Baltimore Bridge Collision and Collapse

[Art Upton]

Wow 6 hours to abandon ship!!

I suppose you have not seen this movie?

 

[Bravo52]

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.

 

[boatgeek]

Wow 6 hours to abandon ship!!

It was an absolute debacle of an emergency response. Among other things, the captain abandoned ship well before the passengers had all gotten off. Which led to this exchange between DeFalco (Italian Coast Guard) and Schettino (Costa Concordia's captain) after the captain was off the boat:

Schettino: "In this moment, the boat is tipping …"

De Falco: "I understand that, listen, there are people that are coming down the pilot ladder of the prow. You go up that pilot ladder, get on that ship and tell me how many people are still on board. And what they need. Is that clear? You need to tell me if there are children, women or people in need of assistance. And tell me the exact number of each of these categories. Is that clear? Listen Schettino, that you saved yourself from the sea, but I am going to … really do something bad to you … I am going to make you pay for this. Go on board, (expletive)!"

Schettino: "Commander, please …"

De Falco: "No, please. You now get up and go on board. They are telling me that on board there are still …"

Schettino: "I am here with the rescue boats, I am here, I am not going anywhere, I am here …"

De Falco: "What are you doing, commander?"

Schettino: "I am here to co-ordinate the rescue …"

De Falco: "What are you co-ordinating there? Go on board! Co-ordinate the rescue from aboard the ship. Are you refusing?"

Schettino: "No, I am not refusing."

De Falco: "Are you refusing to go aboard, commander? Can you tell me the reason why you are not going?"

Schettino: "I am not going because the other lifeboat is stopped."

De Falco: "You go aboard. It is an order. Don't make any more excuses. You have declared 'abandon ship'. Now I am in charge. You go on board! Is that clear? Do you hear me? Go, and call me when you are aboard. My air rescue crew is there."

Schettino: "Where are your rescuers?"

De Falco: "My air rescue is on the prow. Go. There are already bodies, Schettino."

Schettino: "How many bodies are there?"

De Falco: "I don't know. I have heard of one. You are the one who has to tell me how many there are. Christ!"

Schettino: "But do you realise it is dark and here we can't see anything …"

De Falco: "And so what? You want to go home, Schettino? It is dark and you want to go home? Get on that prow of the boat using the pilot ladder and tell me what can be done, how many people there are and what their needs are. Now!"

There's a little more here. It's magnificent and all happened over open radio frequencies.
https://www.theguardian.com/world/2012/jan/17/costa-concordia-transcript-coastguard-captain

 

[boatgeek]

To illustrate what happens when a boat sits on a rock, these photos are from a barge that ran aground and more or less pivoted on top of a boulder over a week or so of tide cycles. The dent you see here was about 4 feet deep.



Looking at it from another direction. The red arrow points at a 14" deep I beam (~110-120 pounds per foot, so it's a lot of steel) that used to be straight. The bottom plate is 5/8" thick and was cleanly torn in several places. The blue arrow points at a primary bottom frame, 1" wide x 12" deep that buckled sideways. Rocks (and icebergs, thanks @Bravo52) are very unpleasant if your ship hits them. Mud is much preferred.

 

[Capt. Eric]

To illustrate what happens when a boat sits on a rock, these photos are from a barge that ran aground and more or less pivoted on top of a boulder over a week or so of tide cycles. The dent you see here was about 4 feet deep.

View attachment 646193

Looking at it from another direction. The red arrow points at a 14" deep I beam (~110-120 pounds per foot, so it's a lot of steel) that used to be straight. The bottom plate is 5/8" thick and was cleanly torn in several places. The blue arrow points at a primary bottom frame, 1" wide x 12" deep that buckled sideways. Rocks (and icebergs, thanks @Bravo52) are very unpleasant if your ship hits them. Mud is much preferred.

View attachment 646194

Yeppers! Been in the mud a couple of times (third world countries suck). No one ever read about it. A few times I was even congratulated for a job well done! (once was running the ship on the beach to be scrapped)

As for evacuating large cruise ships... It's a nightmare scenario that almost never ends well. Note that the Concordia happened in the very best of circumstances (close to shore of a modern maritime nation in perfect weather and shallow water with nothing else going on like a fire). Still, over 30 people died. Personally, I avoid cruise ships for various reasons. Poor emergency response is one. Not that it is always the crew's fault. It's just a major challenge to handle an event like that.

 

[MClark]

When I was a kid (like 6) we lived in Seattle. Some big ship had been grounded on the coast and we went to see it.
Blown onto big rocks and after a week it was broken in half, one part on its side and full of sand.
Was the 1960’s so we could walk down the beach right up to the wreck. Huge!
No security, no one cared.

 

[Capt. Eric]

When I was a kid (like 6) we lived in Seattle. Some big ship had been grounded on the coast and we went to see it.
Blown onto big rocks and after a week it was broken in half, one part on its side and full of sand.
Was the 1960’s so we could walk down the beach right up to the wreck. Huge!
No security, no one cared.

Those were the good old' days when you could do almost anything as long as you were surrounded by water. By the time I retired in 2020, you couldn't use the head without a checklist, risk assessment, and logging it in the "international crapper logbook."

Ok, I might be exaggerating slightly, but really not as much as you'd think.

 

[bjphoenix]

Heh. It's amazing how much damage can be done to a grounded ship, even on a flat bottom.

I know a lot about building design including bending of metal shapes but I don't know much about ship design. I've been watching videos of Battleship New Jersey in drydock, the ship is setting on a grid of wood and concrete blocks. I suppose if it can set on water then it can set on blocks distributed in the right pattern. That ship has approximately 40' draft so the water pressure underneath is around 2400 psf. This is a drop in the bucket compared to bearing pressure under buildings. I don't recall what they said the bearing pressure was on the blocks under the battleship, I'm guessing maybe 15000 psf. I don't know how they get the pattern of blocks correct heightwise to conform to the shape of the hull but with the right shape of blocks the pressure would be distributed nicely under the hull. Run the ship onto a big blob of mud and after the mud gets out of the way the pressures could be distributed pretty well. Mud is not particularly strong but probably exerts more pressure on the hull while it is being pushed out of the way. Now with something harder than mud the forces/pressures can be very high since it can all concentrate on a small area. Regarding the battleship- there are some places where the hull plating is fairly thin, I think they said 1/2". Under the pressure of the blocks I think 1/2" plate can only span about 9" between supports. This seems kind of short to me.

 

[boatgeek]

I know a lot about building design including bending of metal shapes but I don't know much about ship design. I've been watching videos of Battleship New Jersey in drydock, the ship is setting on a grid of wood and concrete blocks. I suppose if it can set on water then it can set on blocks distributed in the right pattern. That ship has approximately 40' draft so the water pressure underneath is around 2400 psf. This is a drop in the bucket compared to bearing pressure under buildings. I don't recall what they said the bearing pressure was on the blocks under the battleship, I'm guessing maybe 15000 psf. I don't know how they get the pattern of blocks correct heightwise to conform to the shape of the hull but with the right shape of blocks the pressure would be distributed nicely under the hull. Run the ship onto a big blob of mud and after the mud gets out of the way the pressures could be distributed pretty well. Mud is not particularly strong but probably exerts more pressure on the hull while it is being pushed out of the way. Now with something harder than mud the forces/pressures can be very high since it can all concentrate on a small area. Regarding the battleship- there are some places where the hull plating is fairly thin, I think they said 1/2". Under the pressure of the blocks I think 1/2" plate can only span about 9" between supports. This seems kind of short to me.

Drydocking is its own special area of expertise. The block bearing pressures are largely limited by the strength of the blocks themselves since you always put the blocks where structure backs up the shell plate. As you saw above, you can't load up the plate between frames very much before you start denting the plate in. The Navy limits block pressures to 20 long tons/square foot, or just under 45,000 psf. That's a really high load, and you try to keep it lower than that by using more blocks if you can. Most ships are also built with a centerline keel that is especially strong, in part for drydocking. Typically, the line of blocks on centerline will carry 60%+ of the weight of the ship. The blocks off to the sides are mainly to keep the ship from tipping over. The larger the ship is and the more flat bottom it has, the more weight will be carried by blocks on longitudinal bulkheads parallel to centerline but offset to either side.

Most ships will have a docking plan that shows where to place blocks, where the structure is, and the hull shape that the blocks need to meet. The blocks are then built up to the required height (if you can't get enough blocks on the flat bottom, that is). The docking plan will also show anything you don't want blocks under (transducers, water inlets and discharges, coolers that are outside the hull, etc.).

Navy ships are their own animal because they're also built for shock loading as well as sea pressures. For most commercial boats and ships, the frame spacing on the shell is on the order of 24"-30". There's some exceptions like really small boat, icebreakers, and the like.

 

[bjphoenix]

Drydocking is its own special area of expertise. The block bearing pressures are largely limited by the For most commercial boats and ships, the frame spacing on the shell is on the order of 24"-30". There's some exceptions like really small boat, icebreakers, and the like.

I understand how the internal framing could transfer the weight more directly to the blocks. So if the plates themselves don't have to carry this load then they only carry the water pressure itself. That agrees better with 1/2" plates, 40' of draft and 24" frame spacing.

 

[Capt. Eric]

Drydocking is its own special area of expertise. The block bearing pressures are largely limited by the strength of the blocks themselves since you always put the blocks where structure backs up the shell plate. As you saw above, you can't load up the plate between frames very much before you start denting the plate in. The Navy limits block pressures to 20 long tons/square foot, or just under 45,000 psf. That's a really high load, and you try to keep it lower than that by using more blocks if you can. Most ships are also built with a centerline keel that is especially strong, in part for drydocking. Typically, the line of blocks on centerline will carry 60%+ of the weight of the ship. The blocks off to the sides are mainly to keep the ship from tipping over. The larger the ship is and the more flat bottom it has, the more weight will be carried by blocks on longitudinal bulkheads parallel to centerline but offset to either side.

Most ships will have a docking plan that shows where to place blocks, where the structure is, and the hull shape that the blocks need to meet. The blocks are then built up to the required height (if you can't get enough blocks on the flat bottom, that is). The docking plan will also show anything you don't want blocks under (transducers, water inlets and discharges, coolers that are outside the hull, etc.).

Navy ships are their own animal because they're also built for shock loading as well as sea pressures. For most commercial boats and ships, the frame spacing on the shell is on the order of 24"-30". There's some exceptions like really small boat, icebreakers, and the like.

Just to add a bit on the subject. I was never crazy about shipyards, however the dry docking process is long, but kind of interesting.

All ships should have the docking plan. It is probably the most important item to give to the shipyard before a drydocking. There will be copies on board, and in the company's office. Using that, the yard will arrange the blocks as indicated by the plan just as boatgeek says. When bringing the ship into the dock, you obviously have to position it perfectly using mooring lines. Sometimes lines or long sticks are used to measure from the sides, front or back of the dock. (Yeah, maybe lasers can be used, but a bamboo stick is as accurate as needed, and a lot cheaper) Often divers will go down to confirm the position. They also look for blocks that may fall over from bringing the ship in. One or two is no big deal. Lose too many and we have a 12hr delay and more ship maneuvering while they empty the dock and fix the arrangement. That's bad. Then a little water is pumped out so the ship is touching the blocks. Divers might check it again at this point. Then more water is pumped out so the ship is firmly on the blocks, but still in water. Time to transfer services. Hook up electric to the shore power and shut down the ship generators, water pumps, coolers and other water dependant equipment. The ship gets very quiet and there's no more vibration. Very strange feeling. Then pump out the water until the ship is dry. Meanwhile, start pumping the ballast tanks out, if you have the power for that. If not, open the valves and let gravity drop it all out. Once you can walk onto the dock floor, you take a look for any surprises. Dents or snagged fishing nets and so on. It happens. Finally, you pull the plugs. Yes, plugs. Every bottom tank has a plug, and they pull the ones for water ballast tanks to let the last few inches drain out for inspections. All the above can take from 6 to 10 hours. Then the real shipyard work starts.

 

[Capt. Eric]

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

Oh, and yes you can! You just gotta know where to put it. (No, I'm not telling.)

 

[boatgeek]

Oh, and yes you can! You just gotta know where to put it. (No, I'm not telling.)

Being all realsies here, an RPG will go through the hull anywhere on the ship, and on any ship but a battleship and possibly an icebreaker. It won't sink the ship, or in most places even keep it from sailing on, but it'll ruin everyone's day. There are a few spots where you could disable the ship (and no I won't tell, though it should be pretty obvious). However, no matter how many RPGs you have, it would be hard to sink it. If you'll indulge me in another sea story...

In 1999, the New Carissa ran aground (in sand!) on a beach in Oregon. Before they could get her refloated, the ship broke in two at the front of the house. Salvors eventually managed to get the bow refloated, and after losing it back on the beach once, the salvors got it far enough offshore to sink it. The ship was then turned over to the Navy for target practice. 400 lbs of high explosives didn't sink the ship. 69 5" rounds from a destroyer didn't do the job either. A single torpedo from a sub finished it off in 10 minutes. I'm sure the surface fleet got a lot of ribbing from the sub fleet after that.

This is an extremely abridged version of the story--the whole saga is worth reading at the Wikipedia page linked above.

 

[NTP2]

Oh, and yes you can! You just gotta know where to put it. (No, I'm not telling.)

who do you take me for?! I’m not a criminal! I’m simply a structural safety inspector

 

[NTP2]

In 1999, the New Carissa ran aground (in sand!) on a beach in Oregon. Before they could get her refloated, the ship broke in two at the front of the house. Salvors eventually managed to get the bow refloated, and after losing it back on the beach once, the salvors got it far enough offshore to sink it. The ship was then turned over to the Navy for target practice. 400 lbs of high explosives didn't sink the ship. 69 5" rounds from a destroyer didn't do the job either. A single torpedo from a sub finished it off in 10 minutes. I'm sure the surface fleet got a lot of ribbing from the sub fleet after that.

This is an extremely abridged version of the story--the whole saga is worth reading at the Wikipedia page linked above.

They practically built a drill rig just to remove a stern!!

Ps I’ll never get tired of sea story’s, they are always informative!

 

[Capt. Eric]

Being all realsies here, an RPG will go through the hull anywhere on the ship, and on any ship but a battleship and possibly an icebreaker. It won't sink the ship, or in most places even keep it from sailing on, but it'll ruin everyone's day. There are a few spots where you could disable the ship (and no I won't tell, though it should be pretty obvious). However, no matter how many RPGs you have, it would be hard to sink it. If you'll indulge me in another sea story...

In 1999, the New Carissa ran aground (in sand!) on a beach in Oregon. Before they could get her refloated, the ship broke in two at the front of the house. Salvors eventually managed to get the bow refloated, and after losing it back on the beach once, the salvors got it far enough offshore to sink it. The ship was then turned over to the Navy for target practice. 400 lbs of high explosives didn't sink the ship. 69 5" rounds from a destroyer didn't do the job either. A single torpedo from a sub finished it off in 10 minutes. I'm sure the surface fleet got a lot of ribbing from the sub fleet after that.

This is an extremely abridged version of the story--the whole saga is worth reading at the Wikipedia page linked above.

I remember that mess!

There have been many a ship that breaks in half for various reasons and one or both halves stay floating for a considerable amount of time. Like days, weeks, months. These days someone will usually either tow if for salvage or someone will sink it. Back in days of sail, they gave raise to the whole "ghost ship" thing. Much of course depends on the ship type and cargo, if any.

 

[James Duffy]

He may know airplanes, but no, a ship is not at all like an airplane.

Several years ago I attended a presentation by John Goglia, an aviation maintenance expert and former member of the NTSB Board. He's a fascinating guy, and one of the surprising things he shared is that the board goes out of their way to have board members investigate accidents outside their sphere of specialization. His first investigation after being appointed to the Board was a train accident, for instance. He defended the practice, noting that people will ask more critical questions when outside of the comfort of their domain, and that transportation accidents universally seem to follow a chain of errors rather than a single mistake.

 

[Capt. Eric]

Several years ago I attended a presentation by John Goglia, an aviation maintenance expert and former member of the NTSB Board. He's a fascinating guy, and one of the surprising things he shared is that the board goes out of their way to have board members investigate accidents outside their sphere of specialization. His first investigation after being appointed to the Board was a train accident, for instance. He defended the practice, noting that people will ask more critical questions when outside of the comfort of their domain, and that transportation accidents universally seem to follow a chain of errors rather than a single mistake.

All that I agree with, although those guys are usually given some cross training in what they are investigating, and/or they are assigned a very specific aspect to hone in on. You do need to have some board members who are very familiar with the subject so that they know what questions to ask. Sometimes you have to know what you don't know to get to the bottom of something.

If you weren't familiar with ships, and how they are run, I could point to all kinds of nice looking positive things that we do. But a "real" ship guy would see that, and turn around to ask me about "silly little things" like who maintains the ventilation cover hold down bolts that prevent a space from flooding during heavy weather when waves are on deck. Or, "Ok, your hatch covers look great, but there is a lot of gouging around the base of the hatch coaming. What have you done to address that?" Or an experienced guy would say he doesn't need to look through the entire ballast tank, he just wants to see the section assembly joint that runs through it (where ship sections are joined/welded together they are stressed more and tend to rust faster). Saves us all a lot of tank crawling and gets to the concerns faster.

More than once I have gone through inspections by "officials" that don't know what they are looking at. I hated it. Often you can skate past the small issues, which is nice. But sometimes a know-nothing latches onto some stupid thing and thinks it/you are a problem when it honestly isn't. He just doesn't know what he's looking at. And he can make a major headache over it.

Also, that's fine for an investigator where they are seeking answers. Keeps the investigators looking broadly, and not putting blinders on. What I am not fond of is where some people have a blog or youtube channel and claim to be an expert in something when they are not. I would never tell you what a NTSB report about an airplane accident is all about. I've read a couple dozen NTSB reports, but airplanes are not my wheelhouse. Obviously I know a bit about ships so I will try to answer any questions that come up here on this subject. I know general engineering practices on a ship since I worked with many engineers, but I am not an engineer, so I won't try to get too technical on some of those questions, like why the breakers tripped. I could guess, but I don't have the detailed knowledge to give you a real answer. And I know what happens on "many" ships, but I wasn't on the Dali, so I can't tell you exactly what happened. Just what was supposed to happen or what should have happened, or what usually would happen. Sometimes I can even say what "appears to have" happened.

There's a difference between someone who is helping people understand a subject, and people who are trying to impress others with how smart they think they are. Beware of anyone who tells you they know, when they were not there at the given time and place.

 

[cls]

one of the surprising things he shared is that the board goes out of their way to have board members investigate accidents outside their sphere of specialization.

I instantly thought of the Challenger accident board... Feynman, putting salt on the ice water, then putting o rings in, and pulling them apart... On live TV.

Not a rocket subject matter expert, but just the clarity of common sense.

 

[boatgeek]

More than once I have gone through inspections by "officials" that don't know what they are looking at. I hated it. Often you can skate past the small issues, which is nice. But sometimes a know-nothing latches onto some stupid thing and thinks it/you are a problem when it honestly isn't. He just doesn't know what he's looking at. And he can make a major headache over it.

The worst is the "long blue tail." That's when you're doing something with the local Coast Guard folks and they need to get several people trained on it so you have the lead person and 6 trainees. I don't have anything against trainees--I usually like to be the one explaining why we do things the way we do so that they look at our work as the gold standard. However, they often start looking around and asking questions that can derail the time-sensitive thing I'm trying to do. Sometimes you end up explaining why it doesn't matter to this 2,000-ton ship's stability that the mop is on this deck and not that deck. I wish I were making that up. Once or twice, I've asked that they ask their senior person the questions instead of me so I could focus on my job.

 

[Capt. Eric]

The worst is the "long blue tail." That's when you're doing something with the local Coast Guard folks and they need to get several people trained on it so you have the lead person and 6 trainees. I don't have anything against trainees--I usually like to be the one explaining why we do things the way we do so that they look at our work as the gold standard. However, they often start looking around and asking questions that can derail the time-sensitive thing I'm trying to do. Sometimes you end up explaining why it doesn't matter to this 2,000-ton ship's stability that the mop is on this deck and not that deck. I wish I were making that up. Once or twice, I've asked that they ask their senior person the questions instead of me so I could focus on my job.

Oh, I hear you! Been there, done that 3-ring circus. I love an annual with 6 or 7 inspectors while cargo is going on and a new crew just coming aboard. They want to see everything since it's a training exercise, but we're all busy, half or more of the crew are clueless, and it all has to be done in 4 hours. Inconceivable!

One of my favorite USCG Trainee stories: They're doing a document check during annuals. The youngster asks for all the personnel documents (licenses, stcw, physicals, etc). So I hand him my NJ state safe boating card. The kid is trying to act all serious. Turning it over back and forth for like a minute and a half looking for where it says "USCG" or "Master". His senior blue suit is dying. I'm on to other questions from another guy, but watching him too. Finally I couldn't stand it anymore and ask him, "Anything wrong?" He looks at me and says "I don't see where it says 'Master' on here?" The senior guy and I just start cracking up.

It was actually a good ice breaker and the kid relaxed after that. We spent a lot of time together that day and he learned a lot, which is good. My investment in making a better USCG inspector.

 

[Capt. Eric]

The worst is the "long blue tail."

My longest tail was a day when we were breaking out from a 6 month layup. On the first full day we have annuals (6 or 7 man team), closing out an investigation on an engine casualty from months ago (3 man team). Then while putting away paint, a guy drops a 5-gal can, it breaks open and runs down the scupper into the water. So we dutifully report it and another 4 man team shows up. Plus we had ABS there for surveys and audits. And we were starting cargo loading. That was a very long, very busy day.

For those who don't know, it's like having the police show up on your lawn at 7am with 15 officers, investigating 4 different crimes.
(Or an average day at Mar-a-Lago)

 

[boatgeek]

One of my favorite USCG Trainee stories: They're doing a document check during annuals. The youngster asks for all the personnel documents (licenses, stcw, physicals, etc). So I hand him my NJ state safe boating card. The kid is trying to act all serious. Turning it over back and forth for like a minute and a half looking for where it says "USCG" or "Master". His senior blue suit is dying. I'm on to other questions from another guy, but watching him too. Finally I couldn't stand it anymore and ask him, "Anything wrong?" He looks at me and says "I don't see where it says 'Master' on here?" The senior guy and I just start cracking up.

My favorite in that line was on a Russian boat we were working on. In the late 90's a bunch of Russian fishing boats came over to Seattle to take advantage of the newly open relationships to get decent paint and modern fishing equipment. So the Russian Registry surveyor comes down and asks that the drawings be stamped. "What kind of stamp?" "Stamped." So the mate goes back to his stateroom, pulls a Cap'n Crunch stamp out of the cereal box, and stamps the drawing. "Da, all good." I'm not sure how many bottles of booze changed hands on those jobs, but I'm pretty sure it wasn't single digits.

My longest tail was a day when we were breaking out from a 6 month layup. On the first full day we have annuals (6 or 7 man team), closing out an investigation on an engine casualty from months ago (3 man team). Then while putting away paint, a guy drops a 5-gal can, it breaks open and runs down the scupper into the water. So we dutifully report it and another 4 man team shows up. Plus we had ABS there for surveys and audits. And we were starting cargo loading. That was a very long, very busy day.

A paint spill with Coast Guard on board! That's always fun. The best I have on that is when we were just starting up a stability test and the crane blew a hose, dropping a few dozen gallons of hydraulic oil into the ship canal. That ended the test for the day.

 

[bjphoenix]

If you weren't familiar with ships, and how they are run, I could point to all kinds of nice looking positive things that we do. But a "real" ship guy would see that, and turn around to ask me about "silly little things" like who maintains the ventilation cover hold down bolts that prevent a space from flooding during heavy weather when waves are on deck

Similar in other disciplines- I have to know what problems to look for when I'm looking at construction drawings for buildings.

That's an interesting story about the New Carissa. By coincidence I was watching a documentary a couple of days ago about the Cruiser Independence during WWII and how it was hit by 2 torpedos and sunk very quickly. Apparently the first torpedo punched a pretty big hole in the front part of the ship where there is relatively light armor. And it's interesting to hear about ships breaking into multiple pieces. I can somewhat relate- the water pressure under the ship is somewhat constant front to back, if one end of a ship runs up on ground then there is more force on the end of the ship providing a bending force along the length of the ship wanting to break it in half if there are any planes of weakness. Many years ago, maybe 25 years ago, I worked with a guy who had served on a nuclear sub. He said that modern torpedos are designed to not hit the side of the ship but to go under it and explode, creating a void that causes the ship to break in half at the location. I had not heard that before.

One of the youtube channels that I watch occasionally is about the Battleship New Jersey.. That ship is in drydock now getting repairs done, it seems that a lot of deterioration can happen while the ship is sitting in the water year after year. I wondered why a museum ship didn't stay in its own drydock all year, and if necessary for appearance a structure could be built around the ship at water line as a fake water body to make the ship look like it was floating. Several of the videos have said that ships can't do that, without water pressure acting on the sides they will "pancake" with the upper decks coming down and the sides bowing out. As a structural engineer I can't see how that would happen with a steel ship but I can't question their knowledge about ships that I don't know anything about.

 

[Capt. Eric]

Similar in other disciplines- I have to know what problems to look for when I'm looking at construction drawings for buildings.

That's an interesting story about the New Carissa. By coincidence I was watching a documentary a couple of days ago about the Cruiser Independence during WWII and how it was hit by 2 torpedos and sunk very quickly. Apparently the first torpedo punched a pretty big hole in the front part of the ship where there is relatively light armor. And it's interesting to hear about ships breaking into multiple pieces. I can somewhat relate- the water pressure under the ship is somewhat constant front to back, if one end of a ship runs up on ground then there is more force on the end of the ship providing a bending force along the length of the ship wanting to break it in half if there are any planes of weakness. Many years ago, maybe 25 years ago, I worked with a guy who had served on a nuclear sub. He said that modern torpedos are designed to not hit the side of the ship but to go under it and explode, creating a void that causes the ship to break in half at the location. I had not heard that before.

One of the youtube channels that I watch occasionally is about the Battleship New Jersey.. That ship is in drydock now getting repairs done, it seems that a lot of deterioration can happen while the ship is sitting in the water year after year. I wondered why a museum ship didn't stay in its own drydock all year, and if necessary for appearance a structure could be built around the ship at water line as a fake water body to make the ship look like it was floating. Several of the videos have said that ships can't do that, without water pressure acting on the sides they will "pancake" with the upper decks coming down and the sides bowing out. As a structural engineer I can't see how that would happen with a steel ship but I can't question their knowledge about ships that I don't know anything about.

One problem with keeping a ship in perpetual dry dock is that it is extremely expensive to build a dry dock that will only be used once. They have done it on occasion. I think the Curry Sark in London (?) is dry. HMS Victory either is, or they are considering it I recall. But to afford such an undertaking really takes government help. In England they have a much stronger appreciation for Maritime history and industry. The US struggles with that. The battleship Texas was considering going to a permanent drydock. They tried to find the $100million estimated funding to just build the dock and couldn't get it.
I'm a member of the National Maritime Historical Society (http://seahistory.org/) and a big focus is to try to help maritime museums and historical ships stay alive by bringing attention to maritime history and their struggles. In the US, very little government money goes to those museums, and they are very expensive to maintain.

Structurally speaking, I think Boatgeek might be able to answer that better, but I wouldn't think it's a problem. But putting it on land doesn't solve all the problems. The steel will still rust, but you do have easier access to the paint. And flooding is less of a concern.

 

[boatgeek]

One of the youtube channels that I watch occasionally is about the Battleship New Jersey.. That ship is in drydock now getting repairs done, it seems that a lot of deterioration can happen while the ship is sitting in the water year after year. I wondered why a museum ship didn't stay in its own drydock all year, and if necessary for appearance a structure could be built around the ship at water line as a fake water body to make the ship look like it was floating. Several of the videos have said that ships can't do that, without water pressure acting on the sides they will "pancake" with the upper decks coming down and the sides bowing out. As a structural engineer I can't see how that would happen with a steel ship but I can't question their knowledge about ships that I don't know anything about.

That's more an issue with wooden boats than steel ones. Steel ships are remarkably flexible, though. The 438' barge that I designed and just launched can be expected to flex ~4-5" over its length depending on the load. Once you get to container ships with the big open hatches, the flex can be a foot or more.

Old wooden ships will get deformed (usually hogging, with the ends drooping down and the middle rising up) from their own weight and buoyancy distribution.

 

[Capt. Eric]

That's more an issue with wooden boats than steel ones. Steel ships are remarkably flexible, though. The 438' barge that I designed and just launched can be expected to flex ~4-5" over its length depending on the load. Once you get to container ships with the big open hatches, the flex can be a foot or more.

Old wooden ships will get deformed (usually hogging, with the ends drooping down and the middle rising up) from their own weight and buoyancy distribution.

Ships flexing. Another rabbit hole!

A ship the size of Dali will flex quite a bit. Tankers and bulk ships are very flexible. When working in a good rolling sea you can easily see it when standing on the deck looking down the length of the ship. Pipelines have dresser couplings and expansion joints or u-shaped features to allow for this, and you actually see the pipes expanding and contracting a few inches. And the ship gets loud with all the creaking and groaning. If you slam into a big wave (which you try to avoid, but happens from time to time) the whole ship will flex up and down at the ends like a long pvc pipe does as you walk through Home Depot.

 

[dr wogz]

some history worth reading regarding ship wrecks... This one in particular..

The song is a Canadian classic / legend..

https://en.wikipedia.org/wiki/SS_Edmund_Fitzgerald

 

[bjphoenix]

That's more an issue with wooden boats than steel ones. Steel ships are remarkably flexible, though. The 438' barge that I designed and just launched can be expected to flex ~4-5" over its length depending on the load. Once you get to container ships with the big open hatches, the flex can be a foot or more.

5" isn't much for 438' length. If I designed a building roof to span 438' it could be expected to deflect a lot more than that under full loading. However the thing to understand is a building roof structure of that span might be only 30' deep, the ship is a lot deeper than that and gets more stiffness just by virtue of its depth.
The biggest floating vessel I've been on while actually moving was a ferry across Lake Powell, probably only 100' long and with very smooth water. I would probably perceive a large vessel on rough seas to be very disconcerting if it is creaking and groaning and I'm seeing obvious deflection from end to end. People who do that for a living likely wouldn't think anything about it. We were designing a fancy metal building many years ago, essentially a large metal barn with some offices and brick on the outside. With brick you have to be more concerned about how much the building deflects in the wind, if it is just a barn you don't worry about it so much. My boss at the time said "the barn moves in the wind, the cows don't even look up".

 

[boatgeek]

5" isn't much for 438' length. If I designed a building roof to span 438' it could be expected to deflect a lot more than that under full loading. However the thing to understand is a building roof structure of that span might be only 30' deep, the ship is a lot deeper than that and gets more stiffness just by virtue of its depth.

As it happens, that barge was 25' deep. Deciding what span is for a structure with distributed loads and distributed supports is an interesting job, too.

The biggest floating vessel I've been on while actually moving was a ferry across Lake Powell, probably only 100' long and with very smooth water. I would probably perceive a large vessel on rough seas to be very disconcerting if it is creaking and groaning and I'm seeing obvious deflection from end to end. People who do that for a living likely wouldn't think anything about it. We were designing a fancy metal building many years ago, essentially a large metal barn with some offices and brick on the outside. With brick you have to be more concerned about how much the building deflects in the wind, if it is just a barn you don't worry about it so much. My boss at the time said "the barn moves in the wind, the cows don't even look up".

Several years ago, I was at a convention for passenger boat operators in Chicago. Naturally, we all went out on a boat ride up the river and out on to the lake. It was a ~120-foot boat and the waves were running 2-3 feet, so the boat was definitely moving, but not a lot by my standards. The folks that operate on inland rivers were much more uncomfortable.

It's surprising how little heel it takes to make you uncomfortable. Most people will notice about half a degree of heel. 2-3 degrees is very noticeable, especially if it's static (ie not rolling back and forth). 7 degrees of static heel feels very wrong, and non-mariner passengers will start panicking at 10-12 degrees. If the boat is rolling back and forth, you'll see people getting seasick around 5 degrees and getting freaked out at around 15 degrees. Of course, for professionals (especially on small boats) 10 degrees of roll to each side is an average day at the office and 20 degrees is rough but not abnormal.