Why Are Big Ships Bendy?
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- Опубліковано 23 лис 2023
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✩ABOUT THIS VIDEO✩
In this video we explore hogging and sagging, and learn that it is completely normal for massive ships to bend and flex.
✩ABOUT CASUAL NAVIGATION✩
I am a former maritime navigational officer and harbour pilot, with a passion for animation. My hobby is presenting educational stories and interesting nuggets from the maritime industry and sharing them on social media to keep them freely accessible to everyone.
For training & educational use, I offer downloadable variants (free from all ads, sponsors, and social prompts) in the Casual Navigation Store: store.casualnavigation.com/
✩SUPPORTED BY PLUS MEMBERS✩
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Thank You to all Plus members on Patreon. Your support helps keep these videos freely accessible to everyone across social media.
✩WITH THANKS✩
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Pig - Shenyakot / Shutterstock.com
✩DISCLAIMER✩
All content on this channel is provided for entertainment purposes only. Although every effort has been made to ensure the content is accurate and up to date, it remains the responsibility of the viewer to determine its accuracy and validity. The content should never be used to substitute professional advice or education. - Розваги
The Little Captain is available from the Casual Navigation store:
store.casualnavigation.com
cool
2w ago
why was this comment 2 weeks ago when the video was released 2h ago?
@@user-pg1ns1tf3oMaybe it's released earlier for patreon subs or something?
@@user-pg1ns1tf3o because content creators can queue up/upload videos before they launch publicly.
Today I realized that I no longer consider myself "most people" about nautical stuff anymore because of how much this channel has taught me. I've learned a lot here.
My Father was a great lake sailor in the 1920s. One of his ships was just a few years old but nicknamed "the hunchback" due to a permanent bend in the hull from a bad storm.
Thanks
the lakes are truly ferocious, michigan doesn't have the most lighthouses in the world for a reason
@@circleinforthecube5170 Lake Superior is the scary one. Giche-gami to the Ojibwe, gitche-gummi to Gordon Lightfoot.
How old are you?
@@stefanc4520 71
That's actually how most torpedoes work nowadays : remove water from underneath the keel and let the beam sag beyond limits. Works especially fine with sub, and you don't need to be too accurate to produce massive effects (ie, even if you don't hit the target, it's likely to be damaged)
Or the reverse, lifting it up above the highpoint of the flex arc
It doesn’t remove the water, it pushes the ship up and breaks the keel, an explosion lasting a fraction of a second wouldn’t clear enough water out to cause it to snag. It gets thrusted upwards, literally snapping the keel as it comes back down. There’s UA-cam footage of Uboats sinking merchants where you can observe this
@@223frankthetank key point being nowadays. U-boats are hardly current tech, iirc
@@MrHegemonie still not how it works though. And the technology for torpedoes only changed in how they’re fused and how they track targets. An explosion under a ship is the same, whether it’s 1000 pounds of explosive from 1941 or from 1991 doesn’t change how the physics themselves interact with the ship…
Fusing and detonation were just
Worse back then. Torpedoes haven’t changed much
@@MrHegemonie do modern torpedoes explode _slower_ than WWII-era ones? 🤔
In metrology (the science and craft of measuring things), there's the saying that everything is rubber. Even solid granite measuring plates have _some_ sag when supported at the ends. The trick is to keep the deformation of your measuring setup so small that it doesn't matter for what you're measuring.
There's a video taken by a crew member during a storm on a large freighter of some type showing an unnerving, to me anyway, of the flexing of the ship in a passageway that runs the length of the ship. It's actually kind of terrifying.
I was in the merchant marines for years and watching a ship flex in heavy seas is a good thing. When they do not flex is when they crack. I was on a brand new ship 40 years ago that sank on her 2nd voyage across the Atlantic. It was determined that the steel used was too stiff.
There's a video of a ship snapping in half:
ua-cam.com/video/gaZhnNlutuQ/v-deo.html
Been there, seen that. Makes you think.
Think I've seen the same one, there are others of suspension bridges and looking vertically down elevator shafts of large towers, crazy how much flex is actually "normal" for these types of structures.
Planes are also designed to do this. It may seem spooky but your common 747 and others like it their wings can flex nearly 20 feet up or down easily
I feel like "motion of the ocean" was used in this video more than normal for this channel lol
I hear it means small craft advisories.
Hearing you say "motion in the ocean" is something I didn't know I needed in my life
I saw a vid of a Great Lakes bulk freighter hogging and sagging in a storm. Quite impressive. And scary!
You find a long hallway on a cruise ship in bad weather you can also see the hogging and sagging happen.
Put down a camera and let it record down the hallway and you can see it.
Reminder: its the motion of the ocean AND the size of the ship.
Hogging is basically what I assume happens in the Dreadnoughts song "Roll Northumbria" (fictional ending of the British supertanker Esso Northumbria; in reality she was scrapped, fearing this would happen, since she was apparently a straightforward scaled-up version of a smaller tanker with not much consideration for the behaviour of larger vessels at sea and so cracked her hull often for her short life). She rides above a rogue breaking wave, her hull can't handle the compression and the cracks finally split her open.
"-for atop a wild breaker, the cracks in her frame
spilled her black guts all across the wild main
she limped away through an ocean of flame
Roll on, Northumbria
Roll, Northumbria, roll"
Actually, would love to see a video on that ship someday.
Now for the really scary part: Metal that is repeatedly flexed back and forth experiences an effect called work hardening.
The flexed part gets harder and more brittle with every motion. Given that in a ship's hull the flexing takes part over a great length, this takes a long time to become relevant, but it inevitably will weaken the structure.
So, no matter how well you take care of your ship's hull, it's days are numberd.
It is not generally a problem for metal parts. It might be true for ships but I am not an expert on that.
With ordinary shafts for example you don't have to consider work hardening. Instead you get fatigure cracks that form due to the repeated load cycles. These fatigue cracks only form when you stay above a certain strain threshhold. If you stay below a strain threshhold the shaft will effectively withstand the load forever (of course corrosion and other physical and chemical processes can still damage the part). With ball bearings for example there is no strain threshhold. They will ultimately always die sooner or later due to the cyclic load of the ball passing through the load zone and the corresponding hertzian contact pressure in the inner ring.
Well, you could always replace these overstressed parts, and before anyone brings up the quite ironic in this scenario, what ship of Theseus problem no we are dealing with easy to repurpose metal which means we can just melt down old parts into new parts you can keep ships around for several millennia by doing this
@@FluppiLP As I'm a mechanic, not a materials engineer, my knowlege of material sience is limited, but as I see it, these fatigue cracks are a result of work hardening. Work hardening happens where a piece of metal is deformed past its limits for elastic deformation an enters the realm of plastic deformation (the strain threshold you mentioned). Quite often, you will find a combination of both eleastic and plastic deformation - unless you overengineer a work piece to a certain extent. In this case, the cracks will start slowly in those parts that did experience plastic deformation, slowly increasing the load on those parts that so far only experienced elestic deformation.
If you make totaly sure your work piece will only ever experience elastic deformation, then you should be safe from work hardening and fatigue cracks. That works if the loads your piece experiences are reliably calulable. Like in a shaft for a stationary engine driving a generator.
But if you have something that moves through the environment, you will encounter shock loads and similar issues. Like a ship's hull steaming through a storm.
It depends on the material. Aluminum will do that, steel won't weaken from repeated stress if it's under its safe limits.
@@HeatherthefurryIrishRedSoxfan The problem with this is, that a) this load is spread over a large part of the hull, thus you'll have to replace a large part of the hull and b) those parts are very much integral to the hull's basic structure. So, you'll be looking at a major rebuild. If you factor in everything else that can and will deteriorate and needs to be replaced, you will end up with a bill that comes close to what a new ship will cost.
If you ever get to go on such a ship in bad weather and look down a long corridor, you'll see the length of the corridor flex up and down, and a little side to side. It's pretty unnerving the first time you experience it, but is a cool phenomenon.
'little captain' and 'motion of the ocean'
for a second I thought this video was going to go from nautical to naughty
This was an issue with the early liberty ships where the prefabricated sections were welded together but sadly poor construction tolerances lead to the keel sections and other strength members not always lining up at the adjoining bulkheads which you can imagine reduced overall hull strength considerably. Couple this with poorly normalised steels and welding temperature control issues along with cold Atlantic waters and you had a fatigue nightmare. The construction tolerance issue was quite difficult to eliminate and examples appeared well into post war decades worsening as overall hull dimensions increased with bulk carriers.
Great content as always! Thanks!
Great video man!
Thx for another fascinating video. Just wondering if you are keeping abreast of the changes being trialled on cargo ships (wind wings, methanol, batteries etc) and it would be interesting to hear if any of these changes are presenting extra challenges for the captain and crew. Keep up the great work 😀👍
This comes up in drilling pipe and tubing imported from overseas because the long sections can be weaker than expected from flexing during travel.
Thanks for sharing another great video.
And the hogs belly sags, a bit like mine! lol. Seriously though, my respect goes out to the crews of container ships. What a complex job they have on their hands, travelling the worlds waterways so we can all get our goods without any appreciation or even a second thought.
Diggin’ the new ocean waves graphic 🤗
Love this channel
1: it's a fysical object. everything bends.
2: "i mean we can make it bend less? but trust me it'll snap in half like 100x more often"
Is there a potential video in the Marco Polo grounding in Swedens coastal band, perhaps with how modern cruise ships navigate in archipelago?
The motion of the ocean 🗣🗣🗣🗣🔥🔥🔥🔥🔥
Lack of buoyancy is what many think is what killed the Mighty Fitz. Random/rogue waves on Lake Superior caught her between crests and the lack of support snapped her in half.
How about cruise ships?
The new modern ones (check out Adam Savages series) can have a staggering amount of people, moving about an congregating depending on activities.
Is this something that would be taking into account when designing hull and internal layout?
People weigh nothing compared to the overall size of the ship. The Wonder of the Seas has a gross tonnage of almost 237.000t. Comparatively, her deadweight tonnage is 17.100t. At maximum capacity, crew and passengers take up about 750t of that. That's not a lot stability wise. Compare this to the largest cargo ship. Gross tonnage is 236.000t, but summer deadweight is 241.000t(according to Marinetraffic). Hogging and sagging in cruise ships has much more to do with the weight and design of the ship than by what is loaded.
Yes, I can't remember the exact criteria but it has something to do with how much the ship is allowed to list to one side if all passengers go to that side, I think there are some additional requirements for passengers ships compared to cargo ships.
It has to do with Gm curves and intact stability etc, I have luckily forgotten all about it.
What a great channel. Keep it up
Good video. Makes sense.
The little captain looks great
When is the next live stream? It was suuuper chill :)
That captain plush is so cute
Ships also twist in torsion between bow and stern. The cargo masts on a tanker can be seen to align, then spread laterally, then realign as the ship twists as it moves through and over a wave.
Great work, i just wish your videos were longer
When calculating ships seaworthiness and draft you figure out several variables. Draft and trim is obvious but also the vessels stability The stability is defined by the distance between the meta center and the center of gravity (GM). We also used to calculate on what angle of list the vessel would capsize. In addition we would calculate structural conditions like hog and sag. In addition you also have the shear forces that also have to be taken into the equation. On every ship the limits for hog and sag and for shear forces are clearly defined. One for port conditions and one for seagoing. The limitations for seagoing are naturally stricter. Before the days of computers you had to calculate this by hand but there were devices that could help you speed up the process. On the devices you set the weights and the device would in a clever way tell you if you were within the limits.
Here I was all my life thinking the sea was boring & shipping was stupid…
3 videos in I’m hooked 😅
THIS IS WHY THE FRONT FELL OFF
The little captain is adorable.
there is a stress value for steel that if you stay below that it can flex forever . i have large hydraulic presses. the tierods are usually prestressed to 10,000 psi. at that level they will last forever regardless of cycles . we have a press from 1939 still working . it must have millions of cycles on it
My sisters bf has as a engineer/mechanic on a EEE and talked about the halfway from the superstructure to the engine room visible moving
*Question 1: **_What are most springs made out of?_*
*Question 2: **_What are cargo ships made out of?_*
*???*
🤔
I got this notion that the motion of your ocean
Why do ships bend? take a green stick and a dry stick and put flex on both. that's why ships bend.
Nice title card
If you look at pictures of the Titanic, you can see extra strengthening in the middle of the ship, extra plates and beefier rivets holding it together. This was done precisely to give the ship the ability to deal with hogging and sagging, but the builders overdid it. Titanic didn't live long enough to see this become an issue, but her older sister Olympic did, where they eventually realized that the hull had been made too stiff, and small cracks started to form around that extra reinforcement in the middle.
Good stuff. One thing I have wondered about, after watching a few of your videos showing ships in danger of sinking being towed, is what means of a quick disconnect are used to keep the vessel doing the towing from being draged under in such cases?
Is there a reason you aren't on nebula? It definitely feels like a good fit for your channel
Great video, i wonder how much force are they over engineered to withstand compared to like aircraft wings which are designed to withstand 1.5 times maximum expected load
Hearing a man with a posh English accent saying "hogging" is adorable 😆🙂
You forgot to mention metal fatigue building up in the frame and plates. Any metal structure does not have to be that old to start to suffer.
Some torpedoes actually use this to their advantage by exploding underneath the ship. The effect of the shockwave is a bit weaker than with a classical impact torpedo, but the explosion also creates a massive gas cloud, causing the affected part to create less buoyancy. If dome correctly such an attack can rip an entire ship apart
Can you make a video on the MV Arvin breaking in half?
There was a story I have heard about a certain great lakes freighter (I don’t recall which one), where crew said she flexed so much that when going over waves you couldn’t see a door at the end of a hallway
thank Christ I sail the salt seas. inland waters are hidden from God's Love and Mercy
You wouldn't be referring to the 'Edmund Fitzgerald'... ?
@@VerilyVerbatim not the fitzgerald. It was the Carl D. Bradley, just looked it up again to see.
I was expecting to see that clip of somebody filming down a ship's longitudinal catwalk in stormy weather.
Because almost everything is basically a spring.
But also if they weren't bendy they'd be very breaky. Same as wings on an aircraft.
Hi CasNav!
And now I know.
Old photos pointed along the sides of big passenger ocean liners look like they have lots of sagging. Was that real or just an illusion? There's some cargo and fuel to go onboard but it was mostly open passenger space. Did the passenger spaces at the bow and stern of sagging liners have sloped floors, like a carnival funhouse?
you know you got a problem on hand when your entire ship get's Bane'd by the water.
maybe you can do a video about the MOL Comfort Containership
Next video: how much a guy who miscalculated the tension will sit in prison depending on the ship’s cargo
What software do you use for animating
Used to have a professor who would tell us stories about working on some very early FEM modelling of the Liberty ships who famously broke in half due to this effect. They would by hand set up all the parameters for the model, which was then transcribed onto millions of punch cards. Then it was fed onto a "super" computer in England, which crunched it for days before getting a result out(or finding out if there was any mistakes in the math or punches...).
As a contrast, when he told us the stories, a MUCH better model could be done on any old laptop in minutes :P
A hoggy ship sounds adorable.
A tree bends with the wind or breaks. Ships bend with the waves or break. Modern cargo ships have ballast to compensate for the load on top. Is this dangerous? It looks like it, because they are breaking in half.
Then why do ships break up? In 2012, the container ship Rena broke up off New Zealand. In 2021, a freighter breaks up off the coast of Turkey. What do these two cases have in common? Both ships were in a storm. Due to the rides over wave mountains and through wave valleys, the hull is particularly strongly bent. Over time, this leads to Micro cracks/fatigue crackswithin the steel, which spread further and further over time. This can then lead to a breakthrough in another storm. Bending forces may not immediately lead to breakage, but they favour the formation of Micro cracks/fatigue cracks. And these microcracks can become dangerous over time.
I don't think anybody except theoretical physicists assumed that spherical ships don't bend in a vacuum.
Ships aren't spherical, they are elongated box-shaped - We are not talking about cows! 🙂
Or how did Fritz Zwicky put it - "Spherical bastards because, that is bastards no matter which way one looked at them"
I can see the next video title already, "Is water wet?!?"
I'm a carpenter. If my memory serves, a floor is to have no more sag than a 1:180 ratio when loaded. Is there some design standard for large ships?
Two things
1: on a (big) container ship the Chief Officer do not make the stowage plan, it is sent from the office, he just needs to confirm it is safe (I guess the Captain need to do that too)
2: Regarding ships bending from waves at 3:48, isn't that the exact kind of waves you are showing have the same length as the ship?
Something you should avoid sailing directly into, if you have a wave pattern like that you should try to adjust course I thing? anyone correct me.
What I take away from this video is that the motion of the ocean and length go hand in hand.
its the motion of the ocean
water
Double your number of ships with this easy trick cargo companies don't want you to know!
The mocean of the otion :)
Is that the etymology of "hogging" or is that just a mnemonic? In either case, I never made that connection before.
With the wave action I assume fatigue is going to be an issue. Are the ships regularly inspected at critical points?
The where actually several ships that cracked in two, back in the early days of metal ships. Due to fatigue that the engineers had underestimated as they didn't quite understand the effect environmental temperature had on steels properties.
Ie. The engineering margins for fatigue didn't account for the cold water making the steel more fatigue prone.
"Motion of the Ocean"
...sounds sexy
Is this some kind of reupload or some kind of mega dejavu?
Does the weight of container differ, and if so, can this influence the buoyancy of the ship, or do you have to include that in the planning Phase of loading a ship?
Yes, the weight differs depending on the cargo. You have to include that in the planning.
Thank You, so the Person planning knows the weight of every Container?
@@mymax1267 They know the declared weight of every container. Which, as the video alluded to with one sinking, doesn't necessarily mean that they actually know how much each container is, because they may have lied about how much it is (I assume either for shipping rates based on tonnage or illicit cargo)
Would be interested hearing more on this topic: how it plays into the overall longevity of a vessel and how incidents like cargo falling overboard impact the structure of the ship.
So those 1960s Superman comics where Superman rescues a ship by lifting in the middle with one hand and flying with it is all nonsense? My childhood is shattered.
I suppose a flying man is nonsense too?
Does anyone know if icodes used for load planning ships? I know it's used for aircraft and rail but I've always been curious about if it's used for ships.
this says yes ICODES/SSDM - National Defense Transportation Association www.ndtahq.com/wp-content/uploads/2018/10/Slides-Mabee-SDDC.pdf
Hehe...motion of the ocean
Example MOL Comfort
Can you ever have hogging/sagging along the breadth of a ship or is it only along the length? I assume that there would be less due to the smaller distance and there may be stability issues that would arise before it became an issue but is it ever a concern? What about torsion?
The problem that *wasn't* explained.... wave motions travel along the entire length of the hull. It's not a case of the hull bending up and down.... more that it's doing that, with the entire hull length flexing with multiple wave motions across the entire length. Picture that massive cargo ships... VLCC, ULCC, and Ultra-large fuel container ships travelling between continents... the seas can get very rough, especially for ships that have to travel around the southern area of South Africa.
The constant flexing across such very large ships... of course, they bend/flex. They have to, or else the ship would break apart.
@@VerilyVerbatim He was asking if ships would flex in the transverse direction not longitudinal. (like from side to side, port to startboard)
I would say that its only theoretical, not something taken into account.
So no break or topple over
Why not to apply bridge technology: diagonal wires in the middle longitudinal section.
HOG GANG 🤝 SAG GANG
Isn't this a reupload? The content feels familiar
Planning the loading of ships before computers were common must've been quite an annoyance
Yeah, but they were also significantly smaller back then, so there weren’t such a huge number of permutations.
@@awmperry That certainly made it a lot easier, maybe even some problems weren't really that significant back then. But still instead of few people and plugging data to a computer you get a ton of people with a lot of paper calculating on slide rulers.
So that's why the front fell off...
Cuz if no bend, boot break
I guess they don't want their ships to pull a Titanic
to follow the "curve" lol
Is there a chance the ship could bend?
The "Little Captain" sounds like a euphemism for something we really don't want to see from you.
Is this where the phrase "hog eyed" comes from?
I have been on ships and seen the passage way distort. It is a bit unnerving.
Why is the thumbnail so low quality?