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In this video, we investigate why fatter ships appear to "wobble" while thinner ships tend to go in a straight line. It's a concept known as Directional Stability and is really interesting once you start looking into it.
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2 weeks ago, first by a mile
Another informative video Casual Navigation! Thank you for partnering in making our mission more accessible. For those who want to be better informed and compare media coverage, check out the link in the description.
Didn't expect to see an ad from Ground News. I really like what they're doing
Seriously? An ad in the MIDDLE of a six minute video. Ground News is going on my list o' feces.
Don't forget prismatic coefficient. It is the 3d equivalent of the block coefficient.
i didnt come to Casual Navigation to feel personally attacked lmfao
I hate it when i get called a fat ship with no directional stability :(
Being reminded that you’re obese is not a personal attack.
@@miro007ist he's joking.
@@miro007ist Wow. You must be fun at parties.
Getting insulted within the first minute. Brutal. 😅
I'm a huge fan of your videos and how informative they normally are. This one, however, is the first one that leaves me with an unanswered question. Why do fat ships wobble? Because their LB ratio is low...? That's kinda just saying a fat ship is a ship with a low LB ratio, which is pretty obvious. But how does a low LB ratio make a ship less stable? Something to do with water pressure on sides of the hull? An explanation as complete as in your ship speed and efficiency video would be quite welcome!
Yeah, I was surprised he didn't go into more detail
I essentially think of this as wheelbase with cars. A shorter wheelbase means the car is more nimble, but equally more twitchy, e.g. doesn't go straight at high speeds as well as a longer wheelbase car. Now since ships don't have wheels you can't really say wheelbase, but you can have the ratio of the length:width and voilá (you could just have the same thing with cars and it would work the same). This still might not/doesn't answer your question, but it might just be more intuitive, at least it is for me. Edit: wider cars can be more stable as well, so it's not the same as LB but is similar enough for me to consider it is an analogy.
He would have to get into how the center of lateral pressure moves around and how far ahead of the center of mass it is in each ship, and what the C of (L) P is, which would probably double the length of the video.
@@jirivorobel942 but overly detailed explanations of maritime concepts I don't really use is exactly what I come here for. This was more: are shorter ships easier to turn? Rather than: why fat ships wobble
Yeah this video was considerably lacking unlike his usual videos. Not great when about 20% of the video is an ad.
I always appreciate that you include the occasional nod to the great lakes ships. I would love to see something on our thousand footers. And the old whalebacks are my favorite.
Edward Aurand 👍😁 Love the Roger Blough and Presque Isle!
I grew up near the Seaway and its truly a marvel of engineering that doesn't get enough appreciation. As a kid i knew it was used for trade but i never realized that the Lakes and Seaway enable inland cities like Toronto, Chicago, and Deluth to be ocean teir port cities with none of the downsides of being on the ocean. (Military/strategic, climate change, normal storms, or even just dealing with the tides) Its also crazy how you can literally go to the locks and spend all day watching the ships for free and nobody says anything.
@@jasonreed7522 The big downside was all the invasive species that have been introduced to the Great Lakes. Very detrimental.
@@terryboyer1342 invasives are definitely a problem with global shipping, and as great as a 2GW hydropower dam is for emissions, its also really bad for the fish. Another thing thats bad for the ecology is how we connected the Mississippi to lake Michigan via Chicago. While it lets us sail all the way around the east coast without going around the west coast (kinda meme thing to do), it also means any invasives in the Mississippi can get into the Lakes. (I believe asian carp and possibly a lamprey species are the big concerns right now that we want to contain to the the smaller Mississippi) PS: the Mississippi carries less water by 6m^/sec difference in average annual discharge. (Bigger drainage area, less water, not sure if human consumption is accounted for in the number)
I recreated one of those whalebacks in the game stromworks once. Very interesting designs, those ones!
Its the same thing with old tanks, the length to width ratio determines how hard it is to turn and also how sensitive it is to do smal corrections while driving in a straight line.
That’s why battlecruisers (a lighter but faster battleship) we’re typically longer than their battleship counterparts yet still lighter, bc they were a lot longer but thinner, therefore making them able to achieve greater speeds but it did cost in agility as trying to turn a long plank of metal half submerged can be kinda hard
For a cruise ship, having a larger length-beam ratio also helps to have a greater ratio of passenger cabins with windows.
Great video! This is similar to aviation in that dihedral wings (curving upward) like you find on airlines require more effort to turn, whereas andihedral wings (curving downward) like found on large military aircraft want to turn, thus being more maneuverable.
You can experience this effect really well in a kayak. Those long skinny kayaks are really easy to cruise with and keep straight. The more stout and wide kayaks, while better in rough waters because of their lateral stability, they are constantly moving left and right as you paddle along. And if you try to go really fast in a stout and wide kayak it has a tendency to turn so much that you lose control and spin out, which can cause you to capsize.
is that why I can't walk in a straight line?!? love the content! always love the detail, keep it up!
I've been on a ship once in my life. I'm 44 now. In all likelihood I'll not be on one again in my lifetime yet, here I am watching your videos.
I feel like I missed the reason why "fat" ships wobble. I know he mentioned how the different shapes of ships act differently, but I don't recall hearing why a fat ship wobbles and why a skinny ship doesn't.
directional stability, the bigger ship needs more rudder input to keep it straight which could look like the ships wobbling.
@@TitanicTours27 yes but, why? We just heard that the fatter hull has less directional stability, so we know it'll need more rudder input, but why?
@@patricknorton5788 An analogy is how a figure skater will spin much faster when they bring their arms close to their body, and slower when their arms are straight. It is not the same mechanism, but the effect is the same. A longer boat has more water to push sideways to turn, further from the center. This takes more effort.
@Eric14492 that makes some sense (and I have experienced the difference and trade-off between maneuverability and efficiency/tracking ability in using short and nimble/or long and fast kayaks and cross-country skis). The point was, though, that the video didn't explain it, even if you can.
fluid dynamics 🤷 something to do with how higher length-beam ratio ships act as a longer lever, so the water on the sides has more impact on the motion of the boat than the water at the front and back? I dunno
Great Lakers, and I loved how you used the Edmund Fitzgerald by the looks of it
I cannot unsee the surprised face, with a pink hairdo, on the bow of the Great Laker at 4:20
Maybe I missed something, but this didn’t seem to answer the question of why they wobble. Why do they continue to “steer” even after the rudder has been recentered?
Maybe they are essentially aquaplaning? A knife will cut through water and find a direction to go in, whereas a baseball bat will go whichever way its momentum takes it.
Great video as always. In the future could you include explanations for why things like "fat ship wobble" and "chunky ship wobble" occur? Those are always what I found most fascinating in your videos.
Now I'm imagining a tuba player on a tug boat playing background music for a wobbly fat ship.
okay but why does this happen
I've felt the same thing on a kayak. It just didn't want to go straight, just paddling one stroke each side alternately wouldn't keep it straight, you constantly had to give more strokes on whichever side it was trying to turn towards - and be ready to swap to the other side the moment it began to swing the other way. I think it's because the streamline flow at the rear prefers to flow diagonally one way or the other. I've also heard that certain airliners do the same, they tend to crab slightly, albeit they have a whacking great tail fin to restrain the tendency.
Having grown up on Superior, seeing Lakers used was fun. But the block coefficient and L-to-B make an interesting set of parameters to design around.
There are even larger ships on the Great Lakes that are designed to the limits of the Soo Locks. But those can't operate out of the lakes because they can't make it out.
Having the QM2 in a vid of yours always makes my day! I loved working on that ship :)
So I've been to an island wedding on the St Lawrence. The rumor was that the lock operators would time it to where a cargo vessel would pass by during the wedding.
great video during my time in subscripted military service I spent a lot of time on the wheel (vessel was 50 metres long) it was mostly thinking 5 seconds ahead to keep it on course :D
I'm not chunky, I'm just big beamed.
I found this when rowing. A long boat is easier to control than one that is shorter and wider. There was no rudder on either of them. Granted, the longer boat had a deeper keel, and cut through the water beautifully.
I think this video could use a follow up diving into why exactly the fat ship wobble happens. I wonder the physics are similar to the overbanking tendencies or adverse yaw found in Aviation?
Excellent video, as usual. Nice to see the block coefficient explained. You don't come accross this term very often, but I used it a lot when I was designing fender systems in a previous live.
I never would of imagined there was so engineering involved in building and operating ships!!!! Thank You!!!
fantastic vid. where i work we have 2 boats, one is 55x12 ft the other is 57x6'10" most people have definitely found our narrowboat to be the easier to drive of the 2. they've put it down to the narrowboat being on a tiller while the widebeam being on a wheel, but i reckon the fat ship wobble plays a part too
I kind of wish before showing a rudder corrected course you showed us a simulation of a ship with a length to beam ratio of 3 making a turn and then keeping the rudder in the center to let us see the constantly changing direction.
This explains so much about my skiff, my new one is wider than my old one and it just won’t hold straight
Sea kayak vs recreational kayak makes this very noticeable. The tracking stability of a sea kayak is very noticeable compared to a recreational boat, which often turns direction every time the paddle is applied to the water. Even more extreme a white water kayak is short and stubby to make turning as easy as possible.
Yes I noticed this the one time I used a kayak (in a calm lagoon). Very frustrating, the bloody thing just didn't want to go in a straight line at all.
Your narration and (importantly) the choice and volume of the background soundtrack is pretty damned good. 👍👍👍
As someone who lives on Lake Superior, it’s always nice seeing some Laker appreciation
I've never steered a large container ship. Thanks for the explanations. I always see them under fine control when attended to by tugs. I'll have to watch them in the Bay and see if I can detect the wobble when they are not in tow.
I always learn something new with your videos man!
Huh this is interesting. Aeroplanes have similar performance characteristics so it’s interesting to know how attitude stabilities affect ships as well. In aviation, we say that planes that keep increasing in the relevant attitude axis once control input returns to neutral have negative stability on that axis, 0 if it maintains its attitude, and positive stability if it returns itself towards the flight trajectory. Negative stability is primarily used in fighters.
I love your channel as an Engineering Cadet!
This is amazing, these same concepts are fully in play in the world of motorsports as well
This is super evident on leisure crafts such as Day Cruisers that wobble like there’s no tomorrow having an LB of 3 or so.
Very interesting. Thanks for sharing this with us.
Fascinating! I'd never heard of such a thing.
A simple explanation as to why that happens. You have centre of mass of the vessel and centre of propulsion as well as a centre of resistance which are all in a straight line when the ship is moving forwards. Ships are rear steer objects so the centre of thrust moves out of line which then presents a bit of the beam to the forward flow of water across the hull effectively moving the centre of resistance across in the opposite direction so the vessel will continue turning about a centre of rotation usually near the centre of mass. This happens every time there is a rudder input. This happens more for wider vessels as a certain angle of turn causes a greater movement in the centre of resistance. Long thin ships tend to get stuck with nice flows along both sides of the vessel which are hard to break so difficult to imitate turns. Both of these problems are solved by proper rudder design and a ship which is excessively prone to either of these conditions could be rejected by the customer at the sea trials stage. The ship with a high block coefficient has the wobble problem as it is effectively a brick in water and the forces acting are higher for a comparable vessel of same length&beam. As a naval architect you can spend months conducting operability and control assessments on a design in CFD and other simulation softwares before designing your rudder.
As an aerospace engineer, I suggest to increase the yaw stability volume. Maybe itroduce a deployable vertical stabilizer on the long distance legs in order to reduce fuel consumption and crew workload.
Fascinating. Thanks for sharing.
this just made me remember that the popovs existed. late 19th century russian warships with a length to beam ratio of quite literally 1.
Dude you’re more reliable than google when it comes maritime info
Love the videos
Very informative content⚓
My boating experience is very limited yet my enjoyment of these videos is very high!
You might as well start exploring spaceship movement. You explain the concepts so well.
While you are right about the Great Lakes Lakeboat bulk carriers that can go through the Saint Lawerence seaway, there are a number of "footers", which ar 1000+ feet long and hence "lake bound". Just adding detail to your story, not trying to argue.
"I like low length-to-beam ratios and I cannot lie, you other skippers can't deny"
Ok but why do Length to Beam Ratio and Block Coefficient impact Directional Stability? What’s the mechanism here? I feel like you didn’t answer the question in the title tbh
Video title : "Why Do Fat Ships Wobble?" Answer in video : "Fat ships wobble." XD
@@TarenGarond Actually, the "answer" in the video is that fat ships wobble because they're fat, since "low length-to-beam ratio" just means "relatively wide for its length", i.e., "fat".
I found this episode very interesting. I had no clue that this is a thing. Now I know. Even though I still don't get most of the math
This is precisely why ikea carts are so difficult to handle
That's a great sponsor!
This may well be true. We all want that long fat ship though.
I see the Great Lakers all the time. I live right on the Welland Canal
I did not quite understand your explanation of the block coefficient, could you perhaps review that again in a future video?
Most "Lakers" don't traverse the St. Lawrence locks as that would make them "Salties". But they do traverse the Wellad Canal and the "Soo" locks so the constraint still applies.
6:05 "ships with a lower length-to-beam ratio... are generally faster and more efficient" I'm confused, I thought we just learned that higher length-to-beam ratio was more efficient due to not needing to use the rudder as much when traveling straight
Yeah, I think he mis-spoke there. Should be _higher_ LB and lower block-coefficient.
Hey, love your videos as do my kids. This made me think of the Norwegian navel and seismic survey vessels the Ramform design. Flat bottomed and 150m long and ~70wide for the latest Titan class. The previous classes were narrower and were supposed to be stable but rolled massively in the slightest long period swell, the tank tests they did for designing clearly missed something... fun but not that fun to work on for weeks at a time. If you ever wanted to do an episode on them I worked on them for years so happy to answer questions. The Banff was a ship oil storage facility built before the seismic vessels that cost millions to fix due to not being stable, and same mistake went on with the first seismic vessels, could be an interesting story to cover all of them.
Thanks for the explanation! I have a science background and the ship dynamics you described are clear to me as I took mechanical physics course. I’m thinking that describing the ship itself as a rudder and how the efficiency of that effect is affected by certain variables may be a good metaphor to explain. What do you think?
But there wasn't any explanation! All he said was that fat ships wobble because they have a low length-to-beam ratio. But "fat" just means "relatively wide compared to its length" or, in other words "has a low length-to-beam ratio". So, in ordinary English, the video just says that fat ships wobble because they're fat.
So glad to actually understand the real life scenarios of the things I just discussed in scho
Never thought a video on ships can be useful for scale modelling
Water an air work in very similar ways, i think a good way to illustrate this is to imagine a ship like a dart or ball Ships that have a larger LB ratio are more like darts, the center of mass of the vessel has a large surface behind it to create drag and self stabilize the ship. Just like when you throw a dart, the fins keep the dart straight along the arc it's travelling on even when the direction it's pointed is disturbed On the other hand Ship's with lower LB ratios are more like balls, there's less of a surface behind the center of mass to act as flukes, and when you throw a base ball or basketball it very easily spins in the air, and In the case of a baseball this spin can very easily change the direction of the ball (though that's a different effect entirely)
I live so far inland and have no personal or professional need to know about shipping. WHY AM I OBESSESSED WITH THIS CHANNEL?!?!??!
Lesson of the day: Titanic would've miss the iceberg if it is chonky
Very interesting to say the least but it all comes down to what the ships purpose is and whether you're trying to maximize one thing or another.
How do you make your videos ? Which software do you use ? I have a college project so asking for the same reason.
Ok but why? You just gave it a name. It is quite analogous to transverse stability. The hidrodinamic force created in a turn lies far fwd for a fat beam and have a bigger arm increasing this turn. It is the same as if the ship was trimmed by the head
I wonder how this applies to catamarans. My buddy has a 55ft catamaran that has a beam of 29ft. Each hull is stream lined and only gets to about 7ft wide. We were having trouble keeping her in a straight line and were going to see if there was slack in the steering. Wonder if it's just the boat dimensions.
I imagine that in a certain way, there is the angular momentum. When turning a ship must also add angular momentum to its own referential.
"This is 9/10, but..." Nice one.
There are many optimal ratios that go into engineering a vessel that runs stable and efficient. Beam to length ratio is probably the most basic of all.
There’s a similar phenomenon with smaller vessels such as dragon boats. The 20-man version has a ratio of roughly 10.5:1 and is relatively simple to keep straight and inversely difficult to turn, however, the 10-man boat has a ratio of probably less than 7:1 and is a pig to keep in a straight line and likes nothing better than to zigzag down the course, given the slightest provocation. Ask me how I know.
So, how do you know that?
I'll have to watch them next time I'm out sailing as I see them in the estuary training. They do also have boxy, ungainly looking hulls. I don't know if adding any lateral surfaces like a keel or just aft a skeg would help. It would add drag and wetted surface. Looks fun. I should try paddling a dragon boat someday.
@@alwaysbearded1 I’d recommend it. It’s a great way to get fit and meet people and in the 8 years I was involved in the sport it took me all over the world for social and international race events. What part of the world are you from?
@@thechumpsbeendumped.7797 Got too many irons in the fire as they say now. Got the boat I sail on, the house, car.... busy life. Maybe when I retire in a few years.
I'd love more Great Lakers information from this channel. I noticed that the model of thr Laker looks like the Edmund Fitzgerald
It could very well be a reference but also the Edmund Fitzgerald is still considered a pretty modern ship by Laker standards, she was not terribly old when she sank so they haven't actually made too many more since then, if she was still afloat she'd probably still look pretty current.
Seawise Giant casually steaming with a tuba playing in the background.
Sounds like an extra factor that was at play for the Evergreen, outside of the positioning on the canal?
Why ignore the third main factor (arguably the first), the keel? I live in Tübingen where we have the "Stocherkahn", an unique riverboat pushed by long wooden rods. It is completely flat on the bottom and thus drifts a lot (which can be exacerbated by wind or a strong flow)
Your "unique" boat sounds exactly like the punts that you can hire in Oxford or Cambridge.
I was about to say... sounds like a right punt!
@@iankynaston-richards883 and a frigate sounds like a destroyer. There both ships with a motor.
With a design like a WW2 battleship I wonder what effect prevails. Bismarck for example has a length to beam ratio of 6,71 but a low block coefficient with its double ogive hull shape.
Ok but why does the length to beam ratio and block coefficient affect directional stability?
Tugboats are just the most adorable things from a top view lmao
Where can I get that Ship turning simulator in the start of the video?
As I understand it, there is similar stuff with Airplanes. The average Airliner wants to stay right level, flying straight. Which makes them harder to turn, but more more fuel efficient in cruise. While combat aircraft are designed less stable - to actively unstable like the Eurofighter - as that increases maneuverability.
How does this translate to yachts? Many modern sailing yachts have a shape that looks like a clothing iron from above, and quite flat bottom-Hull. Or does the keel counteract this a lot?
on small leisure sport cruisers (8-12m) at non planing speeds you also need to steer a lot. is that the same reason? those are normally having len/beam ration about 3:1... those are normally at water line rather pointy (low block ration). do those principles translate to those small boats?
The hull shapes also don't always have much of a keel. But as you said, at planning speeds the contact with the water changes completely to a very small length. Not sure what the contact patch looks like in beam but they seem to be whatever the beam aft is. But whatever you do, don't go slow next to small boats and sail boats then gun it the second you are past. You create the biggest wake or hole in the water at that transition time. Wait until you are well past and clear.
It is observed easily in the ship simulator as well especially during mooring.
It strikes me that the ship with the lowest possible block coefficient would be a four pointed star, which would probably have terrible directional stability even with a high length to beam ratio lol
How does this work for catamarans? A 20m long catamaran with a beam of 10m and 2, 2m wide hulls - is the length to beam ratio 2, 5, or 10? Does it wobble?
It's kind of like a bicycle vs a tricycle at high speed. You'd think the tricycle would be more stable but at speed the bicycle has it beat
I just wanted to tell you that the thumbnail of this video combined with a couple of others in my recommended more or less just said “too fat? HORRIBLE FATES. Too Late!” With an ad for sonic corn dogs right above it. It certainly made me laugh.
It also had a thumbnail right below it with a speech bubble that said something along the lines of “come on do something”
Ahhh, fat shiP....I was so confused. Definitely want merch for this :) Love this channel!
Alot of this seems to also be assosiated with trailers. A smaller trailer might be 12ft long and 6 ft wide. They turn insanely fast but hate going straight, your often seasawing the wheel to get it to go straight back. However a 30ft trailer that's 8 ft wide will be tough to get started turning but keeping it straight is much easier. I don't know if they're related but it seems they are. I have an additional question as well though. Does a single screw ship of the exact same build with this fat wobble turn easier then a ship with two screws assuming everything else remained the same, including thrust, rudder size, etc?
When zoomers become naval engineers: "how the hell does your ship turn so fast!?" "L+B ratio scrub"
Is that why the Iowa-class have those enormous snouts so they can be really thick and chunky to fit those massive gun turrets on but still maintain a low block coefficient and improve directional stability at their cruising speeds?
So it IS about size and shape over "the motion of the ocean"! I've been lied to!
How does a twin Hull catamaran experience the ratio and coefficient?