Mystery of the Cargo Ships That Sink When Their Cargo Suddenly Liquefies (theconversation.com) 183
An anonymous reader writes (condensed for space): On average, ten "solid bulk cargo" carriers have been lost at sea each year for the last decade. Solid bulk cargoes -- defined as granular materials loaded directly into a ship's hold -- can suddenly turn from a solid state into a liquid state, a process known as liquefaction. And this can be disastrous for any ship carrying them -- and their crew. A lot is known about the physics of the liquefaction of granular materials from geotechnical and earthquake engineering. The vigorous shaking of the earth causes pressure in the ground water to increase to such a level that the soil "liquefies." Yet despite our understanding of this phenomenon, and the guidelines in place to prevent it occurring, it is still causing ships to sink and taking their crew with them.
Solid bulk cargoes are typically "two-phase" materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo. You can read more on this here.
Solid bulk cargoes are typically "two-phase" materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo. You can read more on this here.
This makes it sink? (Score:3, Insightful)
Why does the ship sink, though? Is the material stable in its granular form but without the water binding it is it corrosive or something? TFS wasn't very helpful in explaining why this effect is dangerous or what is being done about it at all. It, however, explained the effect itself fairly well.
Re: This makes it sink? (Score:5, Informative)
From the linked article:
When a solid bulk cargo liquefies, it can shift or slosh inside a shipâ(TM)s hold, making the vessel less stable. A liquefied cargo can shift completely to one side of the hold. If it regains its strength and reverts to a solid state, the cargo will remain in the shifted position, causing the ship to permanently tilt or list in the water. The cargo can then liquefy again and shift further, increasing the angle of list.
Re: This makes it sink? (Score:5, Insightful)
the obvious solution to this is to have partitions inside the ship, to limit the amount of shift possible.
Also, picking "the right ship for the job" such that your cargo comes as close as possible to completely filling the hold to the top, to limit the amount of possible shifting.
I'm just surprised that the pressures added by "drop-filling" the cargo at port have any effect on the possibility of liquifying long after the ship has sailed. I would have expected that only the vibrations during the voyage would have affected it.
I wonder how much of a role uneven loading at port plays? Like if the hold is filled from only a relatively small number of hold covers, leading to cargo that's in roughy pyramid-shaped piles in the hold. If they have just barely enough cohesion to maintain that pyramid shape, I could definitely see how that could shift suddenly and significantly on a rolling sea. Once the shift starts, it's like the article describes, with the entire mass moving as a liquid, a lot like an avalanche, until the pressure drops below critical. And then the cargo "freezes" in place in its new position, quite likely creating a dangerous imbalance in the load.
I've always found watching avalanche videos to be fascinating, how snow, seemingly solid, can flow like a river, and then suddenly stop as if hit by a freeze ray, cementing everything in place. Trees, cars, people, buildings, everything is moved like it's being carried away by a tsunami, and then suddenly it all just stops. Landslides are the same eerie way. It's like god is playing "red-light-green-light" with giant hunks of material.
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This. Baffles for liquid transport (even fuel tanks in vehicles designed for non-cargo purposes) along with sectioning tanks is not even remotely new. So
a) treat bulk solid powders like bulk liquid
b) dehumidify the hold
c) have a spray down for offload if getting every last grain is desired (adding baffles and bulkheads increases surface area, which will increase losses due to product sticking to surfaces)
Re: This makes it sink? (Score:4, Insightful)
the obvious solution to this is to have partitions inside the ship, to limit the amount of shift possible.
Also, picking "the right ship for the job" such that your cargo comes as close as possible to completely filling the hold to the top, to limit the amount of possible shifting.
Baffles will increase mass, weight and make loading and unloading of cargo much slower.
As for the second point, what will all the specialised ships do whilst not being employed for a single task? Freighters cost millions to make, every day they sit empty or idle is a day they're costing money.
The best and simplest solution is to find out why cargoes are liquefying, its not something that happens that often. 10 ships a year. There are an estimated 11,000 bulk carriers in service.
Re: This makes it sink? (Score:5, Informative)
Not arriving at port also makes unloading much slower...
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Actually, there's no reason for the baffles to extend all the way to the bottom of the hold. The bottom could still be open to allow material at the bottom to shift around. If your unloading mechanism is built into the bottom of the ship (as they are on newer bulk carriers), then the baffles will barely affect unloading operations. Fuel tanks are built this way [supermotors.net]
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10 out of how many? We are talking about ships sailing everyday all over the world.
There are more car accidents per second than that.
Yes it will cost more (Score:4)
Baffles will increase mass, weight and make loading and unloading of cargo much slower.
And that is somehow worse than the loss of the ship and possibly the crew?
As for the second point, what will all the specialised ships do whilst not being employed for a single task?
Sit idle. Yes this will make the cargo cost more to carry. That's just how the cookie crumbles sometimes. Ships for liquefied natural gas don't get converted to haul coal when not carrying cargo. If safety demands a specialized ship then so be it.
The best and simplest solution is to find out why cargoes are liquefying, its not something that happens that often.
And then what? They evidently already know why they are liquefying. The question is what to actually do about it which will almost certainly involved some amount of change to ship design and cargo procedures.
Re: Yes it will cost more (Score:2, Interesting)
The ship is insured and the crew expendable.
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The ship is insured
If the shipping company redesigns their ships, they can reduce the likelihood of a ship being lost.
If they reduce the likelihood of a ship being lost, they reduce how much insurance pays out to them.
If they reduce how much insurance pays out to them, they can successfully argue for lower rates.
So I can only conclude that either, 1) it would cost more to redesign the ships than would be saved, or 2) the insurance companies don't know that the shipping companies are choosing to not do more to mitigate shi
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Except it isn't really 10 ships out of 12,000. It is ten per year out of 12,000. This means the half-life of a ship is only 600 years. That seems way too short to me.
But the more alarming statistic is that only about two dozen large ships go down in a typical year. Thus, this one cause alone is responsible for about 42% of the major ship losses, which is to say nearly as much as all other causes combined. That's staggering, as it
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I think most people would consider a 600 year old ship a national treasure :)
I like your insight though, it's more useful context than the raw '1 in 12000' number.
Re:Yes it will cost more (Score:4, Insightful)
And that is somehow worse than the loss of the ship and possibly the crew?
In-humanness of the response aside, the risk is quite low, ships are replaceable, and crews are typically from poor countries where life is cheap. These aren't your western well paid sailors who are mourned and whose companies get sued into oblivion for providing unsafe work locations.
Unfortunately the answer to your question is yes.
Sit idle. Yes this will make the cargo cost more to carry.
Only if the costs are spread across the industry. If the costs are only carried by the one company prioritizing safety over cost then cargo won't cost more to carry, it will simply put one competitor with a conscience out of business.
If safety demands a specialized ship then so be it.
Are you talking about the customer who doesn't want to pay or the hauler who doesn't want to bear an additional cost when their competitors don't?
The question is what to actually do about it which will almost certainly involved some amount of change to ship design and cargo procedures.
Indeed. But the answer is not to jump to expensive and impractical solutions that won't see implementation without a concerted effort across the entire industry. Shit man for hazardous cargo the industry in the past 30 years hasn't even agreed to a standardised way to emergency shutdown their unloading pump. Good luck getting them to implement something that actually cost them money.
Re:Yes it will cost more (Score:5, Interesting)
This is a common trope, but it's simply not true. The number of cargo ships lost at sea [theguardian.com] about equals the number of lives lost aboard those ships [ics-shipping.org]. That is, on average about 1 person dies for each ship that sinks.
The vast majority of people aboard a cargo ship which sinks are rescued. Life rafts are required by all shipping regulators. And satellite locator beacons have become so cheap that I suggest you get one [rei.com] if you do things like boating or hiking.. Their cost (a few hundred dollars, though a commercial model will run a few thousand) is much less than the liability and bad publicity of someone dying because your ship sank. When someone dies, it's usually because they were unable to reach the life raft in time (injured or blocked in due to the accident which sank the ship).
In fact, the fatality rate works out to (100 deaths) * (100,000) / (1.25 million) = 8 per 100,000. That makes it safer than a variety of jobs [washingtonpost.com] as mundane as taxi driver or landscaper. The fatality rate is right around the average for all jobs if you account for those people being aboard the ship 24/7, while people are at the other occupationss on average for less than 6 hours a day.
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This is a common trope, but it's simply not true.
So you conclude that it's not true and back your data by showing that the industry none the less kills many people each year? I'm not sure what you're trying to prove here. The fatality rate of shipping seems to be quite in line with fatality rates in other industries and just like other industries the fatality rate is higher in cargo hauling than it is in localised western sea faring industries like fishing.
Just because the numbers are low or trending down doesn't make it any less true.
And yes I own an EPI
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hmmmm....
So, if we reduce the cargo capacity (and at the same time, increase time required to unload the ship) by, say, 5%, we have a ship that makes ~90% as much as "normal". And costs, say, 5% more.
So we have to charge ~15% more per ton moved to pay for the ship. Which makes us the last choice of anyone trying to move cargo, since they're hav
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It really is. Do you have any idea how many ships are out in sea this very second?
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As for the second point, what will all the specialised ships do whilst not being employed for a single task? Freighters cost millions to make, every day they sit empty or idle is a day they're costing money.
That point is moot as bulk cargo ships ARE the specialised ships compared to the generic container frighters.
But if the problem is actually the water between solid particles.... wouldn't a drain and a bilge pump in the hold not get rid of the excess water?
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No.
Even at a macro level, you water pot plants by putting water in the base of the pot and letting it rise up through the soil to reach the roots. You aren't going to completely dry the soil again by draining the base.
At a more detailed level, very few materials are truly dry. Solid rock contains water and (m)any granular material can be subject to fluid dynamics. I suspect liquefaction uses the trace lubrication inherent to the materials being transported, rather than a simple excess of water.
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I understand and agree with that, but my flowerpot doesn't suffer from sudden liquidification.... I understood that happens when the water that is usually safely contained within the material escapes and acts as lubrication, like the air in this video:
https://www.youtube.com/watch?... [youtube.com]
but as the water is then no longer contained, it could be drained and removed (as the added air bubbles off on top of the sand in the video)
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Have you tried gently rocking your flower pot from side to side for four weeks without a break? :)
Someone lower down posted a more informed response detailing how it works, so I'll let you read their reply rather than repeating it badly here.
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10 ships a year. There are an estimated 11,000 bulk carriers in service.
And assuming 10 voyages a year this is one loss per 10,000 loads delivered. Using the Wikipedia bulk carrier article (which is quite good) and taking a large carrier of 80,000 tons that costs $40 million new, it would deliver 800 million tons per ship lost, or about 5 cents per ton as the "lost ship toll". Actual shipping fees listed are on the order of $15-70 per ton, so this is hardly even round-off error to the huge corporations that own these ships.
The crew of 20 to 30 people, almost entirely recruited
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Baffles will increase mass, weight and make loading and unloading of cargo much slower.
This is why we have regulations. It levels the playing field so EVERYONE has this expense. And it also solves the "Someone elses problem" of ships sinking. The ship is insured, so the shipping company doesn't have any vested interest in safety. The people who run the company are safe on dry land, so they're just apt to say "shit happens". There's likely smaller companies where the captain/crew might also be the owner
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Too many regulations that reduce profit and the ships (and owners) will flag from a different country.
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LOL - And who sets and enforces these regulations?
Or did you think we were just talking about one country's ships?
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I risk dead farmers, dead lorry drivers, dead bakers every time I buy a loaf of bread.
You really think I'm going to give a shit about risking dead sailors?
Head to a poverty stricken port. "Guys, starve to death or work on this ship which is likely to sink at some point in the next 600 years, leaving you drifting in a modern well equipped lifeboat"
I'm not going to pretend it's ideal, but it compares well to, "Guys, I have no jobs today. I couldn't operate a raw materials transport business at sufficient prof
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the obvious solution to this is to have partitions inside the ship, to limit the amount of shift possible.
...
Except that might make loading and unloading cargoes such as bulk ores difficult or impossible, depending on the vessel and the port facilities.
The large machine in TFS sure looks a lot like a Hulett unloader [wikipedia.org], and those only work with wide-open, flat-bottomed holds.
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the obvious solution to this is to have partitions inside the ship, to limit the amount of shift possible.
Take a look at the commentary on Ars. Partitions in the hold are the first thing every nerd proposed, but apparently maritime cargo operates by the same bean-counting rules as the automobile industry: any innovation that costs more than pennies per unit is rejected as too costly. Losing a rusty freighter with a developing-nation crew every so often is just a cost of doing business.
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We need a regulation outlawing dying!
Then we can live forever or face fines :)
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the obvious solution to this is to have partitions inside the ship, to limit the amount of shift possible.
As others have pointed out, this idea becomes impractical for various reasons.
A perhaps better solution is to control liquification to a greater degree. One idea that comes to mind is to lower the ratio of solid to water during loading, so as to ease the loading process and better even-out the cargo, and then raise the ratio by pumping out some of the water, locking the load into place. During unloading, the reverse happens.
The extra time required can be mitigated by performing some of the pumping out in
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Can't. You might not know this, but ships sail in water, and water around the wrold is quite different. How full you can load a ship depends on the waters it's going to sail in - different salt content, etc. really affect the loading of the ship.
While loading is calculated by computer nowadays, Plimsoll Lines help anyone looking at the
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The problem comes from the desire to more rapidly load and unload a ship to increase profits. Having partitions or baffles will slow this process down. Like anything to do with profits, the risks are evaluated and considered acceptable by those in charge.
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They're not in containers. They solids are directly into the hold, so it acts like a giant dump truck filled with sand.
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Just put them in sealed containers? If it's a known problem that affects a dozen ships a year (very expensive ships with lots of cargo) then wouldn't containers for the cargo be pretty straightforward? I know it adds weight but wouldn't that be preferable to losing ships every year? (And my confusion was more with the summary as it should have had the basic info... thanks slashdot)
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Probably not preferable, no. Adding weight and complexity and therefore costs to all haul of 11.000 ships vs. losing 10 ships a year - I'd expect it's cheaper to just lose the ships.
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I'm sure someone in the industry has run the numbers before you and determined the risk/reward was worth the loss.
Yes, believe it or not, people's lives money. Stupid isn't it?
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What's even more stupid is my "less than" symbol was completely removed from my post. Great job Slashdot.
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Almost all freight is containerized. If bulk cargo were reasonable to containerize, it would have happened long ago, to avoid specialized ships entirely.
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Re:This makes it sink? (Score:5, Informative)
Re:This makes it sink? (Score:4, Insightful)
I guess fitting baffles or compartments to bulk carriers costs more than the insurance when a ship goes down.
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I guess fitting baffles or compartments to bulk carriers costs more than the insurance when a ship goes down.
Retrofitting would be expensive, but I could see building new ships with a different hold layout. Instead of multiple holds aligned one in front of the other forward to aft, have them run forward to aft and be aligned side to side port to starboard. This way if the load shifts you still have weight to counterbalance.
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True, due to the shape I could imagine it being more resilient to weight shifting front to back rather than side to side.
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The liquefied solid probably sloshes around, and when you displace this amount of weight in a cargo ship, it can lead to some pretty nasty things structurally.
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Why does the ship sink, though? Is the material stable in its granular form but without the water binding it is it corrosive or something? TFS wasn't very helpful in explaining why this effect is dangerous or what is being done about it at all. It, however, explained the effect itself fairly well.
Likely it's the "free surface effect" [wikipedia.org]. Basically, if tanks or holds aren't full, when the ship rolls to one side, the cargo flows to that side too, moving the ship's center of gravity towards the low side. Get enough of a flow and the vessel can capsize, or the momentum of the flow can damage the ship:
The free surface effect is a mechanism which can cause a watercraft to become unstable and capsize.
It refers to the tendency of liquids — and of unbound aggregates of small solid objects, like seeds, gravel, or crushed ore, whose behavior approximates that of liquids — to move in response to changes in the attitude of a craft's cargo holds, decks, or liquid tanks in reaction to operator-induced motions (or sea states caused by waves and wind acting upon the craft). When referring to the free surface effect, the condition of a tank that is not full is described as a "slack tank", while a full tank is "pressed up".
Stability and equilibrium
In a normally loaded vessel any rolling from perpendicular is countered by a righting moment generated from the increased volume of water displaced by the hull on the lowered side. This assumes the center of gravity of the vessel is relatively constant. If a moving mass inside the vessel moves in the direction of the roll, this counters the righting effect by moving the center of gravity towards the lowered side. The free surface effect can become a problem in a craft with large partially full bulk cargo compartments, fuel tanks, or water tanks (especially if they span the full breadth of the ship), or from accidental flooding, such as has occurred in several accidents involving roll-on/roll-off ferries.
If a compartment or tank is either empty or full, there is no change in the craft's center of mass as it rolls from side to side (in strong winds, heavy seas, or on sharp motions or turns). However, if the compartment is only partially full, the liquid in the compartment will respond to the vessel's heave, pitch, roll, surge, sway or yaw. For example, as a vessel rolls to port, liquid will displace to the port side of a compartment, and this will move the vessel's center of mass to port. This has the effect of slowing the vessel's return to vertical.
The momentum of large volumes of moving liquids cause significant dynamic forces, which act against the righting effect. When the vessel returns to vertical the roll continues and the effect is repeated on the opposite side. In heavy sea states, this can become a positive feedback loop, causing each roll to become more and more extreme, eventually overcoming the righting effect leading to a capsize. While repeated oscillations of increasing magnitude are commonly associated with the free surface effect, they are not a necessary condition. For example, in the cases of both the SS Normandie and MS al-Salam Boccaccio 98, gradual buildup of water from fire-fighting caused capsizing in a single continuous roll.
Google "free surface effect" images [google.com]
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Yup... seriously. That would have been the most obvious thing to put in the summary, and they didn't!
I guess it's effectively like a load-shift in an aircraft.
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Why does the ship sink, though? Is the material stable in its granular form ...
Other people did a good job explaining this, but you can also see this effect in the movie, and chapter 15 of the book, The Martian, during the launch failure of the Iris re-supply probe. (The scene also explained here [quora.com]).
From The Martian, Chapter 15:
At the microscopic level, the protein cubes were solid food particles suspended in thick vegetable oil. The food particles compressed to less than half their original size, but the oil was barely affected at all. This changed the volume ratio of solid to liquid dramatically which in turn made the aggregate act as a liquid. Known as "liquefaction," this process transformed the protein cubes from a steady solid into a flowing liquid.
Stored in a compartment that originally had no leftover space, the now-compresses sludge had room to slosh.
The shimmy also caused an imbalanced load, forcing the sludge toward the edge of the compartment. This shift in weight only aggravated the larger problem and the shimmy grew stronger.
This was part of a cascade failure [wikipedia.org]. The vibrations from the rocket caused the protein cubes to liquefy, which sloshed around, creating an unbalanced load, causing a procession, causing a launch failure.
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There are examples of liquefaction that take place during earthquakes, where what had been solid ground seems to just dissolve.
I believe the theory is that vibrations of the correct frequency and amplitude can cause the cargo in a cargo ship to liquefy in a similar fashion, but the specifics are going to depend a lot on what the cargo is and what the water content is. The article was pretty light on specifics, however.
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If you're right, that merely elevates the article from "crackpot claptrap" to "shoddily written clickbait". The mystery is less what happens than why it happens only to some ships, and why ship owners don't take the safety measures that are described in other comments here.
Re:This makes it sink? (Score:5, Informative)
If you're right, that merely elevates the article from "crackpot claptrap" to "shoddily written clickbait". The mystery is less what happens than why it happens only to some ships, and why ship owners don't take the safety measures that are described in other comments here.
The article and accompanying discussion addresses these questions and was technically interesting and high quality. "A lot is known about the physics of the liquefaction [...] Yet despite our understanding of this phenomenon (and the guidelines in place to prevent it occurring), it is still causing ships to sink and take their crew with them."
The technical answer is that the existing guidance on stowing and shipping solid bulk cargoes is too simplistic. Liquefaction potential depends not just on how much moisture is in a bulk cargo but also other material characteristics, such as the particle size distribution, the ratio of the volume of solid particles to water and the relative density of the cargo, as well as the method of loading and the motions of the vessel during the voyage.
The economics make it clear that it's not worth spending huge amounts of money (that also make ships more awkward to load) for an event that's comparatively rare. It's doubly not worth spending money on refits when we don't even have a good physics model of it, one that's backed by data+observations. And if we kitted out some experimental ships but they proved to be in the 99.9% of ships that aren't affected by the phenomenon, then we won't have gathered any data.
The main idea in this thread was lengthwise bulkheads. I've never seen a ship designed that way. Not sure why. Maybe because it's a bulkhead that would need to be seriously strong (to stop the millions of tonnes) and would contribute nothing to the structure of the ship; only weight. Another idea was pumps to remove the water. Those would have to be exceptionally robust to handle being hammered by lumps of bauxite, and not get clogged by the finer bauxite. Maybe you could put a pump behind a mesh, if you could invent a mesh that would stand up to the millions of tons. The article suggests that another cause might actually just be the *speed* of loading. If that's true, how would we measure+test that? Could we invent a different loading technique that's mostly as fast? It'd be massively cheaper than lengthwise bulkheads.
There's a good video too: https://www.youtube.com/watch?... [youtube.com]
In the video, the Australian Maritime Safety Organizations suggests a different preventative measure which is - captains should be aware that this is a phenomenon, aware of what are the warning signs, should pay attention to those first signs, and should consider seeking a Port of Refuge.
In short - excellent article, interesting phenomenon that even though we know about liquefaction and know about ocean shipping most of us still wouldn't have thought of, is deeper than "just add bulkheads".
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why it happens only to some ships
Citation?
It probably happens to 100% of bulk haulers, but the shifted load is not enough to sink the ship.
why ship owners don't take the safety measures that are described in other comments here
The ship is insured and the crew are expendable.
Roughly 1% of bulk haulers sink from this, so your fix is going to have to be cheaper than the insurance premium for a 1% chance of sinking for the owners to care.
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Or... the crew is much more likely to die on their way to work than from this situation sinking their ship and destroying their means to escape that sinking ship.
Re: This makes it sink? (Score:2)
They rolled over it to simply the explanation. But that specific type of friction effectively goes to zero. Similar to a standing vs rolling ball. The former has effectively zero rolling friction and the latter has effectively zero static friction. And of course neither has sliding friction.
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I took this as "friction between the solid particles". Maybe the particles shrink more from compression due to pressure than the surrounding liquid, at some point they are no longer in direct contact, and before that the force with which the particles are pressed against each other at contact points goes to zero, which also makes the friction between particles go to zero.
Or maybe it's just engineers talk meaning "the friction is reduced by some orders of magnitude".
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Solid materials have "friction"; liquids have "viscosity". So, technically there's no friction once it liquefies. It could have been put better, clearly.
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Because really, when considering how water moves in a container such as a ship, calculating the friction *within* the actual water itself *technically* would make the simulation more accurate, but on such a unbelievably small
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There's an urban legend that glass is a liquid that just flows slowly, purporting to explain why old glass panes are wavy, and thicker at the bottom than the top. But that's all BS - old glass was wavy when installed, and of course you put the thicker side down so it doesn't fall over while you put the frame around it. Smooth glass of even thickness, "float glass", is a surprisingly recent invention, only commercially viable in the late 1950s.
Preventable (Score:5, Insightful)
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Which also points to the most likely cause, poor maintenance of the drive line and hull harmonics. That would be the whole drive line, engine, engine mounts, transmission, transmission mounts, drive shaft, bearings, and the propeller. Environmental conditions would be to slow to promote liquefaction, not of the entire cargo but more likely only the bottom half, with the top half floating on top and shifting. Drive shaft load and balancing versus changes in hull shape under load, would be a likely source of
Re: Preventable (Score:2)
I remember reading about the marking on a ship's hull that indicate the maximum load you should carry in different seas. The reserve floatability should be larger the rougher the seas. Thus NA meaning North Atlantic is the roughest, FT meaning Fresh Tropical is easiest (you can load the ship to maximum).
Now what was really interesting was how long it took for the British parliament to pass the law. Decades. And the merchants tried everything to stop it up to attempts to discredit the politician that propose
Could injecting gas from the bottom help? (Score:5, Interesting)
As far as i understand they have a mixture of solid particles surrounded by liquid, the particles are more compressible, so under pressure the whole structure loses coherence as effectively the solid fraction is reduced, since the liquid is less compressible.
I wonder if this could be helped by injecting some gas from the bottom after loading, so there are pockets where the granular solid is surrounded by compressible gas instead of liquid. If the density of the liquid is less than that of the solid surplus liquid would be driven to the top where it could be extracted.
It might help if the gas pockets are well enough dispersed.
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I’m thinking that might be a bad idea [youtube.com]. Or at least something that would need to be done carefully.
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As far as i understand they have a mixture of solid particles surrounded by liquid, the particles are more compressible, so under pressure the whole structure loses coherence as effectively the solid fraction is reduced, since the liquid is less compressible.
I wonder if this could be helped by injecting some gas from the bottom after loading,
The short answer is no. If you inject gas into a mixture of solid particles, you reduce the friction between them as the gas passes through them. You'd actually be making the problem worse. Some people have experimented with sand tubs using precisely this effect. You inject a bunch of air into the bottom and it makes the sand act a lot like a liquid. You can sink into it, and move your limbs through it.
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The reason bulk carriers work is because they're simple. The weight that goes into these ships is almost unbelievable, and adding moving components to the very bottom of that weight is a recipe for disaster. Bulk carriers are used for homogeneous goods sold in mass quantities for prices low enough that putting them in containers is cost prohibitive. I'm surprised that this is an issue, but I could see why the hold would have limited possible fixes for a situation like this. I think the eventual fix woul
Cargo? (Score:2)
What sort of cargo are they carrying that is a granular solid filled with water?
Re:Cargo? (Score:4, Informative)
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Grain too contains water. Drying is necessary to prevent spoilage but it cannot drive out all water and then there is humidity to consider.
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Re:Cargo? (Score:5, Informative)
In this case, bauxite.
The PDF linked from the article has a FAR better explaination:
http://www.imo.org/en/MediaCen... [imo.org]
Re:Cargo? (Score:4, Interesting)
One of the major bulk cargos cited was bauxite, aluminum ore. Though most ores are smelted near the mine, the economics of aluminum are weird because this element requires vast amounts of electricity to refine. It actually pays to mine bauxite in Australia but smelt it in places like New Zealand, where there is cheap hydro, or Iceland, where there is cheap geothermal electricity.
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Liquefaction (Score:5, Interesting)
Clickbait headline (Score:3)
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Compartmentalization (Score:4, Interesting)
Out of curiosity, do these bulk cargo vessels store their loads in one big hold, or are the holds compartmentalized? If the ships have multiple holds (say 3), each side by side and running lengthwise, then even if the loads in each hold liquefy and shift to port, the loads in the center and starboard holds may still have enough weight to counteract the shift.
A quick google search turns up this image [netdna-ssl.com], showing a stern to bow layout. So if the load in one hold shifts it is likely that all the others will shift too. So running the holds bow to stern and stacking them port to starboard would solve that issue. Given the size of these vessels I would assume that loads shifting forward or aft would be less of an issue or concern, but you could always make 6 holds by running 3 along the length of the ship and separating them midship.
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So running the holds bow to stern and stacking them port to starboard would solve that issue.
Changing loading / unloading practices internationally due to a handful of ships being lost a year is not something that will gain much traction, especially not when the changes affect the one party who is otherwise completely by the loss of a ship and cargo.
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So running the holds bow to stern and stacking them port to starboard would solve that issue.
Changing loading / unloading practices internationally due to a handful of ships being lost a year is not something that will gain much traction, especially not when the changes affect the one party who is otherwise completely by the loss of a ship and cargo.
What's to change? They load from the top through hatches using cranes on the vessel. So, instead of 3 long holds make them 2, one port and one starboard with a bulkhead amidship making 4 total holds(port/forward, port/aft, starboard/forward, starboard/aft). Run the cranes amidship as well so they can service both holds. Problem solved.
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What's to change? They load from the top through hatches using cranes on the vessel.
Practices. I didn't say the change is big or complicated, just that it won't be done. For the past 30 years the industry has been talking about an emergency stop signal for unloading pumps on hazardous material vessels. The cost would be a relay, a connector and a cable on each boat. 2018 and they are still *talking* about it.
To say the entire industry is resistant to change would be the understatement of a lifetime. The only reason what you say can't be done is because it isn't done. Nothing more than that
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Some use cranes on the ships. Some use cranes on the port. Some use conveyor belts, which can be the cheapest and fastest. Ships that "unload themselves" use conveyor belts.
Think about parallelizing movement of bulk freight between ship and port. A bunch of cranes or belts spaced out along the length of the ship, with roughly square hold compartments, is straightforward. A bunch of long, thin compartments running lengthwise not so much. Conveyor loading into long, thin compartments doesn't really work
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There is a good Wikipedia article on bulk cargo ships [wikipedia.org]. It contains such useful information as this (edited excerpts from two paragraphs):
Bulk carriers are designed to be easy to build and to store cargo efficiently... Double hulls have become popular in the past ten years... One of the advantages of the double hull is to make room to place all the structural elements in the sides, removing them from the holds. This increases the volume of the holds, and simplifies their structure which helps in loading, unloading, and cleaning.
So these vessels are all about doing stuff as cheaply as possible to minimize the cost of operation, and a key strategy is to keep all obstructions out of the hold. With compartments they would then have to be loading and unloading and cleaning each compartment separately, taking more time and effort. Putting in compartments defeats the design goal of the bulk carrier. Als
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Except that they have to load and unload the cargo through hatches. Think, for a moment, how you would arrange the hatches so that all of the cargo could be reached through them if the holds are running lengthwise, and for that matter, how the loaders and unloaders would need to change from the current setup.
They already load/unload these ships from the deck and down into the hold. What would change? At worst you just need more/bigger hatches.
I'm not saying it was Aliens (Score:2)
Summary (Score:4, Funny)
This is a remarkably good summary for Slashdot.
no water in earthquake liquefaction (Score:2, Interesting)
A lot is known about the physics of the liquefaction of granular materials from geotechnical and earthquake engineering. The vigorous shaking of the earth causes pressure in the ground water to increase to such a level that the soil "liquefies."
Nope!
Ground water in the soil has nothing to do with earthquake liquefaction. Liquefaction can occur without any water present at all.
See, e.g., https://www.britannica.com/science/soil-liquefaction
TL:dnr: [vibration] causes otherwise solid soil to behave temporarily as a viscous liquid.
As for cargo ships filled with bulk wheat, rice, etc.; it's kinda stating the obvious that, while they are solids, in the sense that they are not liquids, they also aren't solid like a blocks of wood, rolls of steel, or pigs
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Or aim a laser at a ship full of popcorn kernels.
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https://www.britannica.com/sci... [slashdot.org]>Your own link says otherwise. "The phenomenon occurs in water-saturated unconsolidated soils affected by seismic S waves (secondary waves), which cause ground vibrations during earthquakes."
And then reading further:
"When earthquake shock occurs in waterlogged soils, the water-filled pore spaces collapse, which decreases the overall volume of t
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Liquefaction absolutely requires a fluid between the particles - that can be air, water or a mixture of both. All that is required is that the effective stress [wikipedia.org] be reduced to zero. Most granular materials, regardless of particle size distribution (grading), will exhibit zero shear resistance when the effective stress is zero, and so any loading will cause them to move. Liquefaction in particular is caused by vibration, where the shaking builds up pore water pressure which cannot dissipate fast enough beca
well, sure (Score:2)
Solid bulk cargoes are typically "two-phase" materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo.
Um, yeah, I was gonna say that. Sure. Everyone knows that, right?
;)
Liquid Evil (Score:2)
So THIS is why the TSA only allows a few ounces of liquids on carry-on. Down with those fucking liquids! I'm doing my part by boycotting all liquids, for approximately the next three days.
Liquefaction (Score:2)
Note that it doesn't really turn into a liquid - it turns into individual particles that as a group and flow and appear to act much like a liquid. TFS (and TFA) slightly confuse the issue by suggesting or implying that the water turns it into something like mud. The same thing is possible in materials that are effectively free of water, it's just vanishingly unlikely.
The same effect can happen during earthquakes on "landfill" like most of the land around the edges of the SF Bay area.
It's not a mystery (Score:2)
...if they know why and how it happens.
Danger to the crew? (Score:2)
it is still causing ships to sink and taking their crew with them.
Are crews actually being lost? Seems like it wouldn't sink so fast that they wouldn't be able to abandon ship to lifeboats first. That seems a bit dramatic unless the ships capsize so suickly there is no hope for reaching the boats.