[HN Gopher] The bank effect and the big boat blocking the Suez
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The bank effect and the big boat blocking the Suez
Author : connorlu
Score : 90 points
Date : 2021-03-25 23:16 UTC (23 hours ago)
(HTM) web link (www.ft.com)
(TXT) w3m dump (www.ft.com)
| caseysoftware wrote:
| I've taught a ton of people to fly RC helicopters and drones and
| the physics of it _is_ the hardest part. The lack of friction
| throws off our sense of control.
|
| 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.
| neonate wrote:
| https://archive.is/pmUEm
| burlesona wrote:
| It is infuriating that archive captchas are positioned
| offscreen on mobile and therefore can't be solved.
| samizdis wrote:
| You might try this link, which I got via a DDG search and
| which _seems_ to be the complete article:
|
| http://investorsnewsblog.com/2021/03/25/the-bank-effect-
| and-...
| kristianp wrote:
| Interesting, I've never seen a captcha on archive.is. I'm on
| Android on wifi.
| [deleted]
| jp57 wrote:
| It is infuriating to have to solve a captcha just to see a
| page.
|
| > 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?
| sn_master wrote:
| To avoid DDoS and content scrapers that would harvest the
| article text and put it on link farms to get clicks from
| confused search engines.
| cwwc wrote:
| If ya go portrait mode on Safari you can access
| ummonk wrote:
| _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._
|
| 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.
| simonh wrote:
| Why do they need to be at higher or lower pressure? That
| doesn't explain anything.
| JxLS-cpgbe0 wrote:
| Your explanation is longer and harder to understand. (How do
| you "invoke" Bernoulli's principle?)
| [deleted]
| IgorPartola wrote:
| In other words it was going north, wind was blowing from the
| West. To correct, the ship was steering a bit to the left to
| compensate and have the whole ship go forward. Then suddenly the
| wind stopped, the bow got too close to the left/West bank, and
| the bank effect repelled it swinging it to the right. Once the
| bow got stuck, the stern got stuck on the left as it kept going
| forward and the ship spun clockwise. Do I have that right?
|
| 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.
| samizdis wrote:
| > Do I have that right?
|
| 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.
| trhway wrote:
| >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.
|
| 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.
| m463 wrote:
| Watching this timelapse of the canal transit it you can see all
| the forces and corrections that happen, and coupled with the
| lenght, mass and momentum, I'm surprised they don't have more
| of these events.
|
| https://youtu.be/L0J-VIvKLsc
|
| (I wanted to credit the person who posted it yesterday, but
| can't find him/her)
|
| edit: better one https://youtu.be/oWF7A9Ujr3w
| more_corn wrote:
| If you keep posting paywalled articles paywalls will persist. If
| you ignore them all they will cease to be relevant and they will
| die. Vote with your attention for the future you want.
| mprev wrote:
| If we insist on not paying for journalism then what little
| quality journalism we have left will die. Vote with your wallet
| if you want a future that isn't just listicles and manufactured
| outrage.
| [deleted]
| simonh wrote:
| Alternatively if more people paid for valuable services by
| skilled professionals that cost a lot to provide, the service
| would be better funded and/or could be cheaper for everyone.
| [deleted]
| [deleted]
| chrisbaker98 wrote:
| Stick the link into archive.is and paywalls are trivial to
| circumvent.
| jefft255 wrote:
| The future I want includes competent journalists being paid and
| websites that aren't filled by garbage ads and nagging. Not
| saying paywalls are nice, but what is the future _you_ want?
| edoceo wrote:
| By what method should we/you compensate the journalist if not
| subscription, paywall or ads?
| kruxigt wrote:
| Micro transactions is a model that might be a good
| alternative to all of those. The idea is that if you agree
| on paying say 1 dollar you get to access that specific
| article. There can of course be variations like you pay x
| to get future access to y number of articles.
| chrisbaker98 wrote:
| Something involving NFTs, I guess.
| dredmorbius wrote:
| Subscriptions rolled into broadband/mobile at $120/yr US net,
| tiered by local prevailing wealth, and pro-rated based on
| estimated access seems a good start.
|
| That's about what the current publishing sector take is now.
| colinmhayes wrote:
| I prefer to pay for the services I actually use, not let
| someone else choose for me.
| josefresco wrote:
| A subscription to FT.com costs $372 for 1 year.
| hu3 wrote:
| That's.... a lot.
| [deleted]
| [deleted]
| dageshi wrote:
| So you're saying we should avoid paywalled content,
| irrespective of how good it is and encourage ad supported
| content instead because those are the only two real
| alternatives.
|
| And no, to pre-empt it the mythical "micropayments" solution
| isn't going to replace either.
| rossdavidh wrote:
| My goodness, that was odd. I just read a news article, and yet I
| feel better informed about something.
| disgruntledphd2 wrote:
| The FT is expensive, but well worth it (it's good _because_ it
| 's expensive, as journalism is).
| andrepd wrote:
| They have their own biases, but at least they're very good
| when read in combination with other sources.
| dgritsko wrote:
| I learned the term "riprap" from this article. I've seen plenty
| of examples in person, I just never knew it had a specific name.
| https://en.wikipedia.org/wiki/Riprap
| dnautics wrote:
| if you ever have the chance to visit new orleans, there is a turn
| in the river near the public boardwalk and it is simply amazing
| to watch giant ships (though not nearly as big as the evergreens)
| take a drifting bank through that turn at what looks like 15 kts,
| maybe more.
| samizdis wrote:
| What a terrific article, certainly the only one I've seen to look
| at the science of this - and to point out that the ship didn't
| just hit sand: that section of the canal is lined - it went
| through "protective" boulders to reach that sand.
|
| 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._
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(page generated 2021-03-26 23:01 UTC)