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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

#921

Post by ropable »

paddy_m wrote: post #438

Youtube tracking analysis from a knowledgeable mariner. He says that at about 1:24 AM the ship loses power (from video feed) while traveling 8.5 knots. at 1:25.30 power is restored. at 12:25.59 the ship shows smoke. The ship has already drifted in the channel. It is believed that at this time the ship applied full reverse power as evidenced by the black smoke. (My analysis: the ship drifted but hasn't turned in the c…

It's fairly horrifying how fast the bridge collapsed after the moment of impact on the pylon. The whole span seemed to fall in totality almost at once. If anyone was on that bridge at the moment of impact, they were in the water a couple of seconds later.

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

#922

Post by sho »

snarkconjecture wrote: post #915
sho wrote: post #909

Earlier quoted context omitted.

Hm. I'm no physicist but I think your math is off. Remember it's velocity squared. Your car going that fast is has more than a kiloton of TNT or approaching 5 terajoules of energy... that can't be right. For a 2 tonne car, my very rough math puts it at more like 2100 mph.

Momentum is just mv, not mv².

I can't edit my post now, but to be clear I was talking about kinetic energy. I would have thought momentum is not a very useful thing to talk about in a case like this where there was some pretty obvious transformation of energy into damage, etc.

As I said though, I'm far from a physicist so happy to be schooled if I'm way off...

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

#923

Post by hanche »

jml78 wrote: post #813
paddy_m wrote: post #574

Earlier quoted context omitted.

To anyone reading this who isn't an experienced boater: If you are invited onto someone else's boat, sit down and shut up during docking, don't talk to friends, let the captain concentrate. Don't help, if the captain wants you to do something, they will let you know. If you think you know better than the captain, and this advice is unknown to you, you don't know better. Being a good guest during docking shows experie…

Take things slow so you aren’t the show. I have a 44ft sailboat. Docking is not easy. People do not realize how difficult it can be

Try docking a sailboat on a river. Then slow isn’t an option, since the current will sweep you away in a heartbeat. The key here is planning ahead, including a plan for what to do when you don’t get it right. And you won’t, on the first couple of attempts. I’ve seen it in action, totally hair raising to watch.

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

#924

Post by wolverine876 »

ultrarunner wrote: post #557
paddy_m wrote: post #438

Youtube tracking analysis from a knowledgeable mariner. He says that at about 1:24 AM the ship loses power (from video feed) while traveling 8.5 knots. at 1:25.30 power is restored. at 12:25.59 the ship shows smoke. The ship has already drifted in the channel. It is believed that at this time the ship applied full reverse power as evidenced by the black smoke. (My analysis: the ship drifted but hasn't turned in the c…

I'm once again impressed that subject matter experts are out there on every topic, and they are often capable of quickly and accurately disseminating information about an event far better than the local news.

I don't know about local news, but other news sources interview lots of those experts.

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

#925

Post by eternauta3k »

throw0101b wrote: post #551
danpalmer wrote: post #501

Earlier quoted context omitted.

It's somewhat counterintuitive how much energy can be in something moving so slowly. I say somewhat, because when you're up close it's much more obvious, but you're right that on a video it doesn't look like much.

> It's somewhat counterintuitive how much energy can be in something moving so slowly. Reminder: Kinetic Energy = ½mv^2 Squaring numbers can make them big in a hurry.

Nitpick: squaring makes numbers greater than 1 bigger, and numbers smaller than 1 smaller. In this case we're squaring something with units, and we can't say the input is greater or smaller than the output, because they have different units. What we can say, is that v^2 curves upward: it grows faster with increasing v, and slower with decreasing v.

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

#926

Post by reliablereason »

IG_Semmelweiss wrote: post #213

Also important to note. The logistic company running this ship was Maersk. That is the same shipping company that had the ever given stuck in the suez canal a few years ago. Is Maersk now officially the "Boeing" of shipping?

No, with the top reason as to why not being that Maersk did not construct the ship.

Saying that Maersk is at blame is like blaming the airline instead of Boeing.. if you want to make that parallel.

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

#927

Post by somenameforme »

hanche wrote: post #920
somenameforme wrote: post #899

Earlier quoted context omitted.

Quite amazing videos. I've no experience in this domain and so it makes me immediately wonder - is there no risk of substantial damage from those ships colliding due to a wave hitting e.g. the smaller ship just right and pushing it hard against the larger one?

I am not an expert, but clearly pilot boats must be built to take a lot of punishment. And they don’t have the mass to damage the big ship beyond the paint layer.

I agree that it seems that must be the case. I'm just curious where my assumptions break down - whether I'm overestimating the mass of the pilot boat, overestimating the force a single perfect wave can impose, or underestimating the thickness of these ships' hulls.

I've just always be impressed by the amount of energy that boats impart when they collide with anything. Like in this case, the entire bridge was brought down by a collision at under 8knots. Obviously that ship had orders of magnitude greater mass than the little pilot boat, but presumably you want to avoid even dinging up the larger ship, and so that's an orders of magnitude smaller goal as well.

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

#929

Post by shiroiushi »

toss1 wrote: post #398
rpeden wrote: post #153

Earlier quoted context omitted.

Because the Port of Baltimore is a very major port, and not allowing ships under it really isn't an option. Vertical clearance for ship traffic might have been the reason this kind of bridge was built in the first place. Otherwise, something lower and more causeway-like might have been sufficient.

>>Because the Port of Baltimore is a very major port, and not allowing ships under it really isn't an option. It is now a very large port that is completely closed off from the sea. And two sides of the city no longer linked The damage from this accident is only beginning. Even if loss of control of a large container ship was considered in the design of the city, port, and that particular bridge, ships were not even…

>And two sides of the city no longer linked

Have you looked at a map of Baltimore? They're very much linked, you just have to drive a little farther. The only issue will be that all the traffic this bridge previously carried now has to reroute to the bridge farther north, so now traffic will be much heavier.

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

#930

Post by TaylorAlexander »

archi42 wrote: post #112
TaylorAlexander wrote: post #66

Somehow I find it surprising how completely the bridge collapsed after the damage. I understand that a container ship collision is serious, but you could imagine a scenarios where the bridge slumps or buckles but doesn’t just disintegrate like that. It’s surprising that ships capable of doing this damage were probably regularly driving past it, and its safety as a thoroughfare depended entirely on those collisions no…

You could try to avoid collisions with barriers, or make the bridge fail differently (only a few spans), or make it tolerant to a single support failing. But you need a pretty beefy steel beam to survive a direct hit by... Uh... 200,000t(??) traveling even at a slow jogging pace. (And then it transfers the energy into the rest of the bridge, which will very much not like it). I guess we can be happy failure like this…

Right. I am not really thinking of designing pillars that are impossible to knock over. I am thinking of alternative bridge designs where a higher percentage of the total bridge stays up when one pillar is taken out.

On this bridge, the main section of the bridge is supported by four spaced pillars, making three main spans there. One of the middle two towers was hit, so this should affect two of the three spans. But it took down all three of them. A span that was supported on both sides by intact towers still came down. That is what I find most surprising here.

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