offered to them.

[soldar]

Such massive vessel could not independently change its trajectory. Even if it is allowed to drift, it will continue to move on the same course. Keep moving in a straight line.
In order for the course to change, it is necessary to apply force. It's just ordinary physics.
The conclusion suggests itself: technical malfunctions do not matter, since there was an incorrect select for the trajectory of movement.
At least in the adjacent section of the fairway.

You have no idea about the complexity of this. In the Bay there are river and tidal currents. A vessel is subject to a multitude of forces. The rudder, the prop, the proximity to the bottom and the irregular shape of the bottom, the currents, the wind, etc. You have no idea how complex it is.