Favourite quote:
Sailors talk about hydrodynamics the way CEOs talk about macroeconomics: they either treat it with mystical reverence, or they claim to understand it and are wrong. Unlike with macroeconomics, though, if you know what you’re doing you can test the propositions of hydrodynamics on actual, physical models in a lab. As in: you build little boats and then you drag them through the water, in a towing tank. Hydrodynamics is what a five-year old would do, if a five-year old had a PhD.
Even in the 1980s the Fed under Paul Volcker tried to reign in inflation too quickly, causing a recession.
Also I have seen pictures of the bow but none of the stern. What’s the situation there? It sounds like the riprap might need to be cleared out on both ends before the ship can be moved out of the way.
With respect, I don't think that it is a case of that being wrong or right. The article posits that there is a lack of understanding about hydrodynamics in shallow water.
> ... hydrodynamics in shallow water are different. When a boat moves through the water, it pushes the water out of the way — it displaces it. “Where the water needs to be displaced, in a deep ocean it can go under the ship and that’s not a problem,” says Lataire. “But if it needs to go into shallow water, like the Suez, the water simply cannot go under and around.”
> The Suez Canal is basically just a 24m-deep ditch dug in the ground to let the ocean in. When a ship comes by and displaces the water, the water has nowhere to go; it gets squeezed in between the ship’s hull and the floor and the sides of the ditch. A ship in a canal can squat, for example — it can dig its stern into the water. When water gets squeezed between a ship’s hull and a sand floor, it speeds up. As water flow speeds up, its pressure drops, pulling the hull down to fill the vacuum. The effect is more pronounced at the stern, and so the ship settles into a squat: bow up, stern down.
> ... Lataire wrote his dissertation on a similar phenomenon as a ship passes close to a bank: the bank effect. The water speeds up, the pressure drops, the stern pulls into the bank and, particularly in shallow water, the bow gets pushed away. Stern one way, bow the other. A boat that had been steaming is suddenly spinning.
> Most of the research and design on ship hulls goes into efficiency and stability at sea. But at sea is not where the Ever Given got stuck. And ships have gotten big, fast, which means the consequences of shallow-water hydrodynamics are changing by the year.
Anyhow, the article argues gently that big ships are being built with scant regards for hydrodynamics in shallow waters, and it makes a case for some proper research before building more.
As far as the larger point of the article/last paragraph, I couldn’t agree more. We keep taking up more space and using more resources while the plant stays the same size. It’s not sustainable. Maybe we need to stop shipping so much stuff around since let’s face it a decent amount of it is useless consumer junk. I can also see us building ships so large that they don’t go to ports but rather get unloaded onto smaller ships off shore, similar to how a planet to planet spacecraft might not be able to land/take off but only go between orbital stations.
doesn't seem so :
https://en.wikipedia.org/wiki/Squat_effect
"The third largest cruise ship in the world, MS Oasis of the Seas, used this effect to obtain an extra margin of clearance between the vessel and the Great Belt bridge, Denmark, 1 November 2009, on a voyage from the shipyard in Turku, Finland to Florida, USA.[5] The new cruise liner passed under the bridge at 20 knots (37 km/h) in the shallow channel, giving the ship extra clearance due to a 30 cm squat."
The current situation with EverGiven seems to be more like a ship piloting error - as normally they are taught about the Bernoulli based bank/squat effects when piloting near ground or near other ships moving in parallel direction.
(I wanted to credit the person who posted it yesterday, but can't find him/her)
edit: better one https://youtu.be/oWF7A9Ujr3w
One suspects the only thing that would have prevented this disaster is if they pilot had put it into full reverse when the wind stopped pushing it. There is so much momentum on these things it would continue to go forward, but it would have a force vector in reverse that was applying (perhaps successfully, perhaps not) a counter torque to the direction of travel.
Another artifact of traditional (non-azimuth) propeller driven ships in reverse is that they have very little steering control if they are moving slowly as steering requires water moving over the rudder. In forward water is actively being pushed over the rudder due to its position behind the prop, but in reverse this flow is not as strong.
But I couldn't help but thinking about the future effects of global warming, specifically gusting winds, and wondering if we're going to see this kind of jamming of the Suez more and more frequently.
http://investorsnewsblog.com/2021/03/25/the-bank-effect-and-...
> Why do I have to complete a CAPTCHA? Completing the CAPTCHA proves you are a human and gives you temporary access to the web property.
No kidding. But why?
I tell people to steer sooner and more slowly than they think they should because "swerving" to miss something isn't really a thing. You just crash.
And flying behind/below things is easier. The second you get up above the tree line or from behind that building where there's real wind, it's 10x harder.
Yet another article that needlessly complicated things by invoking the Bernoulli principle. It’s a lot simpler to explain: the space behind the stern needs to suck water into it so the stern area is at lower pressure, while the space around the bow needs to push water out of the way so it’s at higher pressure. The closer you are to the sea floor or bank, the bigger the effect since there isn’t much space to push water away and pull water from.
The bow moves water out of the way when it moves forward and the stern vacates space which the water fills. So water is going away from the bow (positive pressure) but towards the stern (negative pressure).
When a ship travels, water moves from the front to the back — and this shifting the water creates pressure as the water moves (which is also where drag comes from).
If the water only has a narrow space to move, it has to move faster through that area, so the pressure is higher/lower. (Higher before where it bunches up on the bow, lower after where it rushes to fill behind the stern.)
If one side has more space than the other (eg, left has less space) the the water goes faster on that side and so the pressures on that side are more extreme (eg, pushing the left bow rightward and sucking the left stern leftward — turning the ship right).
That is, the normal front-to-back pressure can cause a twisting force if the flow isn’t balanced left-to-right. Because the side with less flow ends up with water bunching up at the front and not enough in the back.
The Mississippi probably a more complex environment than the Suez Canal given the significant number of turns and strong currents but I'm somewhat surprised there isn't something similar there in Egypt as it seems like a narrow passage.
I’m curious what the solution will be, but I’m most disappointed about the lack of photos, videos, reports about what is broken (it’s taking in water ; did it have an electrical breakdown? why did it draw a d... before entering the canal? pilot immaturity?).
I guess it’s a side-effect of being ashore far away from population. We’re pretty much left with 2 images of a digger, a satellite, and no public communication from the Smit Savage company (who’s in charge of the multimillion salvage). Not all the world is covered with handheld reporters, finally!
Do most HN users have one or more accounts to sites like this?
That's about what the current publishing sector take is now.
And no, to pre-empt it the mythical "micropayments" solution isn't going to replace either.
