Baltimore Bridge Collision and Collapse

[rcktnut]

Another bridge hit today: https://www.msn.com/en-us/news/us/b...ng-an-oil-spill/ar-BB1mrItE?ocid=BingNewsSerp

 

[NTP2]

Another bridge hit today: https://www.msn.com/en-us/news/us/b...ng-an-oil-spill/ar-BB1mrItE?ocid=BingNewsSerp

Quite a bit milder through.

 

[MClark]

Every bridge that gets bumped will be breaking news.

"….said the rail line only serves as protection for the structure and has never been used.….
I guess it worked.

 

[MarsLander]

I'm a CFI and commercial pilot. I follow Blancolirio channel on YT. He mainly does aviaition accidents. However, the parallels are there for the comparison, aviation to shipping systems. Liked his breakdown.

 

[Capt. Eric]

I'm a CFI and commercial pilot. I follow Blancolirio channel on YT. He mainly does aviaition accidents. However, the parallels are there for the comparison, aviation to shipping systems. Liked his breakdown.

I'm sorry, but I couldn't watch it after the first 2 minutes. All he was doing was reading the NTSB report, pretty much word for word. I know how to read, and already read it. He may know airplanes, but no, a ship is not at all like an airplane. The only thing similar in the electrical systems are they both involve the flow of electrons. The main engine of a ship is a slow speed diesel, which if I recall from my engineering class, is a little different from a turbo fan or jet engine. Maybe he did say something insightful later on, but I'm not optimistic.

 

[rharshberger]

I'm sorry, but I couldn't watch it after the first 2 minutes. All he was doing was reading the NTSB report, pretty much word for word. I know how to read, and already read it. He may know airplanes, but no, a ship is not at all like an airplane. The only thing similar in the electrical systems are they both involve the flow of electrons. The main engine of a ship is a slow speed diesel, which if I recall from my engineering class, is a little different from a turbo fan or jet engine. Maybe he did say something insightful later on, but I'm not optimistic.

IMO one important thing was that they reset the two breakers that had just tripped rather than switching over to the other set, usually if a breaker trips there is a reason, and its likely to do it again...almost immediately, so I think that was a fail on the crews part. But I don't know ships...or aircraft for that matter, I do know a little bit about breakers though.

 

[cbrarick]

I wonder what was in their operator's manual. that may explain why they shut it again, or the ship i served on, sometimes the operating procedures would call for you to reset the breaker. I think the theory was that perhaps a downstream breaker would open allowing a vital bus to have power to everything else. It's been a long time, however. My memory might be faulty

 

[Capt. Eric]

IMO one important thing was that they reset the two breakers that had just tripped rather than switching over to the other set, usually if a breaker trips there is a reason, and its likely to do it again...almost immediately, so I think that was a fail on the crews part. But I don't know ships...or aircraft for that matter, I do know a little bit about breakers though.

Those details of crew actions may be laid out in the final report, which will be months or a year from now. My guess is that they may have opened some non-critical equipment breakers (fans, ac, reefers, etc.) on the way to closing those again. Typically, the engineers might then check a few obvious causes and troubleshoot before putting those other things back online one by one.

 

[boatgeek]

Here's a comment from a former co-worker, who was one of the best marine electrical engineers in the country before he retired:

Up front I don’t understand why the crew “manually” reset everything. This vessel surely had a control room with full remote control of the electrical system. But, moving on from there:

I don’t understand the operating configuration when leaving port, even if they had had some spurious loss of electrical in port (why didn’t that raise some eyebrows?). If DG3 and DG4 were online, I would have had HR2 and LR2 closed so that if the HVR bus tie opened, you would still have LV. In the configuration they had when leaving harbor, if any of HVR, HR1 or LV1 open, you lose all LV. And personally, when in a sensitive operation like leaving harbor, I would have had a DG on each side running, HVR closed, and both TR1 and TR2 energized with LVR open. That way, any single breaker opening would have almost no effect. Even three breakers opening would not have shut down the Main Engine.

I guess in the end, it comes down to why did the breakers open? Had someone been doing maintenance in the swbds? I need to hear that finding. But as I said, the configuration they were in was about as bad as it could be.

These guys were looking for a disaster. They did almost everything electrical wrong.

For reference, here's the simplified one-line with the breakers and gensets labeled.

 

[Bravo52]

Well, we were all treated with different opinions and lore about how this bridge collapsed and even a "theory" or two about why, now we are starting to hear the battle about who and how it will be paid for. Apparently, the first meeting of the accountants and politicians occurred and there seems to be some differing thoughts on who will pay.

One burracrate said; "Oh, we can give you 90% but who's coming up with the rest?" The rest is about $200M. Of course some want that plumber down in Arizona to pay for the bridge along with a few of his buddies around the country, but not only do the Maryland and one Delaware (I think Delaware but the story always changes) want taxpayers to pay, they want to then charge those same taxpayers a toll to use the bridge they paid for...

The lawyers are lining up to get their share too. Seems there are a few players in the mix. The ship owner, the ship manager, the USCG, and most importantly, the Baltimore harbor pilots who were responsible for the ship. This fight will be the "mostest" fun!

 

[Bravo52]

@boatgeek and @Capt. Eric ... quick question on the electrical system. After Boatgeek's comment on the NTSB report, it seems like this whole problem started with some CBs popping on non-essential equipment....but, that were tied to critical equipment. It begs the question as to why aren't critical systems isolated from non-critical systems? Why is the ship's steering tied to some crew member's mini-fridge?

 

[Peartree]

Well, we were all treated with different opinions and lore about how this bridge collapsed and even a "theory" or two about why, now we are starting to hear the battle about who and how it will be paid for. Apparently, the first meeting of the accountants and politicians occurred and there seems to be some differing thoughts on who will pay.

One burracrate said; "Oh, we can give you 90% but who's coming up with the rest?" The rest is about $200M. Of course some want that plumber down in Arizona to pay for the bridge along with a few of his buddies around the country, but not only do the Maryland and one Delaware (I think Delaware but the story always changes) want taxpayers to pay, they want to then charge those same taxpayers a toll to use the bridge they paid for...

The lawyers are lining up to get their share too. Seems there are a few players in the mix. The ship owner, the ship manager, the USCG, and most importantly, the Baltimore harbor pilots who were responsible for the ship. This fight will be the "mostest" fun!

I would think that some of the crew members (especially officers) would want their own lawyers at some of these meetings as well. I wouldn't trust that my employer's lawyers wouldn't throw me under the bus at their earliest convenience.

 

[Capt. Eric]

@boatgeek and @Capt. Eric ... quick question on the electrical system. After Boatgeek's comment on the NTSB report, it seems like this whole problem started with some CBs popping on non-essential equipment....but, that were tied to critical equipment. It begs the question as to why aren't critical systems isolated from non-critical systems? Why is the ship's steering tied to some crew member's mini-fridge?

Basically, the ships generators power everything. You can't have separate generators and switch boards for this, and for that. Not very efficient or redundant. Typically, and true here according to the report, there are 2 generators online during port transits, but 1 would usually be enough. So you have plenty of capacity. Then another is on standby and will start automatically if the others start losing power or if demand increases. That all seems to have been in place here. The big unanswered question is why did these breakers trip. We don't know that yet. Once those tripped, the rest cascades into loss of control of the vessel. If they had a little more time and distance, they could have recovered from this. A bad place for this to happen.

And to answer Boatgeek's friend's question, no, most electrical systems on ships are not fully automated or remote control. Some aspects might be, but it is not like a computer controls everything, and you don't sit in front of A computer screen to control the breakers that are in the panel 3ft behind you. I can't speak to the other points he raised as I'm not quite that well versed in that.

Finally, Bravo52 - note that pilots are advisors and are not responsible for a ship (with one exception, but that's a different subject). They will not have any culpability here, and in fact acted very well, and saved lives.

 

[Capt. Eric]

I would think that some of the crew members (especially officers) would want their own lawyers at some of these meetings as well. I wouldn't trust that my employer's lawyers wouldn't throw me under the bus at their earliest convenience.

Those guys can't afford lawyers.

 

[boatgeek]

@boatgeek and @Capt. Eric ... quick question on the electrical system. After Boatgeek's comment on the NTSB report, it seems like this whole problem started with some CBs popping on non-essential equipment....but, that were tied to critical equipment. It begs the question as to why aren't critical systems isolated from non-critical systems? Why is the ship's steering tied to some crew member's mini-fridge?

The initial blackout was from breakers tripping around the main high voltage-low voltage transformer, directly in the load path from the generators to critical systems. This part at least wasn't a case where something went wrong on the crew member's fridge and that cascaded up to critical equipment.

With that out of the way, non-essential equipment is powered from the same panels as essential equipment because you'd rather run the minimum possible number of generators for maintenance, efficiency, and other reasons. The non-essential equipment on this ship was likely on the order of 200-500 kW total load, and might be down around 30-50 kW at certain times of day. It doesn't make sense to run a small generator at 10%-90% load when you could just tack that power demand on to a 4 MW generator you're already running.

I don't know the specific power architecture of this ship, but on a US-flag ship you would likely see some variation on this kind of power architecture:

• Main generators feed a high voltage primary switchboard
• Primary switchboard has some high voltage feeds for high horsepower items (like the bow thruster) plus at least two feeds to transformers that supply the primary low voltage (440 VAC) switchboard
• The primary low voltage switchboard feeds 3 or more 440VAC power panels plus the emergency switchboard. You would expect to see critical items in the engine room (cooling pumps, fuel pumps, steering HPUs, etc.) in separate panels that are fed from each side of the bus tie breaker. That way, there's a better chance of one of those critical services surviving if there's a fault.
• One or two of those 440VAC panels feeds loads in the accommodations blocks, with things like the HVAC system and the range/ovens on 440. There would then be a step-down transformer to even lower voltage (on this boat probably 220VAC, on a US-standard, 208/120VAC three phase) for lights, the crew's fridge, etc.
• The emergency switchboard would feed emergency lights, an extra fire pump, bilge pump, steering HPU, lifesaving equipment, navigation electronics, and a variety of other loads. The emergency switchboard is normally connected to the main power system, but can be disconnected and fed from the emergency generator alone if main power goes out.

As part of the original design, the circuit breaker ratings and time-current trip curves should all be coordinated so that if a breaker trips on one load or panel it doesn't propagate further up the chain. So if the crew's fridge shorts out, it should trip the breaker in the panel it's connected to, but the breaker feeding that panel shouldn't trip. If you overload a panel, its breaker should trip, but not the one feeding the panel above, etc. Whether that coordination has survived over the past 15 years of operation depends a lot on how closely replacement parts match the originals and if other changes were made to the system.

One thing that I don't understand is why one couldn't have both transformers feeding the LV bus with the LV bus tie closed. I expect that there's an explanation involving circulating currents and not letting the magic smoke out, but I don't know enough to know what that is.

 

[boatgeek]

I would think that some of the crew members (especially officers) would want their own lawyers at some of these meetings as well. I wouldn't trust that my employer's lawyers wouldn't throw me under the bus at their earliest convenience.

Those guys can't afford lawyers.

There's no point in going after any of the crew civilly because they won't have enough money to be worth it. Nobody on that ship was a millionaire. The officers are probably ten thousandaires, but the crew probably aren't. It is very much in the company's interest to defend the crew from criminal action because if the crew is found guilty of criminal actions (which seems unlikely), it looks bad when the company defends itself from civil liability. And the company definitely wants to keep the crew on side because otherwise they can start saying things like "The central office told us to..." That kind of thing ratchets up the company's civil liability risk.

 

[cvanc]

By high voltage you mean the native output of the generators, correct? What is it?

Then a giant stepdown transformer whose secondaries feed the 440V 3 phase ship-wide distribution?

Here's where I prove I'm out of date by 40 years - I remember tons of old USN surplus and most of it ran on a 400Hz powerline. Are modern ships still 400Hz today? Thanks.

 

[boatgeek]

By high voltage you mean the native output of the generators, correct? What is it?

6600VAC

Then a giant stepdown transformer whose secondaries feed the 440V 3 phase ship-wide distribution?

There's at least the bow thruster at 6600VAC. I don't know if there are any other loads on the high voltage bus. But yes, most everything else would be on 440VAC or below, fed by a pair of transformers. Since it's foreign flag, you'd expect loads above ~1 kW to be 440 VAC, and smaller loads like lights and receptacles to be 220 VAC. US flag would typically be 480 VAC for larger loads and either 208/120VAC or 240/120VAC for smaller loads.

Here's where I prove I'm out of date by 40 years - I remember tons of old USN surplus and most of it ran on a 400Hz powerline. Are modern ships still 400Hz today? Thanks.

I would guess that since this is foreign flag they'd use 50 Hz. US commercial ships are 60 Hz. The Navy may still use 400 Hz, but not in any of the (very few) projects I've been involved in. Those projects have all been small boats where we're trying to use COTS stuff as much as possible.

Of course, motors driven by VFD controllers are at different frequencies, but you get the idea.

 

[Bravo52]

Finally, Bravo52 - note that pilots are advisors and are not responsible for a ship (with one exception, but that's a different subject). They will not have any culpability here, and in fact acted very well, and saved lives.

I'm sure there is case law that speaks to harbor Capts roles in mishaps but it's interesting that US law requires US pilots be in used during transit of harbor activities. Even as a role of an "advisor", is suspect there is some culpability. The US Capts' actions after the crash (one of many) is a good example of knowing what to do in different scenarios.

Ironically, it is likely the similar US law that may very well limit the liability of the carrier. Sadly, I suspect the personal injury lawsuits will be a lot easier to deal with than the liability associated with the bridge.

 

[boatgeek]

I'm sure there is case law that speaks to harbor Capts roles in mishaps but it's interesting that US law requires US pilots be in used during transit of harbor activities. Even as a role of an "advisor", is suspect there is some culpability. The US Capts' actions after the crash (one of many) is a good example of knowing what to do in different scenarios.

Terminology matters a lot here. The advisor is a pilot (who always* has a captain's license), but the captain is the ship's captain. The captain is always ultimately responsible for what happens on board. Pilots are required for local knowledge. The ship's captain may have 30 years of experience but may never have transited these waters before. The pilot knows the ins and outs of local weather, currents, tugs, etc.

In this case, just about all of the causes of the accident were outside the pilot's control, so the pilot almost certainly won't have any liability.

Ironically, it is likely the similar US law that may very well limit the liability of the carrier. Sadly, I suspect the personal injury lawsuits will be a lot easier to deal with than the liability associated with the bridge.

I think it's pretty likely that the carrier's management will be limited. The only good thing about that is that the ship and its cargo has some value after the accident. In a few cases that I've been involved in, the value after the accident was zero, so the shipowner had no liability.

* I think it's theoretically possible that a pilot wouldn't be a licensed captain, but I can't imagine the situation where that would happen. Pilot associations guard the reputation of their profession extremely jealously.

 

[Bravo52]

Terminology matters a lot here. The advisor is a pilot (who always* has a captain's license), but the captain is the ship's captain. The captain is always ultimately responsible for what happens on board. Pilots are required for local knowledge. The ship's captain may have 30 years of experience but may never have transited these waters before. The pilot knows the ins and outs of local weather, currents, tugs, etc.

Thanks for the clarety. Lots of terms being used and it is important to get them right.

 

[mikec]

I'm sorry, but I couldn't watch it after the first 2 minutes. All he was doing was reading the NTSB report, pretty much word for word.

In defense of Juan Brown, he's a former military and current airline pilot, knows what he's talking about in most cases, and isn't afraid to say when he doesn't know something. That said, yes, a lot of what he does is just read the report, and he admits he doesn't know much about ships. If you find that not to your taste, perfectly understandable. FWIW I got something out of it.

It's still not clear from the report why the breakers tripped in the first place, but they had trouble the day before and swapped sides on the breakers; that seems to be have been an indication of a major latent problem still not understood.

 

[Banzai88]

It's still not clear from the report why the breakers tripped in the first place, but they had trouble the day before and swapped sides on the breakers; that seems to be have been an indication of a major latent problem still not understood.

Breakers get less and less reliable the more they're activated, and as a natural aging process. That's why we have to pull, test, and often rebuild and recertify them with alarming regularity. My teams averaged about a thousand or so each year from small to huge main power breakers for USNS and a variety of civilian MSC vessels.

If that's not done, they will trip more and more often with smaller and smaller current spike transients. Transients such as a sudden load, or changes in power loading and supply from the main power buss.

Heck, even the switch to or from shore power, and the associated phase rotation shift that often occurs, is sometimes enough to pop a LOT of main supply breaker on the main buss and kick a lot of equipment off line.

Bring it back online in the wrong order, and it'll all pop offline all over again, ESPECIALLY if the load was never properly balanced to begin with.

Same thing with the equipment local control boxes. Relays age, contactors get dirty, connections vibrate loose.....you get the idea. In actual practice, none of it is nearly as robust as you might imagine it should be!

There's so much work in the ships that I literally made a mid 6 figure annual salary running contracts and teams to keep main power equipment clean, serviced, USCG certified, and operating properly......but it was 200+/- days a year on the road around the world.

 

[Capt. Eric]

Thanks for the clarety. Lots of terms being used and it is important to get them right.

OK, let's get into Pilots for a bit.

A pilot, as was said, is required on ships and hired for their "local knowledge" of the port and how things operate there. They also typically have great skill and experience in shiphandling (but to be honest, I have seen a few, very rare, exceptions to this).

A Pilot is not held responsible for most accidents a ship has because the pilot is not maintaining the ship. They don't know the crew, and the crew don't know them. Often the crew don't even speak the same language as the pilot. In essence, the pilot is an expert on the port, but the ship's Captain is supposed to be an expert on the ship itself. And the ship's Captain is answerable to the company and to all the other legal authorities.

Exceptions:
1. IF the Pilot, who is conning the vessel (giving the steering and engine orders, but with implied Captain's approval) gives improper orders or is negligent in his handling or advice to the ship, then he may be held responsible for that. But the Captain is supposed to realize when danger is approaching and head it off regardless. So a Pilot my get himself in trouble, but the Captain will typically carry the brunt of the fault. Yes, that can be unfair, but that's why they get the big bucks. (but pilot get paid a lot more)
2. Panama Canal. The Panama Canal is the only place in the world where the Pilot has actual legal authority over the maneuvering of the vessel beyond the ship's Master. What that means is if I am Captain going through the Canal, and the Pilot says "Hard Left" to the helmsman, but I say "NO! Hard Right" my helmsman had better do what the Pilot says and ignore me. If the pilot is wrong, the Canal will pay for the damages. If the Helmsman does what I tell him, I have got a serious problem, and in extreme cases, could be arrested in Panama. (The helmsman gets to go home)

Think that's messed up? Keep reading.

NOTE: A pilot does not always have a "Master's License" (which is what a Captain's license is called) and these days, usually does not. Ports have different ways of hiring and training their pilots, usually run by a "Pilot Association" or by a state Pilot Commission. There was a time when most pilots had master's licenses, but I think the opposite is true today (but never took a poll). These days a Pilot Association wants to train a person before he/she develops habits they want to break them of. Also, after spending a great deal of time and money training the person, they don't want them retiring in a few years. Better to keep them around for 20-30 years. So what I have seen lately is that associations are recruiting people with 2-5 years sailing experience (with some exceptions) and that are in their mid 20 to mid 30's. Typically these folks will have a second mate's license, or maybe a Chief Mate's license.

There are other types of pilots that are used in some ports. In some ports you get one or two pilots that take the ship from sea buoy to the dock. But some places they have a "Bar Pilot" who takes you from the Buoy to just inside the port proper or river. Then you might have a River pilot (like on the Mississippi or Columbia rivers) who takes you upriver some distance (perhaps changing out every few hours). Or maybe you have a Harbor Pilot that takes you through the rest of the port areas. And yet again, you could get a "Docking Pilot." That's the interesting one.

A Docking Pilot typically works for a tug boat company. They will join the ship a few hundred yards, or a few miles away, depending on where tugs are first alongside, and make the dock approach and moor the vessel. Most docking pilots have little or no sea time on ships at sea. They might, but that's mostly irrelevant. Most docking pilots come up through the ranks of the tug boat company. They handled tugs during docking of ships and learn ship handling from a very different perspective. They are, again, typically very good at what they do - shiphandling. But they will often just have a license that is limited to smaller vessels and tug boats, or limited in positions like 3rd or 2nd mate.

So what license gives them the authority? A pilot must sit for an exam that is part written (Rules of the road and navigation) and part "chart work". They are given a large blank sheet of paper and they actually draw the chart from memory. Every buoy, landmark, dock, channel, shoal, and light, as well as depth readings all over the area. This is what we call "difficult". Before they are even allowed to sit for the exam, they have to have transited the area they are testing for a certain number of times (I forget what that number is, but maybe 40 or 50 times). So now they have a pilot's license for that given area. Many ports, rivers or regions (like Puget Sound or Long Island Sound) are broken down into several areas. They have to test for all of them to pilot vessels throughout their territory.

But that doesn't even get you the job. You have to be accepted into the pilot association as an apprentice. An apprentice rides ships in and out and gradually is given more and more hands on experience as the "Full Pilot" trains them and gradually brings them up to speed. This process can be a year, or as many as 7 years in some old-school associations. Then they start on their own with the smaller ships, and gradually work their way up to the larger ones. Again, that can take a few years to do.

Some aspects of the above may surprise many of you reading this, but I can say that the end result is that 99.99% of pilots in the US are outstanding. I've met some pilots I didn't like, but in only one occasion in over 30 years did I meet a pilot in the US I thought was "not good." (He was soon after dismissed by his association) In other countries, it's a different story. Most are pretty good. Many are downright awesome. But every once in a while, you might come across one in some 3rd world backwater that just isn't equipped for the job. So I always had to be ready to step in and take over. Sometimes for one or two commands. Sometimes for much more. A couple of times I had actual arguments and thought I'd have to kick the guy off the ship. But we got through it. A few places the pilots don't come aboard until you've done all the hard stuff already. I could tell you a few stories, but this is gone on way too long as it is.

Good night everybody!

 

[Bravo52]

In defense of Juan Brown, he's a former military and current airline pilot, knows what he's talking about in most cases, and isn't afraid to say when he doesn't know something. That said, yes, a lot of what he does is just read the report, and he admits he doesn't know much about ships. If you find that not to your taste, perfectly understandable. FWIW I got something out of it.

It's still not clear from the report why the breakers tripped in the first place, but they had trouble the day before and swapped sides on the breakers; that seems to be have been an indication of a major latent problem still not understood.

Where Juan Brown excels is understanding NTSB reports. He may not be an expert on maritime crashes, but I would argue he is an expert on how to read NTSB reports and the culture that surrounds that agency. There are two types of "boards" in the Air Force. Accident Boards and Safety Boards. In very basic terms, Accident Boards are to find out what happened and assign fault. Safety Boards are similar in that they also discover causes but they are not attribution and for learning purposes only in order to better the force without fear of reprisal. Juan was trained in those areas and has an understanding of the process and how the NTSB conducts investigations. The good thing is it wasn't a "Dan Gryder" video...(that's a beer word).

 

[Bravo52]

Well, more good news in that they floated the Dali and moved/moving it back to pierside. Should be there by now. "They" said there was no damage to the hull (other than the topside stuff) and it moved right off with the help of 6 tugs. The transit was supposed to take a total of 21 hrs to float it, move it off the beach (so to speak) and push it to the pier. The push part was supposed to take 2.5 hrs as they were moving 2.5 miles @ 1MPH.

 

[boatgeek]

Well, more good news in that they floated the Dali and moved/moving it back to pierside. Should be there by now. "They" said there was no damage to the hull (other than the topside stuff) and it moved right off with the help of 6 tugs. The transit was supposed to take a total of 21 hrs to float it, move it off the beach (so to speak) and push it to the pier. The push part was supposed to take 2.5 hrs as they were moving 2.5 miles @ 1MPH.

If you go aground, you want to do it in mud. Even going really hard aground can end up with no damage to the hull.

 

[NTP2]

Well, more good news in that they floated the Dali and moved/moving it back to pierside. Should be there by now. "They" said there was no damage to the hull (other than the topside stuff) and it moved right off with the help of 6 tugs. The transit was supposed to take a total of 21 hrs to float it, move it off the beach (so to speak) and push it to the pier. The push part was supposed to take 2.5 hrs as they were moving 2.5 miles @ 1MPH.

Was anyone expecting damage? You can’t hurt that thing with a RPG!

 

[boatgeek]

Was anyone expecting damage? You can’t hurt that thing with a RPG!

Heh. It's amazing how much damage can be done to a grounded ship, even on a flat bottom. On a hard bottom, you can easily get a few thousand tons concentrated on a few tens of square feet of bottom. Bad things happen. Mud is good, since the ship sinks in and spreads the load. Sand isn't usually too bad. Gravel can get ugly.

If there are large rocks, it gets even worse. I've been involved in a few salvage/repair efforts on vessels that landed on rocky shores. They all ended up with holes several feet into the hull from boulders sitting on the beach, and they hit at relatively low speed. When the Costa Concordia went aground at speed, a rock on the bottom folded up 1" bottom plate like it was a stick of gum.

 

[NTP2]

Heh. It's amazing how much damage can be done to a grounded ship, even on a flat bottom. On a hard bottom, you can easily get a few thousand tons concentrated on a few tens of square feet of bottom. Bad things happen. Mud is good, since the ship sinks in and spreads the load. Sand isn't usually too bad. Gravel can get ugly.

If there are large rocks, it gets even worse. I've been involved in a few salvage/repair efforts on vessels that landed on rocky shores. They all ended up with holes several feet into the hull from boulders sitting on the beach, and they hit at relatively low speed. When the Costa Concordia went aground at speed, a rock on the bottom folded up 1" bottom plate like it was a stick of gum.

Wow 6 hours to abandon ship!!