Baltimore Francis Scott Key Bridge collapse

[soldar]

The San Francisco Bay Bridge was hit by a ship similar in size to the ship that hit the Key Bridge and the damage to the bridge was minimal. This was an ecological disaster due to the collision spilling 50,000 gallons of bunker oil into the bay, but no injuries on the bridge or on the ship.

Well, yes, but... In this case they built the bridge the way they did and I assume they had their reasons. Probably cost was a major consideration. Probably today it might be done quite differently. To make a large enough island to protect the supports you might have had to widen the span of the bridge more than was considered economical or practical at the time of it's design.

I mean, I tend to trust the people who designed it because they had the knowledge and information. I try not to second guess unless the flaws or faults are blatantly clear and obvious.

At the time the engineers thought it was a reasonable compromise and the fact that it has gone for so many decades without this accident kind of supports their choice. It is a one in a million chance and if it did not happen this time the bridge would most likely have served its life without a similar thing happening.

Engineers have to make choices with how to best use the budget they are given and after any accident there will be those who will say it could have been prevented if only they had spent more on this or that. It is just not economical to try to prevent everything that could possibly happen. Note also that the ship was already outside of the dredged channel and running aground (and slowing down).

[NiHaoMike]

Any info on how the steering system of the ship works? I'm surprised it doesn't have enough redundancy to prevent this, in particular a backup turbine (analogous to the RAT on an aircraft) powered by the momentum of the ship itself.

[SiliconWizard]

Any info on how the steering system of the ship works? I'm surprised it doesn't have enough redundancy to prevent this, in particular a backup turbine (analogous to the RAT on an aircraft) powered by the momentum of the ship itself.

So am I.

[soldar]

Any info on how the steering system of the ship works? I'm surprised it doesn't have enough redundancy to prevent this, in particular a backup turbine (analogous to the RAT on an aircraft) powered by the momentum of the ship itself.

I guess it is most probably hydraulic and I think an emergency engine and pump would make more sense. I live next to a hospital and as soon as the electric power fails an emergency generator starts automatically. On a ship that size I would expect a standby system that guarantees the proper working of all essential functions. It may be that the ship did have them but they were not adequately maintained.

I am always surprised by how emergency systems are not functional when needed. Like when there is a fire in a crowded place and the emergency exits are locked and people die.

[cosmicray]

The Skyway collapse changed bridge design.

The Sunshine Skyway Bridge (entrance to Tampa Bay) came down in 1980. The FSK Bridge (that collapsed today) was built during the 1970s, so before the Skyway lessons were learned. The Sunshine Skyway Bridge (the current one) has dolphins surrounding the support columns. We live and we learn. The original Skyway Bridge lasted about ~25 years (originally there was a single span, then a second was added). The FSK Bridge survived for ~50 years. Properly taken care of, it might be still standing, other than for the vessel collision.

I grew up around Tampa Bay. The original SSB scared me. The new one is much better, but it's still a long way down to the water.

[cosmicray]

In my estimation removing the wreck of the bridge is the most urgent task so that maritime traffic can be restored. We shall see how long that takes but I am generally quite impressed by how quick the feds deal with this kind of thing.

Vehicular traffic still has a tunnel under the Bay a bit farther north and another bridge a bit to the south so, while inconvenient, it is not terribly bad.

US Army Corp of Engineers has been tasked with restoring the shipping channel, which includes the removal of the wreckage. I'm assuming they will be working with the owner of the ship and the port of Baltimore, to have the ship carefully withdrawn from the accident location.

Somewhere today it was mentioned that hazardous cargo that could cross the bridge, may not be allowable in the tunnel. So that is a complication that needs to be sorted out.

[soldar]

US Army Corp of Engineers has been tasked with restoring the shipping channel, which includes the removal of the wreckage. I'm assuming they will be working with the owner of the ship and the port of Baltimore, to have the ship carefully withdrawn from the accident location.

Somewhere today it was mentioned that hazardous cargo that could cross the bridge, may not be allowable in the tunnel. So that is a complication that needs to be sorted out.

I had not thought of hazmat but in the big scheme of things those vehicles can go around. Still, it the Key bridge being out of service will mean additional traffic on the other bridge and the tunnel and may lead to traffic jams, etc.

I would think getting the ship out of the way is the easier part and removing the wreckage of the bridge is more complicated. Or maybe not. I suppose the first thing is to get everything out of the channel and not necessarily out of the water.

I wonder how hard aground the ship is. I am reminded of the Evergrande ship that went aground in the Suez canal and they had quite a hard time getting it afloat again.

As for the wreckage of the bridge, I suppose it can be cut up so it  is easier to move. Still, quite a task.

But clearing the channel and making it navigable again is, in my view, the most urgent task with great difference. Lots of ships are waiting to get out and to get in and waiting idle costs money.

[EEVblog]

Well, yes, but... In this case they built the bridge the way they did and I assume they had their reasons. Probably cost was a major consideration. Probably today it might be done quite differently. To make a large enough island to protect the supports you might have had to widen the span of the bridge more than was considered economical or practical at the time of it's design.
I mean, I tend to trust the people who designed it because they had the knowledge and information. I try not to second guess unless the flaws or faults are blatantly clear and obvious.
At the time the engineers thought it was a reasonable compromise and the fact that it has gone for so many decades without this accident kind of supports their choice. It is a one in a million chance and if it did not happen this time the bridge would most likely have served its life without a similar thing happening.

That would be my guess as well.
Engineering is the art of practical compromise.

[soldar]

That would be my guess as well.
Engineering the art of compromise.

Also, safety is a relative and changing concept. In the late 19th century, in the age of sail, it was considered quite normal to lose a sailor or two on a long voyage. they climbed the rigging and accidents were common. If a sailor fell on deck he was probably dead or maimed for life. If he fell in the water the chances of recovering him were slim... even if they tried and many times they didn't because it might be considered too risky with little chance of recovering him.

Up into the 1930s building bridges and other structures the risk of death was just considered part of the job. No safety equipment and no real accident prevention. It was a very different mentality.

Today we build a tunnel and it is two tunnels plus one or two service tunnels, etc. And build with much greater safety in mind. The culture has changed. Electrical appliances and installations from 60, 80, 100 years ago were extremely dangerous by the standards of today.

It is easy to see how the mentality of safety in general has changed in developed nations. Just go to some third world countries and you still see a mentality that any money or effort expended in safety and prevention is money and effort wasted.

Safety costs money and it is good if you can pay for it. The richer we become the more safety we can afford. Which is good.

[soldar]

I notice an electric line running parallel to the bridge and the pylons are well protected by caissons. Still, they are in shallower water, farther away from the dredged channel. If they were hit by a ship that size I doubt they would survive.

[BrianHG]

Closeup view of crash.  The ship appears to have it's power go off and on 3 times up to the crash...


Areal reconnaissance the next day.

[EEVblog]

Safety costs money and it is good if you can pay for it. The richer we become the more safety we can afford. Which is good.

But there is still going to be practical compromise at some point, that six sigma does only get you so far.

[fourfathom]

The San Francisco Bay Bridge was hit by a ship similar in size to the ship that hit the Key Bridge and the damage to the bridge was minimal. This was an ecological disaster due to the collision spilling 50,000 gallons of bunker oil into the bay, but no injuries on the bridge or on the ship.

That was a mere side-swipe or glancing blow -- not a head-on crash.  The Bay Bridge pylon gouged the side of the hull.  Up close the Bay Bridge pylons are rugged-looking but I doubt that they could withstand a bad direct collision.

[Jeroen3]

The regs say the ship should have steering back within 45 seconds by emergency power.
Looks like it takes more than a minute for power to recover.

These ships have massive power plants. Looks like they have four ~4 MW generators. They're big, I worked on some.
And depending on the amount of reefers they're running multiple generators are in parallel all the time. I'm not sure if they can run the main engine on emergency power alone, that is typically only to get one of the four others running.

[EEVblog]

In Tasmania they stop traffic when a large ship goes under:

[EEVblog]

The regs say the ship should have steering back within 45 seconds by emergency power.
Looks like it takes more than a minute for power to recover.
These ships have massive power plants. Looks like they have four ~4 MW generators. They're big, I worked on some.
And depending on the amount of reefers they're running multiple generators are in parallel all the time. I'm not sure if they can run the main engine on emergency power alone, that is typically only to get one of the four others running.

I heard on an interview with an expert on large ship navigation that the port thusters at full power can overload the generators and cause a complete loss of power.

[tom66]

The regs say the ship should have steering back within 45 seconds by emergency power.
Looks like it takes more than a minute for power to recover.
These ships have massive power plants. Looks like they have four ~4 MW generators. They're big, I worked on some.
And depending on the amount of reefers they're running multiple generators are in parallel all the time. I'm not sure if they can run the main engine on emergency power alone, that is typically only to get one of the four others running.

I heard on an interview with an expert on large ship navigation that the port thusters at full power can overload the generators and cause a complete loss of power.

That seems like poor design.  Surely those thrusters should be electronically limited when on emergency power, or the circuit breaker to the thrusters should trip before killing the generator too.  The last thing you need in a situation like this is losing electric power as well as steering, as it will disorient you at night.

[Jeroen3]

The regs say the ship should have steering back within 45 seconds by emergency power.
Looks like it takes more than a minute for power to recover.
These ships have massive power plants. Looks like they have four ~4 MW generators. They're big, I worked on some.
And depending on the amount of reefers they're running multiple generators are in parallel all the time. I'm not sure if they can run the main engine on emergency power alone, that is typically only to get one of the four others running.

I heard on an interview with an expert on large ship navigation that the port thusters at full power can overload the generators and cause a complete loss of power.

Yes, to operate thruster they will need more than 1 generator, often 3. Thrusters are awful for generators. They can take all the load in several seconds, and then also dump it. Wiki says the thruster is 3000 kW. That's challenging.

[dietert1]

Maybe the reason for the curve the ship took was trying to run it into the dolphins. It's terrible the ship passed all the dolphins and got stuck exactly at the bridge pillar. The pillar should have been in the "shadow" of the dolphins.

Regards, Dieter

[soldar]

Maybe the reason for the curve the ship took was trying to run it into the dolphins. It's terrible the ship passed all the dolphins and got stuck exactly at the bridge pillar. The pillar should have been in the "shadow" of the dolphins.

Regards, Dieter

What? This makes no sense at all.

There were no dolphins.

The ship was out of control. If they had any control they would have gone under the bridge.

[bdunham7]

There were no dolphins.

There are, visible here in Bing maps and in my earlier photo.  Oddly they aren't visible in Google maps satellite view.

[ejeffrey]

That would be my guess as well.
Engineering is the art of practical compromise.

Also the size of container ships has probably increased since the bridge was designed.  It doesn't sound like the bridge was designed to take a large direct impact in any case but even if it was designed for a typical ship from the 60s and 70s, it might not have been enough.  You try to plan ahead when you design a major civil engineering project but you can't necessarily plan for every thing that could happen in 50 years.

[fourfathom]

Any info on how the steering system of the ship works? I'm surprised it doesn't have enough redundancy to prevent this, in particular a backup turbine (analogous to the RAT on an aircraft) powered by the momentum of the ship itself.

On any vessel with a rudder, there needs to be water flowing past the rudder for steerage.  At low speeds, this flow is provided by the propeller.  Once that flow diminishes the rudder becomes ineffective (especially with the relatively small rudders you find on large ships).  And if you are trying to back up, a working propeller can no longer force water over the rudder, making steering even more difficult.  In this case you get "prop walk" caused by the asymmetrical water flow around the propellor (the top side is close to the hull, the bottom side is not), and this pushes the stern sideways more than the rudder can compensate for.  I believe we saw this in the video.  Also, apparently they were dragging an anchor (ships anchors are generally too small to be of much use in this type of situation), and this also made any rudder steering control much less effective.

Some ships have propellers on steerable pods, bow and stern, and/or bow and stern thrusters (mounted for sideways maneuvering thrust) but I understand that this ship only had one propeller (screw) and a rudder.

[switchabl]

Some ships have propellers on steerable pods, bow and stern, and/or bow and stern thrusters (mounted for sideways maneuvering thrust) but I understand that this ship only had one propeller (screw) and a rudder.

As well as a single 3000 kW bow thruster according to Wikipedia.
https://en.wikipedia.org/wiki/MV_Dali#Description

Not likely to have any relevant effect at 8 kts though.

[fourfathom]

Some ships have propellers on steerable pods, bow and stern, and/or bow and stern thrusters (mounted for sideways maneuvering thrust) but I understand that this ship only had one propeller (screw) and a rudder.

As well as a single 3000 kW bow thruster according to Wikipedia.
https://en.wikipedia.org/wiki/MV_Dali#Description

Not likely to have any relevant effect at 8 kts though.

I was not aware of the bow thruster -- should have checked first.  Thanks!