Comment by jlmorton | Hacker News Reader

Comment by jlmorton | Hacker News Reader

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Interesting. When the disaster first unfolded, a lot of experts came out to say the bridge appeared to lack protective barriers to help absorb the energy from a ship impact. [1]

However, the NTSB says the bridge did have these barriers. There were large protective "dolphins" directly in front of the bridge piers, but the ship managed to careen in between them at an angle, missing them, but still hitting the bridge.

In addition, there were large protective barriers surround the bridge pier that was struck:

> In addition to the dolphins, pier nos. 17 and 18 were each surrounded by a 100-foot-by- 84.5-foot crushable concrete box and timber fender system , as seen in figure 12. These systems were comprised of hollow, thin-walled , concrete box structures attached to the piers. The timber portions of the fender were attached to the outer face of the concrete box and utilized a combination of vertical and horizontal members. Additionally, steel plates were secured at the base of the vertical timber members.

[1] https://www.nytimes.com/2024/03/26/us/baltimore-key-bridge-s...

When the bridge was originally constructed the concept of such protective impact barriers was quite new. The ship is also very different from the comparatively snub-nosed envisioned C7 types, trans-Atlantic cruisers, and barges that would've gone through when the bridge was designed in 1972. Cargo ships entering the harbour used to have wider bows with a shallower draft of thirty to thirty eight feet with a very shallow prow overhang because they were built for Atlantic voyages only.

There's few barges going through the harbour these days, and cargo ships now are global and mostly built to the variety of post-Panamax standards making them extremely long with a very deep draft of forty five feet or more. That means the spacing and height originally thought to be needed to deflect barges and C7s was far too broad and short for the Neo Panamax II class MV Dali or any other modern cargo ship, and the deep draft that required a narrow bow and long prow allowed the bow to slide right in between the barriers and then ride up until it hit the bridge support. Essentially the nose had an overhang long enough that it hit the bridge support long before the rest of the ship hit the protective barrier.

I’m no expert but looking at the pictures it is clear that most of the collision took place in the air well above the water, where the prow of the ship hit the top part of pier 17 causing it to collapse onto the bow of the ship. To me, the protective barrier around the pier at the water level should have stood off much farther laterally from the pier to prevent that kind of prow contact - but then it would have blocked much of the navigation channel. Therefore the bridge should have been torn down and redesigned to modern ship dimensions long ago.

I think these barriers are designed to protect against much smaller ships.

For big ships, the ship is expected to have sufficient redundant systems and assisting tugs to not crash.

That may be the case, but such assumptions have not been justified for some time (the report says the tugs were let go on entering the channel, which it calls standard procedure.) As I noted elsewhere, more recent structures in the vicinity have been given what looks like much more substantial protection.

What is the point of the tugs if they don't take it through the part where it's most critical to have a tug?

That is a fair question, and I would guess that there are at least two different issues in play.

The first is that the ship probably has little or no ability to steer until it is moving at a few knots (depending on whether it has thrusters; I suspect not.) Once it was moving down the channel, it could steer (assuming the steering gear worked, of course.)

The second is probably that no-one with the relevant authority realized how vulnerable the bridge was to the much larger ships that have come into service since it was built (yet someone apparently realized that the adjacent power transmission towers needed better protection; sometimes people are not good at connecting the dots.)

Oh I am sure someone connected the dots, just that no politician wants to spend $bil on infrastructure if they won’t take the blame personally for an immense failure like this

That sounds analogous to what happens in software when X is designed for one thing, then a bunch of interfacing components Y & Z are changed but X isn't updated to accommodate the new edge cases.

While it is true that some protective elements existed, it is not as if this collision was a result of an unforeseeable chain of events that found a loophole in an otherwise impenetrable defense. Why were the dolphins placed so far apart, and the crushable barriers so close to the bridge piers? At some point, towers to support electric transmission lines across the channel were erected close to the bridge, and they were surrounded by barriers with a much greater radius (though I do not know if they are enough to stop the MV Dali, let alone the largest ships using the port.)

https://maps.app.goo.gl/FQCsXqomTNHShzP67

Here are two other NY Times articles, one describing a collision in 1980 by a ship half the length and with about an order of magnitude less capacity than the Dali, and another comparing (unfavorably) the protection of the Francis Scott Key bridge with that around others.

https://www.nytimes.com/2024/03/28/us/baltimore-bridge-ship-...

https://www.nytimes.com/interactive/2024/03/27/us/key-bridge...

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