WHY DON'T CRUISE SHIPS TIP OVER? | An introduction to ship stability 

Thanks for the comments SeaProf. I know there are plenty of technical videos for mariners to learn from, so I wanted to create something for everyone else. I am pleased that the video has come across as intended and will be useful to your class.

I am a mechanical design engineer Sir during the 1st case that means When tilting occurs due to any force.. definitely some parts of ship from lower area(under water) will come to upward from water, so CG must change from its mean line towards the max weight(max surface area apparently) but in this video ships CG is not changing from its mean position at all. Is that possible ? Sir please explain me ....

Thanks Sunil. The CG is the average position of all the masses onboard. Unless any of the masses within the vessel move, the CG cannot move. Applying an outside force does not affect the CG. Only adding or moving mass within the vessel can change the CG.

The Casual Navigator Well you have to count in slushing to the centre of gravity too, but on passenger ships that usually doesnt change too much. Overall, this is a great video to explain in a nutshell to non mariners how it works, and a great video for maritime students to learn the very basics before jumping into further forces and graphs.

Thanks SportSoulLife. That was the aim for this video so I am pleased it has come across that way.

In reality, yes, a 10kg weight would make no noticeable difference. It did suffice for the diagram though

Its just an Example .. Lol

Must be a toy ship

That said, this example ship doesn't seem to have much safety margin to compensate for things like big waves or ice/hail/sleet/snow accumulating on the upper decks (especially if that stuff is coming preferentially from one side).

Now if we can just apply this cruise ship technology to all ships and boats.

It is true that the everyone aboard will feel uncomfortable a long time before the ship is actually unsafe.

I used to be terrified of canoes cause they feel so tippy. One day my dad said "son, lets both go put life jackets on, push the canoe out from the dock a bit and purposefully tip it over". Okay. So we did. And once I did it for myself i realized how HARD it is to tip a canoe, and they don't scare me anymore at all. :D

Disney cruises also give you child molestation, people being thrown overboard, stabbings, theft and plenty more without even a policeman on board. Plus the added bonus of crappy characters that nobody really wants as an adult. I suffered through Disney as a child and didn't realise that the crap continues today. I think I would rather do time in a padded cell.

@@shed7614 wait... were you molestedereded on a cruise ship?

james braselton You okay there mate?

Lucky for Sweden today but a disaster in its day in the sun.

A high center of gravity with a high structure above the waterline and 2 levels of cannons. A shallow hold with not enough ballast. A short light keel. The problems were correctable...but the king was impatient.

@@jorgensenmj and lose cannons high up taking the center of gravity outside the center of bouancy.

Or the builders of the German ocean liner the SS Emperator/ RMS Berengaria

The lucky buggers went over in shallow water at least. Mary Rose wasn’t that lucky.

Aricstylegaming lol,

Like my sister.

@@chado3000 has nothing to do with spelling...Which is the correct terminology?... is what I'm asking

It's big brain time

Well you saved me 5 minutes of my time

Thanks Voitto. I hadn't thought of it like that before, but your way does explain centre of buoyancy very well.

That is a perfect description of center of bouyancy, I think. I know doodle-squat about ships, but I understand physics.

Yeah, I think that's right, but it is also the geometrical center of the cross-section. If you could print on cardstock the cross-section of the hull at the waterline and below, then the center of that would be where you could balance it on the point of a pin/pen.

@@GregConquest You're both right. As the displaced water has a constant density the geometrical center of the cross section is also the center of gravity. If for example the density of the water would change with increasing depth Voitto Kotiahos definition would still be correct though.

It is, literally, Archimedes' principle: "A body at rest in a fluid is acted upon by a force pushing upward called the buoyant force, which is equal to the weight of the fluid that the body displaces. If the body is completely submerged, the volume of fluid displaced is equal to the volume of the body."

Why ships float. Why ships don't tip over. Two different subjects.

@@jorgensenmj it explained both

“Ships don’t sink” Costa Concordia, the most recent sunken ship: “And that, I refuse to believe.”

@@sirankleknocker3122 it had many reason for sinking and it also didn't sank it was only half sank

This deserves many more likes

Going to guess that 's an Italian cruise ship captain.

madrx2 *CostaConcordia.exe has stopped working*

@@pgtmr2713 Costa Concordia

@@mirzaahmed6589 Yep

madrx2 and was last seen in a cafe on shore ordering a Peroni.

Epic a seafarer teaches a landlubber to be fearless

maybe this is just a ship model 😂😂😂

10 kilos of nails

Lol

Thanks Ian. I appreciate the remarks and am glad you liked the video.

Ian Patterson *_landlubber_*

Buoyancy = the weight of the water beig displaced. When an object weighs 2 kg, but pushes aside 3kg of water, the object is positively buoyant and will go up. When an object weighs 2 kg, but pushes aside 1 kg of water, the object is negatively buoyant and will sink. When an object weighs 2 kg and pushes aside 2 kg of water the object is neutrally buoyant and will float at exactly the same depth it is at. Just like a diver would. For a ship that means it will have a certain draft where the ship weighs as much as the amount of water it displaces. If the ship then loads more weight, it will go a little deeper in the water, and if it unloads, it will rise a bit more out of the water. The buoyant upward force and the downward gravity force are equal. This video is more about stability though. That point of gravity from the ship and buoyancy from the water create a torque/moment between each other. If the weight on the ship stays the same, the point of gravity stays the same, but the point of buoyancy will change when the ship rolls because the distribution of the volume of water changes. Torque=force*arm. Force stays the same, and when the ship heels the (horizontal) arm increases, until the torque between downward force(gravity) and upward force (buoyancy) is the same as the torque of the disturbing element (wind or wave).

Ps. It is a nice video. Doesn't cover metacentric height, but still, really nicely done.

Thanks M Tieleman. I did intentionally leave out metacentric height as it was a little too detailed for this video. I will try and cover it in another video though.

Ernest Jay A factor that is at least as important as the weight of the water itself, is the effect of free liquid surface. Any slight tilt a ship experiences allows the water in the pool to move in the direction the ship is tilting, which shifts the center of gravity of the ship in the same direction- intensifying the tilt, effectively a dangerous positive feedback loop. This is the reason pretty much all swimming pools on ships are much longer than they are wide, as a greater width greatly increases the aforementioned effect.

Wait... the pool doesn't 'add' to the center of gravity; the center of gravity is a single point. A pool higher up on a ship will RAISE the center of gravity, which I would guess the designers have to be extremely careful about. The idea in the video is that the floating ship will tend to be more stable the lower the center of gravity is.

@@BearLamb123 yes, like water on the car deck of a ferry. M/S Estonia back in 1994.

Good point , but it doesnt 'add' to the centre of gravity/bouyancy . The simple fact is that the pool is in the middle due to obvious reasons yes but the centre of gravity was there and the pool may tip it out if sync

Thanks for the comments Rob!

Ok

Thanks monkeycarz. I'll add that to my video ideas and look to do a whole video with a few examples.

Very very good.Been living on a boat for 14 years.I have learnt something-at last!

Thanks Jonathon, glad it helped.

There was that terrible movie "The Poseidon Adventure" where the ship turned turtle and the liner that turned turtle in Hong Kong harbour.

The arcs of the CG vs the CB are what controls how far over the ship can roll and still self-right All you have to do to make a ship roll on over is to exceed the maximum self righting list angle AT ALL and the ship is doomed if you don't have some other force acting to bring it upright. Every ship design has an unladen maximum "list" before capsizing and that is easy to plot, because you know where everything is on the unladen (no passengers, cargo or fuel) CG of the ship will be. Add cargo, fuel , consumables (food stores, etc) and the passengers, luggage and cargo and calculating the max list angle can be obscenely complex (especially when all the passengers decide to go the to port rail to watch whales at the same time) To deal with moving cargo (people) and to make the ride smoother (less vomiting by the moving cargo) modern cruse ships use gyro stabilizers. That works as long as the gyros are big enough and they have power. With CG well above CB, it doesn't take a lot of list angle to go past the point where the ship can't self-right. Some ships can't survive 10 degrees without the gyros. (this is stupid)

Thanks camdentrain. Glad you enjoyed it!

Thanks Dan. Glad you liked it.

Thanks for the kind remarks Andy!

Thanks Acrobatic Cripple

Thanks for the comment Widget

Thanks Jim. I appreciate your kind words, and am pleased that you liked the content.

Thanks jefftube58

Thanks Pinhead Larry. Glad you enjoyed the content

Thanks Jan. More are coming each week. I enjoy the physics too, so more like that will definitely be coming.

Thanks Arnold. Glad you found it useful

Thanks for the comments Ross!

I rarely comment on youtube videos but was glad to do in this instance. Thank you for the thanks.

keegan773. Wow racist lately

Kyle Wickett I might be "Plumpist" can't see how that relates to "Racist".

Myles Lee Did you have to move cabins?

Lol

keegan773 ... Just goes to prove how stupid race baiters can be.

Thanks FSEVENMAN, glad you enjoyed it.

Thanks madee. Glad you found it interesting

The difference is arbitrary and the forces in use are the same.

Glad I could help!

Overwatch😎

The Reaper and then you remeber that humanity is the single most violent species ever to walk the earth. Just beacuse everyone is scared of going to jail, and therefor behaves, does not mean we stopped being humans. Yeah humans suck hard, if they are not kept under complete controll, they just start raping and killing eachother for funn. Refrences: human history..

Babies are born not knowing bad things ryt?. Humans came violent or bad/evil because or depends on their environment.

The Reaper oh dear lord, someone has not been. Good boi in school, i wonder what factors during your childhood made you unable to understand words. But really tho, how many times were you kicked in the head l

Most are dumb as hell and useless though.

Thanks Jamie. I appreciate the remarks.

Please define Gelo, unless that was a typo. My spell check corrected it as help, and helps makes sense.

Thanks Keith

Thank you for the comments Peter! Glad it answered your questions.

"Dollae"

Your brain isn't exactly wrong, the tilt/roll window in which a ship wants to return to 0° (vertical) is much smaller than the tilt window where the ship wants to lay down on its side or even fully capsize. Fortunately ships usually have a surprising generous range in which they can roll without loss of stability. (And some coastguard boats can actually make a full revolution and be fine, but the passengers may want to wear a seatbelt for that)

Thanks Jah Roos!

Thanks Paul. Glad it helped.

Theoretically yes. But in reality the weight of stores and fuel is replaced with ballast water so the ship remains stable.

In warships they can consume their stores and fuel and replace the lost mass with water ballast. Failure to do this has lead to ships being lost when they encounter storm conditions in a light ship condition.

hyper X, thanks for the comments. Stabilizers are fitted to most passenger ships, but all they do is dampen the roll to make it more comfortable. They aren't actually needed to prevent a capsize.

Yes, stabilizers do not change the CofG or buoyancy, they work hydrodynamically to counter roll for the purposes of making the motion more comfortable for passengers.

I recently took a cruise and was disappointed by how effective the stabilizers were. I was hoping to feel the roll of the ocean more. It was more like being in a tall building in a breeze, unfortunately.

hyper X i agree and i have seen 3 cruise ships go over and stay on their side. I've seen far to many people die from Cpts trusting exactly what you mentioned just to have them fail. It's super rare of course. Yet, it does happen and typically from MASSIVE waves. Especially, rougue waves! Some of these Captains believe they are so unsinkable they will tell you a hurricane is just really ruff water. Storms can create waves way ovet 100' w/ a much larger trough. In huge storms these can easily knock over these ships as the equipment to warn of a rogue, etc... Can appear to quickly or be camouflaged by breaking waves and rain/hail keeping crew blind at the worst moments. Worst for me was hearing a specific one go under before we could get close. None of us thought we were coming back yet we made our peace and tried till we realized what was happening from what lil we could make out till radio silence. Later it was stated how the Capt knew his ship did not have the proper integrity for that level of Hurricane. He got blamed for all of it. Yet when we checked charts, timing , etc..: he actually took best course available. Screw those thinking they r unsinkable in this way. It just takes mother nature to decide y'all r not needed to her. I really hate people thinking humans have mastered mother nature. She will forever win.

Nor are they used to prevent capsize. Only correct stability can prevent that. Horizontal rudders only counter roll.

Yes if the bottom was more like a semi circle (much like a yacht) then it would have zero self righting.

@@stevecurtis1088 Well it would be stable if the center of buoyancy was above the center of gravity. The weighted keel of a sailing vessel insures that is the case. As I understand it, there is a "sweet spot" in a normal hull of how much difference there should be between the CB and CG (the meta-center height) so that the vessel will have a stable oscillation or roll when in normal sea conditions and have good roll recovery in heavy seas and wind. If the meta-center is too great it becomes too much of a good thing. Instead of rolling the ship would tend to be pushed over pivoting more about the keel than the center of gravity into the lee side water making recovery sluggish. Cruise ships seem a lot like a barge in having a negative meta-center height thus depending on wide beam and shallow draft to provide stability.

@@aceroadholder2185 That makes sense. Yes I suppose it's like any sort of oscillating/damping challenge where you can optimise for stability against a given level of agitation. Ie you can make a boat more stable/smooth in calm conditions but it will be unstable in rough conditions. Or you can make a boat more stable in rough conditions but it'll give a harsh ride in more gentle conditions.

It was in my syllabus for GCSE science. GCSE's are taken in secondary school in the UK.

@@jamesmccann5644 Was it in the old syllabus?

AFAIK buoyancy usually is (Archimedes principle), but stability isn't.

@@SuccessforLifester yeah, did it about 5 years ago now.

@@BooBaddyBig not directly, but the different forces causing buoyancy, and moments are. So all the components are. There was just no section saying that moments happen with buoyancy as well.

More like the centroid, than the center of gravity. Centroid is a geometrical term that doesn't care about kilograms or gravity, rather than a physical term that does. It is the center of gravity of the region, if it were filled with a uniform density material.

Thanks for the comment. You are right. The correct term is "capsize". In my more recent videos, there is a lot more terminology. This video is very much only a basic introduction to some concepts.

Well in this case you are talking about listing. Capsizing is the end result of too much listing.

Harvey Millar. You are correct, ships capsize, but boats, crewed by lubbers, tip over all the time. Pretty good explanation of center of buoyancy?

Really, most reports of ships capsizing say it capsized or over turned , not tip over

Jesus people get over yourselves. No one cares how much you know about ship terminology

Thanks Niall

Thanks Elr. Glad you found the video educational.

The sea isn't for everyone OneKindWord.

Thanks Jack. I am pleased you liked the delivery. There are so many technical sources, I wanted to communicate the fundamentals in a way everyone can understand.

Yes. That is how many sailboats are designed. Most of the weight is in the keel, and if the boat capsizes the COG will be above the COB and the boat will right itself again...

You are 100% correct. This does all only apply if the hull is intact. As soon as there is a breach, the stability situation changes completely.

The Casual Navigator i think when engineers design a ship they should go back in time and study how so many passenger liners have sank in the past! Too many liners have been lost! The ocean floor is littered with them!

Not all sinkings caused design but many by human error.

Oops 'by design'

Harvey Millar human error usually initiates the sinking process without a doubt but the physical process of the ship sinking often exposes design flaws or shortcommings! Imagine if the titanic was a double hulled ship with true water tight compartments!

Thanks Katie. Glad you found it interesting!

If it hits the side with enough force/energy to overcome the ship's righting force/energy, then yes, the ship will capsize. It is more likely is that a wave that size would break the superstructure and flood the vessel before capsizing it though.

Poseidon (2006)

Thanks Plasmastar 23. Poseidon is only fiction though

There was a cruise liner that did get hit by a wave and rolled to the point of inability to self-right. It laid over on its side for a long time before going keel-up.

The point of no return. There are charts of this for every ship for each condition, heavy, regular, light and drydock loads. Not sure of the terminology but if a heel of x degrees is exceeded on any vessel it will stay over or capsize.

they're*

Alex Moss lol

You corrected "There" to "They're", but not "to" to "too"? I'm shocked.

you can't hand everything to others on a silver platter.

jasexavier to dose not matter to me

Thanks partybiscuit

Stuart Lee the fuck is it then

@@ThornyA_D39 An ocean liner.

QM2 was built as a liner, but is used as a cruise ship. She does still serve as a liner for a bit each summer, but she is mainly used as a cruise ship nowadays.

She is a dual purpose Ocean Liner/Cruise Ship as was QE2. She is doing more Transatlantic crossings than ever these days (into November for example).

ships are ships having all principle of keeping them upright

liners go into the bin don't they?

They're all big honkin' floaty tubs to me.

Thanks for the comment Dan. As you say, I have kept this video generic, only explaining the broad details. I may expand on it in the future, though the topic is so large it would take a very long video to cover it all.

Thanks for the tip Mr Documentary. I was considering a run of shorter videos to gauge interest, but I will still also continue the longer ones as those are the ones I enjoy making.

i mean you can make longer videos, its not that, its just this particular subject is not going to keep someone watching 5 mins

something seems off with the audio recording also, not sure if getting a better mic would fix it. The audio just doesnt seem polished I guess is the best way to explain it.

Also, put a little more time into the graphics. It will help add retention and subscribers by giving it all a more polished look.

Cheers. I only started making videos in December, and this was one of the early ones. Very much learning as I go. I only used kit that I already had as well, so the mic was just from my ps4 headset. I have replaced that now, so hopefully there will be improvements on newer videos. As for graphics, I only use open source (free) applications, and am learning those as I go too. Again, hopefully there will be improvements in time, just through practise and any investment as I can afford it. Thanks for the tips though!

it hit rock bottom, literally, all the physics in the video, mean nothing of you have holes below the water line

It hit a rock and water entered the ship from the bottom, adding more weight to the ship, causing a capsize.

Water came flowing in, changing the wight of the ship.

Live On. It almost tipped over. Had it been captained by a salt it never would have come to grief. It was captained by a boy clown so it tipped a bit.

Concordia ripped a hole IN ONE SIDE and flooded compartments on that side. It drastically moved the CG to that side AND removed buoyancy from that side moving the CB (Center of Buoyancy) to the other side. Slide the Green dot a LOT left and the blue dot a LOT to the right and as the ship rolls it just makes it want to roll more, rather than self-correct. The gyro stabilizers can deal with this on a relatively small scale (similar to all the passengers going to the left side of the ship at the same time to watch whales), but they don't work when you put water in their compartment shorting them out and adding the water friction acting on the gyro discs. They stop pretty fast when that happens. Before the water could move to the undamaged side of the ship through open hatches, the ship had rolled beyond its maximum list for self righting even with the gyros working and it flopped on over until the superstructure (everything permanently bolted to the ship above the hull) hit the dirt rocks and coral. Just not enough positive stability built in to deal with a hole that the ship could have survived if it didn't roll and not enough pumping capability to force water into "trim tanks" fast enough to counter the roll. And the ship "turned turtle" (the part of a capsized hull sticking up out of the water, of a 1800's sailing ship, resembles a turtle shell) ******************* USS Enterprise hit an underwater mountain and DAMN NEAR capsized. They expected it to go down due to the ship exceeding max unladen list angle by several degrees. Fuel, weapons storage and supplies being stored low + high capacity trim pumps + using fire hoses to purposefully flood compartments kept it upright (and a lot lower in the water moving CB up)

Yep

Thanks 1oldmariner. That was the aim, so I am glad it came across that way

Thanks Intervallum