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Baltimore's Key Bridge struck by cargo ship, collapses

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Re: Baltimore's Key Bridge struck by cargo ship, collapses

#981

Post by pixl97 »

OJFord wrote: post #783
pixl97 wrote: post #687

Earlier quoted context omitted.

Ya the people on the bridge would have less than 4 minutes to figure out the ship is crashing then to clear 2500 feet of bridge. When you're working with construction equipment you'd probably not notice till you had seconds left.

4 minutes is a lot longer to save your life than nothing? And do you really think that's the answer, that was the calculation on the ship - well they only have 4 minutes until we hit anyway, so there's nothing they can do, not worth it? I wasn't criticising anyone, I was 1) asking if that happened; 2) asking why it might not have. I think the answer is much more likely that the loss of power disabled the horn (as oth…

So, it turns out they did call in an emergency and the police did shutdown the bridge. The police had no direct way of reaching the workers and weren't going to wander out there with an imminent impact. So, evidently, no there was not enough time.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#982

Post by histriosum »

efitz wrote: post #786
Arrath wrote: post #739

Earlier quoted context omitted.

It seems much more reasonable to only disengage the tugboats that were already helping the container ship get under way once it clears navigation hazards like the bridge, instead of keeping 24/7 quick-response tugboats at the bridge that try to intercept an out of control ship in a bare few minutes.

Moving large boats across water is slow. The Francis Scott Key bridge was 8600 feet long, or 1.4 nautical miles. AFAICT there were just over 4 minutes from the time that the first power outage started until the ship struck the piling. A modern harbor tugboat can go perhaps 15 knots. In 4 minutes this means it would travel 4 nautical miles, at the very best (running start in correct direction). So let's say that there…

> A modern harbor tugboat can go perhaps 15 knots. In 4 minutes this means it would travel 4 nautical miles, at the very best (running start in correct direction).

It's probably pedantic, but I don't understand your math. Knots are nautical miles per hour. To travel 4nm in 4 minutes would imply a speed of 60 knots. At 15 knots, you would travel 1 nautical mile in 4 minutes. (15kn/60min * 4min = 1)

Or it's possible I haven't had enough coffee.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#983

Post by 16bytes »

ProllyInfamous wrote: post #876
16bytes wrote: post #761

Earlier quoted context omitted.

There is already something like this in use: harbor pilots, who have specialized knowledge of specific ports and board vessels to navigate them through critical transit zones. It is reported that there were pilots on board navigating at the time of the collision. Tugs are used in tight locations, but they can only change a ship's speed at a very slow rate compared to that ship's engines. By analogy, you can pull a tr…

I feel that in this situation a nearby tug boat could have diverted the ship (by at least kept it from straying from the shipping channel during power failure).

I think you're probably right. A tug (or two) hypothetically could've provided some emergency directional control.

When they reopen the port, it'll be interesting to see what early mitigations they put in place.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#984

Post by topspin »

DennisP wrote: post #745
scoot wrote: post #661

Earlier quoted context omitted.

Even compared to the economic impact of a bridge collapse and resulting port closure?

Yeah I'm guessing just replacing the bridge will cost a lot more than the bumpers would have, even without counting the broader impacts.

Supposedly "state officials" shot down bumpers on cost. They made a bet and it turns out that they've won: Biden has committed to paying the entire cost of replacement[1]. Instead of investing in bridge defense to protect a 50 year old bridge and its ever increasing maintenance costs they get a brand new bridge for free!

[1] "It is my intention that the federal government will pay for the entire cost of reconstructing that bridge, and I expect the Congress to support my effort"

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#985

Post by acdha »

berniedurfee wrote: post #902
acdha wrote: post #856

Earlier quoted context omitted.

The early reports suggest that the ship was having trouble actively maintaining position - some have theorized a stuck rudder or wind pressure – in which case the only thing an autopilot could do is make the situation worse. I’d wait for the full investigation to come out before speculating about fixes.

Not a fix per se, but a safer system going forward. Given all the variables, is it feasible to build a system that continuously runs through multiple failure modes, predicts where the ship would end up and then guide the ship on a course where even a loss of power would have the ship drift between the supports. Was there a configuration of the ship that would have prevented it from hitting the bridge even after the p…

> guide the ship on a course where even a loss of power would have the ship drift between the supports.

If one of the failure modes is a stuck rudder, how’s that supposed to work in a narrow space where it could be drifting in either direction?

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#986

Post by nwiswell »

ViewTrick1002 wrote: post #943
nwiswell wrote: post #751

Earlier quoted context omitted.

The sheet piling didn't need to be 50 years old. In 1977 (and in 1972, when construction began), vessels of this size did not exist, and certainly were not allowed in the harbor[1]. But over time, they were given authorization, despite the fact that they could collapse the unprotected bridge like a load of toothpicks. The real crime here is that there was no retrofit to protect the pylons. It was almost certainly con…

The Oil Tankers of the 70s were the largest vessels ever built. Today the largest container vessels are starting to creep up to their size, but not weight. The container vessel in question is tiny compared to e.g. the Seawise giant or Batillus Class. https://en.wikipedia.org/wiki/Seawise_Giant https://en.wikipedia.org/wiki/Batillus-class_supertanker

Those ships would never have been permitted in the Baltimore harbor. They presumably still aren't, since there's no reason for them to be there.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#987

Post by efitz »

histriosum wrote: post #982
efitz wrote: post #786

Earlier quoted context omitted.

Moving large boats across water is slow. The Francis Scott Key bridge was 8600 feet long, or 1.4 nautical miles. AFAICT there were just over 4 minutes from the time that the first power outage started until the ship struck the piling. A modern harbor tugboat can go perhaps 15 knots. In 4 minutes this means it would travel 4 nautical miles, at the very best (running start in correct direction). So let's say that there…

> A modern harbor tugboat can go perhaps 15 knots. In 4 minutes this means it would travel 4 nautical miles, at the very best (running start in correct direction). It's probably pedantic, but I don't understand your math. Knots are nautical miles per hour. To travel 4nm in 4 minutes would imply a speed of 60 knots. At 15 knots, you would travel 1 nautical mile in 4 minutes. (15kn/60min * 4min = 1) Or it's possible I…

I made a math error but couldn’t correct it after I had votes - 15kts for 4min = 1 nm.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#988

Post by ithkuil »

amluto wrote: post #957
ithkuil wrote: post #816

Earlier quoted context omitted.

If you're moored on the ground you'd be torn apart in both cases

On the other hand, if I were hit by a loaded shopping cart at 3 mph and I weren’t allowed to move my feet, I’d probably be okay if I saw it coming. Keep the same momentum but scale the mass down to, say, 200g. Now it’s supersonic, and it will hit with maybe 10x the energy of a musket ball. This would be extremely damaging and likely lethal. (If you make the mass too small, it might go straight through a person, in wh…

But the point was that if you were hit with a full container ship at 0.1 mph and not allowed to move you'd be dead.

The only reason why a high energy but slow moving object (thus high momentum) is harmless is that it will deliver a small acceleration to you and you won't suffer from the consequences of a high acceleration (which is what generally kills people when they hit something like the ground at high speeds). But that assumes that you're free to be accelerated and move away.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#990

Post by jaxson60 »

varrock wrote: post #903
naasking wrote: post #839

Earlier quoted context omitted.

Indeed, the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material, which means the whole bridge bent until the deflection exceeded the tensile strength of the material. A missile impact with the same total energy would exceed impact strength and would probably have destroyed only part of the bridge.

Thank you for breaking it down like this. As someone without an engineering background, your explanation (along with some Googling for terms and definitions) really helped me grasp what happened. You got me wondering: > the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material When I first read this, it initially threw me off. The cargo ship's impact not exceeding the stren…

Bridges were not designed for being hit. They were designed to span. If those designing and engineering it had considered an impact, the design would not be catastrophic but rather sectional. If sectional, each span would remain standing rather than collapse like dominoes. It takes 3 miles to stop a 100k ton stacked container ship. The things nobody has mentioned are: Current direction and speed. Wind direction and speed. The entry of the vessel in relation to the bridge. The fact that dragging anchor would have on the starboard side pulled the bow right into the pilon, the worst case.
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