....plus you would have understood how critical it is for large ships to be able to get up on plane if they're going to be any good, especially with efficiency plus speed together. If 590-ton craft can leave the ground supported by nothing more than a gas, what's the hold up? How can we expect planing not to be standard on large vessels? 😊
@@ReflectedMiles sounds like you are suggesting hydrofoils. They are not efficient for larger ships. Please note my Naval Architectural degree is focused on plastic bathtub toys.
As a docking tug captain, this is cool to see in exactly the opposite way 😂 Practical demonstration is all we get. Learning pressure zones on different hull forms is a very stressful experience.
@@krombopulosmichael6162 No in the video plane speed was beyond the hump speed where the wave peak is at the bow and the trough at the stern, so the engines push uphill in addition to water resistance.
@@RobBCactive most ships are not designed for plane speed though, according to the video. It does mention bulbous bows, which are becoming more common.
Thanks for the explanation. I've often wondered the same. Years ago, I was on a 42' private vessel crossing the Panama Canal. The Canal obviously has too much traffic to let a puny motoryacht take up an entire lock, so the Harbormaster put us in with a cargo vessel -- large, but sufficiently short to accomodate us both -- for each leg of the trip. On the way up, the big ship entered first, and we behind her. When we reached the lake elevation and that ship fired up her engines, her prop wash was so intense that the only thing keeping us from getting bashed into the sides of the lock were the six lines the Canal staff gave us (delivered by the famous "monkey fist") that held us tightly in the center. Still, all open beverages were immediately spilled. When she got underway and we followed, I was amazed at how quickly she put distance between the two vessels. In no time at all, we lost sight of her. Of course she made it across Gatun Lake in a fraction of the time it took us. The Canal staff knew this would happen, so they had previously scheduled us for a departure with a different vessel. This time, her length wasn't an issue, as they put us in ahead of her, and her bow literally covered the space we occupied. You don't truly get a sense of the scale of these beasts until you have looked straight up from the deck of your boat and seen nothing but metal above your head.
Now try living on the water and never taking a job or learn how to drive big boats and ships and watch these videos. I'm In my 30's and love these videos I wanna change my career. cheers
wow, I think this is the first time in my life, where someone used the term "wave length" and is actually talking about waves. (I am an audio engineer with a fable for physics, and I know, that those other waves are waves, too... but you know what I mean) And also, that was an utterly interesting video, thanks, I learned a lot^^
I spent 23 years on aircraft carriers. Being retired, I now work around a lot of Airforce dudes. None of them believe me when I tell them carriers are the fastest ships in the fleet.
I was thinking it was due to a ship 2* as long, wide, and tall having 4* the surface area (for drag), yet having an engine 8* as powerful. Didn't think about the wave interference. Good video
You could easily expand this video with the hull shape aspect alone, ldl hulls are faster and lower fuel costs. a good example, an 85' loa motor yacht with a draft of 4 feet designed for displacement cruising. Top speed is 18 knots, cruising speed is 15 knots. 15 knots speed gives her 1,500 nm range on 1000 US gallons of diesel, 18 knots gets you 500 nm from the same quantity of fuel. These same factors are in play with the big cargo ships, yet most people can relate to being told if they slow down by 5 miles an hour they will travel 1000 miles further in their pleasure boat over it's cheaper to ship a 6 week trip than a 1 month trip for your overseas delivery.. *ldl = low displacement length.
@@jaquigreenlees I knew what the acronym was for and was just bugging. I find it funny that we have two measures of distance that have the same unit label :)
it maybe of interest: the bulbous bow works only at a limited range of speeds, because its wave has to interfere as designed with the normal bow-wave. Cargo ship hulls (including the bow-shape) are designed for a resonable range of cruising speed, to be fuel efficient. Intrestingly you can guess a ships speed by looking at its generated wave lenght at the hull. you only need to know how long the ship is, judge the length of the wave and use the formula depicted in the video to calculate the speed of the ship (through the water) ...
Your explantion/guess, does not include water conditions. All vessels: would be much better with a nose bulb ! -- Better for control of spin & steering; -- Keeping hull at a reasonable angle compared to the water surface. -- Better dispersing of the bow's wave. ****** >> A Hydro-plane: -- can achieve higher speeds; -- has less danger of flipping over. ( compares to many automobiles that save gas, with 500lb -- 200 kg of cement inside the rear trunk ! )
Beautifully explained. I’ve heard the waterline length rule touted for years and only recently learned it was due to a longer wavelength of bow and stern waves. You closed the loop for me, easily explaining that the wavelength was itself proportional to speed. Thank you!
Assuming the ship is travelling against and into waves, of course. More often - for speed and efficiency - it'll travel with the waves whenever possible. Sometimes it'll have to travel across the waves, winds and currents don't always end at your planned destination. Sometimes the waters will be calm. Making the hull bulb counterproductive, if anything.
I've seen a boat running at "hump speed" before, a motor yacht. even to my untrained eye, it looked horribly inefficient, like the boat was trying to climb a hill.
@@HelloKittyFanMan. Adding quotes like these usually implies fake, but it can also mean a special or unique phrase. Clearly it's the latter in this case.
No, @@DemPilafian, it was _not_ clear, because if it was then I wouldn't have asked about it. Do you mean like... emphasis? Because if that's what you're trying to say, then you'd be wrong. Because if that is what you're trying to say, then my reply to that is that no, quotation marks are not emphasis marks, or they would be called "emphasis marks" alternately. That's not now, nor was it ever, their job. How anyone would've ever gotten taught that in some presumed "official" way completely baffles me! Emphasis is already handled by *boldness,* _italics
I used to sail small boats as a teenager, and despite not knowing how any of this worked I remember intuitively feeling the phenomenon of hump speed and planing. Especially the boat 'falling' off the top of a wave, going from planing to hump speed, as a gust of wind dies off. Super facinating to learn how this actually works!
Same thing with adjusting the trim on a power boat. At a certain speed and perfect trim, you can just feel the resistance leave and the boat levels out.
also worth mentioning: the drag force is proportional to the cross sectional area of the ship. by the square-cube law, doubling the scale of a vessel will quadruple the drag, but allow 8 times the internal volume for engines to be put in. thus, if your engines take up the same amount of space, you'll have twice the power, and sqrt(2) times the speed
I heard a story about a US navy carrier group deciding to have a drag race for amusement. As expected the smaller ships got the jump at the start, but it was not long before the carrier caught up and passed every other boat…much longer hull length.
Excellent video, I heard the term "Hull speed" but nobody had a good explanation as you put it here as to what happens. Keep up the good videos and knowledge spreading you do!
I did not know the hull speed formula. It's nice to see it confirming my guesstimated speeds for my D&D ship's speed tho (130 ft 3 masted schooner at waterline, assumed her top speed to be around 12 knots. Which is less than hull speed, but considering wind and stuff it's within ballpark!)
Overcoming the hump speed is mechanically the same as breaking the sound barrier. You wffectivly turn a wave into a straight line, saving tons of energy. But it needs tons of energy to overcome the hump/barrier first. And even then it needs more energy then any speed that doesnt approach thr hump/barrier.
There are other ways to defeat the wave effects. Tuning shapes of leading and trailing edges to better suit lamellar flows back into the common plane on the trailing edge is the major factor. Shorter hulls can be made efficient at higher speeds but compromises are often made to achieve other desirable effects. This video however is a good beginner primer for this niche of fluid dynamics.
I thought as much, and thought of the same analogy. "Needs more energy than any speed that doesn't approach the hump barrier." Every time you accelerate from zero, you're approaching the hump barrier. I know you're talking about it as a limit from Calculus, but how close to the hump barrier does it have to be for that factoid to lose veracity? 70%? 40%? Actually, Real Engineering shows a graph of drag vs mach number, and it clearly shows that mach 1 is a peak, and by mach 6, the drag is significantly lower. He was taking about rockets (which are designed to go faster than MACH 1), so I'm not sure if his graph was generally applicable to hurled objects or not. He was discussing the new startup with rockets whose "first stage" is a centrifugal slingshot. I can't remember the video title.
Very interesting, and very clear! In case you were wondering whether a longer, more detailed video on this topic would find its audience, know that you'd have at least one enthusiastic viewer.
I like how you answered the question again but this time with the context of everything we're talking about so the more literal explanation makes more sense. Great way to sum it up at the end of the video.
I had assumed this was just going to be a fairly straightforward square-cube thing, where the drag on the ship scales with the surface area of the ship but the size of the engine it can hold scales more with the volume
Hull shape! When I was in maritime school, this crazy old ex-Navy captain used to tell us, "whatever the question is, the answer's usually hull shape." And it's pretty close to correct, although he didn't like it much when the least-mature adult in the class tried to turn that into a running gag. That ex-captain never could get me to understand hull speed, though, and I never really understood the physics behind planing and the way a small craft's bow rises out of the water at hump speed. Never heard the term "hump speed" before. I've never been able to find this stuff in the American Seaman's Manual, either. But thanks to Casual Navigation, it all makes perfect sense. This is a gem of a video. And then we have the bonus of a big container ship getting up on a plane, and then being fitted with giant jet engines. That made me smile.
Going into this, I thought it would be a matter of larger ships having larger, more powerful engines. That's a really interesting cause, though, and it shows just how much thought goes into every aspect of sailing.
Well, obviously, larger (or underpowered) engines would have an effect. Also, does this rule work as well for pleasure and military ships, where finding the maximally efficient speed is not the most important criterion? The question at the beginning of his video is not well stated, so I'm not sure exactly what I learned.
I was under the impression that the hull speed was the last efficient speed (assuming a slippery hull) before the "wall" of resistance you get as you approach hump speed, due the destructive wave interference outlined in the video. So in the graph it would be found at the bottom of the little dip rather than at the hill before it.
There's a similar phenomenon with the speed of sound. Crossing it causes peak air resistance, but for a plane or rocket that's designed for it, going faster than MACH 1 decreases your air resistance the faster you go. So, for an aircraft, MACH 1 is the least efficient possible speed, compared to any other.
I went fishing a lot growing up with my Dad in our 19ft jet boat, I’d always wondered why the boat pitched and accelerated differently before the boat got on step, and how it would fall off step. this makes perfect sense
Glad to see your method of reducing the condition, for the average person to understand. ********* Beyond the hull waves, there are other factors that apply: -- Water surface conditons; -- Wind conditions; -- Water currents; -- Ship's acceleration/deceration. -- Angle against water of ship's bow, VS the ship's stern. In a smaller vessel: these quickly Add up ! --- The vessel, quickly becomes unstable ! --- Can easily flip over, in any direction ! ( Bow going under the Stern, being least likely, frequently does occur during bad ocean conditions ! ) In a larger vessel: -- These factors, are minor; -- Once up to speed, is very hard to change speeds or direction; -- Being longer & heavier, reduced dangers from waves; -- A skilled captain: can even use ocean waves, to their advantage. ( Using less engine power, to reach higher speeds. )
Informative video. Could you please cover the large, high speed, passenger catamarans invented by Incat in 1990 and developments of that design such as the Austal trimaran you showed at the end of this video? I've always been amazed that craft over 100 metres long can travel at up to 50 knots and still be commercially succesful.
Back around 1890 when they were building the first USS Texas battleship an argument ensued with the designer, the Bureau of Construction, and the actual builder. There were worries that the weight calculations of the ship had been in error and the builder suggested that the ship be made ten feet longer but the keel had already been laid (but could have been modified at extra cost). The builder said that the ship would have the added benefit of being faster as a result. However, the argument grew so heated about modifying the ship at this stage that the Bureau of Construction threatened to cancel the vessel due to the added cost...however the builder recalculated the weights and stated that while the lengthening could have added speed, the weights were not an issue so the project continued at the design and the Texas, although having an extremely long build time nonetheless was delivered on it's original budget to it's original design. As it turned out the USS Texas might have used an extra knot or two during the Battle of Santiago in 1898 but the Battle turned out well in any event for the United States.
"If you want to build a ship, don't drum up people to collect wood and don't assign them tasks and work, but rather teach them to long for the endless immensity of the sea" --Antoine de Saint-Exupery
Probably also assign them tasks and work, or else *everyone* will go to collect wood without thinking about it and you'll deforest the surrounding area.
The fastest ship ship I've ever been on was the USS Carl Vincent. We were going WAY faster than the 32 knots Wikipedia says it capable of. Seriously. WAY faster than that. It was mind blowing. Aircraft Carriers can move.
I assume the trough shown in the resistance/speed chart found after Hull Speed must have a name? I don't think it is called "Sweet Spot." This appears to be where the ratio of fuel consumed and time expended in transit would be best for ships.
you might want to add, that to gain speed you need x times more power, that is a bigger reason why speeds are low. as for a 150 meter ship hull speed will be 29 knots but yet they sail 15. half of it. Also if you sail hull speed, with a wave top at bow and stern and a trough mid ships, you loose alot of stability. (not to mention bending moments that come into play at such situations)
20 yrs ago, My wife and I took a cruise from Vancouver BC to Hawaii on Princess cruise lines. The ship kept a steady spead of 24 knots for 2300 nautical miles to Nawiliwili on Kauai. When we docked, I got a chance to speak with a ship crew member while they were fueling. He said that they burned 800 tons of bunker oil. I told him that the trip was really smooth. He said that they cruise at that speed because its about physics and the hull design. He stated that the ship could go a little faster than that but, it would burn to much fuel. While we were underway ftom BC, we passed a smaller container ship under the Matson flag. Everything that YOU have stated here is CORRECT. Thank you sir!
I guess something could be said about fuel consumption? I assume the smaller vessels choose to run at a more optimal hull speed because it makes sense financially. Unless, they have a customer willing to pay the extra price for express delivery speed?
Me and my dad had almost identical boats the only difference was mine was 45’ where as his was 34’. For years how we couldn’t figure out why my boat was so much faster then his.
To misquote Einstein, once you've eliminated the identical, the rest --- however improbable --- must be the cause. As a software developer, I've learned never to assume I know _anything_ about the system I'm trying to fix, no matter how much experience I have with it.
but this is surely impossible to scale. they neeed to make a proportional 10x copy of a formula 1 boat and other speed boats to demonstrate the theory. and the power to weight/ size ratio must be equal.
I don’t even like ships, they scare me, but i’m such a geek that i can’t help being fascinated by all the technical elements and math involved. These video’s are amazing for people with a similarly geeky disposition as my own
Things scare me. Mostly, my fears are real possibilities, however improbable. A wise man told me that voluntarily facing my fears was the best way to diminish them.
Wait, so the local min is between Hull speed and Hump speed, but what is the effect of the waves on the boat that makes it face less resistance? It seems like you only talked about the speeds individually, but maybe I missed something I loved the bit about the bulbous bow, I had no idea that’s what that was for!
So I have no expertise or any knowledge about this subject, so I can't make any claims to the author of the video. BUT on doing a little research what I might ascertain is that the graph is shows applies to only a particular kind of boat (I can't find a similar graph anywhere, although it looks like this is not a hugely popularized field so I might just be bad at googling it). From what I've read, the right around the hull speed is going to be the true local minimum, although perhaps that's where things such as the bulbous bow come in, to stretch that minimum out before ascending the curve. It was an interesting topic to learn though, I'm electrical engineer so I missed out on all the fluid/mechanical goodies so I'm learning all the time on these topics! Let me know if you find out
This is so incredibly interesting. It's when water waves show their similarity to other kinds of quantum waveforms. Though, higher drag meaning higher hull speed is still confusing to me. All waves are disturbances in a system that transfer energy. Imagine if we could ride radiowaves, which can be MUCH longer than any water waves. It'd be like you're suddenly propelled 30 meters into the air without seeing anything, but you ready your antiparticle surfboard and ride this invisible wave until a mountain gets in your way. Or you accidentally leave the atmosphere and die.
On a related note, how much of a large ship's drag is from wave drag vs. viscous drag against the ship's hull? I always got the impression wave drag is the dominant factor. Thinking of viscous drag would be another factor in favor of larger ships, at least in terms of efficiency. More volume (mass, cargo volume, displacement) per surface area, assuming a similar shape.
Friction drag increases linearly with speed, wave drag increases with the square of speed. (Hull fouling from things like barnacles involves both, as the additional surface area of the protrusions increases friction, and each additional protrusion generates it's own wave.)
@@rydenkaye9735 Hull friction doesn't generate waves, it causes drag by another mechanism. Basically viscous friction between the ship and water causes a layer of water to be dragged along with the ship, which puts energy into the water and thus out of the ship, the engine needing to overcome this. Submarines have this, but don't have wave drag because they are too far from the surface to generate surface waves (hence, per displacement, submarines are actually more efficient, though with obvious other limitations and challenges).
Nice. I had some inkling of what is working here, but having it neatly encapsulated like this clarifies my thoughts and fills in the holes of my practical observations.
step one: get a big ship step two: apply for boat racing event step three: get rejected step four: say the a big ship is like a boat but bigger step five: they still reject you step six: give up
My favorite example of this is the j class sailboats which have a design rule to limit waterline length but adapted by adding overhangs that enter the water and increase waterline when the boat heels over
Has anyone taken a closer look at ancient sailing ships specifically from around Greece, Rome...basically the Mediterranean area? I noticed that some of those ships had a bow with a 90° square to the natural water flow where a bulbous bow should be. Kind of like a stop sign of sorts, only under water and having 4 sides instead of 6. That big under water square bow seems counterproductive to me but maybe the ancients living in the bronze age knew something about fluid dynamics that are simply beyond me.
@@cheveuxgraouh3821 Below the waterline?...and it was recessed a little behind the keel of the bow or figurehead (the ship I saw didn't have a figurehead). I think it was the Argus I was looking at but not sure.
Your videos have real peaked my interest into boats and sailing. I've never had any interest before this! I think I'm going to have a ask a friend with a boat to take me out so I can learn more!
Being bigger, it can hold more containers. More containers means more chance of them being red containers. Since red obviously = fast, this explains why.
Not really. Naval vessels are usually designed for 25+ knots nowadays. US nuclear carriers can make 33 knots so a Carrier Battle Group is designed with ships that can keep up.
@@kathibaba7665 those are top speeds, not cruise speeds. Of course top speeds are higher, especially for naval ships that usually have a fleet oiler/replenishment vessel nearby. For example the Kirov class battlecruisers have a cruising speed of 20 knots (nuclear), and Ticonderoga class cruisers have the same cruising speed (gas turbine)
I live very close to the St. Clair river and frequently watch the Great Lakes freighters over 1000 feet in length and the salties (smaller ocean ships) down to just a few hundred feet as they travel up and down the river and into the Great Lakes. For years I have wondered about the wave pattern as some ships would create a massive wave at certain speeds while others moving at the same speed would produce hardly any waves, yet the same ship would then produce a huge wake at a slightly different speed. I just assumed that it was cargo weight that accounted for this. Usually I notice 3 wake patterns as one comes from the bow, another set from mid ship and the last from the stern. This answered a lot of questions for me. Thanks for the video.
Kind of, in that increasing the size of the airplane increases the Reynolds number for a given speed, and things at higher reynolds numbers tend to have lightly lower drag coefficients. However, once you're at the scale of a small commuter plane drag from mach effects tends to be what limits your speed rather than the drag predicted for using the kind of incompressible flows the Reynolds number was modeled around.
I expect it is more complicated due to the way air is compressible and the density also varies greatly. It is why jets cruise at high altitudes - high altitude = less dense air = higher speed and lower fuel consumption. There is a trade off, if the fuel used to climb to high altitude is more than what you save by being at that altitude, then there is no point, so shorter journeys may have a lower cruising height than longer ones as they don't spend enough time at high altitude to make it worth while. Concord was much smaller than either, but cruised at higher altitude.
There's also the square cube law. Bigger ships have less surface area and cross section per unit volume, so if the same proportion of the ship is dedicated to engines, you have more power per unit of drag.
Great video! I have been fascinated with this since I was just a lad learning about the great America’s Cup yachts from back in the day. And about the simpler sloop I served on. :)
So how do we get this channel to blow up enough to have the budget to get a commerical carrier to plane just using jet engines? Bro, thats such an awesome idea!
Very good video. My earlier logic was that it has to be opposite. Bigger ships means bigger draws and therefore have to go slower. I was surpriced years ago that it was like told in this video. Could not understands why. Now i know
I have been watching videos all morning with juvenile, naiive, and even childish narration (all Yanks) Thank you for providing some 'science for adults'. Cheers. Peter D (a proud Britt.)
![Kodak Black - Versatile 4 [Official Video]](http://i.ytimg.com/vi/VcP_1Ua__vY/mqdefault.jpg)
As a Naval Architect, I really wish I had access to these videos when I started my degree. Such a practical demonstration of the theoretical concepts.
....plus you would have understood how critical it is for large ships to be able to get up on plane if they're going to be any good, especially with efficiency plus speed together. If 590-ton craft can leave the ground supported by nothing more than a gas, what's the hold up? How can we expect planing not to be standard on large vessels? 😊
@@ReflectedMiles sounds like you are suggesting hydrofoils. They are not efficient for larger ships. Please note my Naval Architectural degree is focused on plastic bathtub toys.
As a docking tug captain, this is cool to see in exactly the opposite way 😂 Practical demonstration is all we get.
Learning pressure zones on different hull forms is a very stressful experience.
@@krombopulosmichael6162 No in the video plane speed was beyond the hump speed where the wave peak is at the bow and the trough at the stern, so the engines push uphill in addition to water resistance.
@@RobBCactive most ships are not designed for plane speed though, according to the video. It does mention bulbous bows, which are becoming more common.
Thanks for the explanation. I've often wondered the same. Years ago, I was on a 42' private vessel crossing the Panama Canal. The Canal obviously has too much traffic to let a puny motoryacht take up an entire lock, so the Harbormaster put us in with a cargo vessel -- large, but sufficiently short to accomodate us both -- for each leg of the trip. On the way up, the big ship entered first, and we behind her. When we reached the lake elevation and that ship fired up her engines, her prop wash was so intense that the only thing keeping us from getting bashed into the sides of the lock were the six lines the Canal staff gave us (delivered by the famous "monkey fist") that held us tightly in the center. Still, all open beverages were immediately spilled. When she got underway and we followed, I was amazed at how quickly she put distance between the two vessels. In no time at all, we lost sight of her. Of course she made it across Gatun Lake in a fraction of the time it took us. The Canal staff knew this would happen, so they had previously scheduled us for a departure with a different vessel. This time, her length wasn't an issue, as they put us in ahead of her, and her bow literally covered the space we occupied. You don't truly get a sense of the scale of these beasts until you have looked straight up from the deck of your boat and seen nothing but metal above your head.
The worlds most expensive parasol
It’s hard to imagine taking a 42-foot vessel through the PC. It definitely would’ve been a fascinating and memorable adventure.
@@bnease007, it sure was!
@@bnease007 Taking any vessel through the first time is memorable and fascinating.
I have a ship's bell from the Panama Canal. Weighs about 400 pounds.
I live 800 miles from an ocean, and yet I find your videos fascinating, including this one. Cheers!
Now try living on the water and never taking a job or learn how to drive big boats and ships and watch these videos. I'm In my 30's and love these videos I wanna change my career. cheers
Growing up on an island (and living on another) I've never felt the ocean not relevant. I wonder what it's like to live so far inland.
I live 8 miles from an ocean, and yet still find this videos fascinating.
Fuckin' SAME. I'm a landlubber who's lived in the desert my whole life
I live 800 miles from land. I've never even seen the land before.
wow, I think this is the first time in my life, where someone used the term "wave length" and is actually talking about waves. (I am an audio engineer with a fable for physics, and I know, that those other waves are waves, too... but you know what I mean)
And also, that was an utterly interesting video, thanks, I learned a lot^^
same but for me light waves/ radiation funny how that feels!
same here - electrical engineer
Me Too..............I'm a Glove maker !
Light and Audio-waves are "real" waves too!
@@prototypeinheritance515 yea, that's exactly what I said🙃
I spent 23 years on aircraft carriers. Being retired, I now work around a lot of Airforce dudes. None of them believe me when I tell them carriers are the fastest ships in the fleet.
Yeah, that's not how it works in the video games, either! 😂
People see that big wide flight deck and ignore the narrow beam at the water line. Probably understandable I guess
@@timjohnun4297 😂
@@hawkeyeted Why are you angry or surprised that video games are wrong?
@@jpaugh64
Why are you here chirping about stuff you know nothing about?
Really appreciate that this video is pure information. no sponsorship, no Patreon pitch, no asking to subscribe
Not for nothing but industrial accident recreation videos are interesting, informative and useful tools to prevent future avoidable accidents
Is there something wrong about sponsorship, patreon pitch, and a very humble ask for subscibing?
@@jorditakarbessy8547 they are not wrong but they get in the way of learning. So it's awesome when a youtuber can make ends meet without them
Those jet engines on the ship are 100% what I would do If Kerbal had sea fairing vessels.
Trent turbines are used to power both aircrafts and ships
in fact there are many ship gas turbines that share most of their parts with airliner jet engines.
Some US Navy vessels have turbine engines. Envy? LOL
Have a look at Russia's Ekranoplan flying boats
That’s what the fishing boat needs 😆
1. the sheer wealth of knowledge these days
2. the WAY its presented: video plus clear&concise video
I was thinking it was due to a ship 2* as long, wide, and tall having 4* the surface area (for drag), yet having an engine 8* as powerful. Didn't think about the wave interference. Good video
i did too. thought it had to do with how a bigger engine takes more fuel but also the bigger ships caries exponentially more containers.
@@ronblack7870 Not exponentially, but cubic more containers. Length*Width*Height.
A boat twice as long is 8 times bigger. L x B x H.
@@sverkeren A cube power is an exponent.
This is what interesting is that hull speed is determined by the length of the ship, not area.
Informative, no nonsense, and very well structured for my layman mind to understand. You run a phenomenal channel and are a great teacher. Thank you!
Yep
As a retired Captain now involved in ship construction I find this presentation fantastic. Thanks for sharing, keep up the good work.
You could easily expand this video with the hull shape aspect alone, ldl hulls are faster and lower fuel costs.
a good example, an 85' loa motor yacht with a draft of 4 feet designed for displacement cruising. Top speed is 18 knots, cruising speed is 15 knots. 15 knots speed gives her 1,500 nm range on 1000 US gallons of diesel, 18 knots gets you 500 nm from the same quantity of fuel.
These same factors are in play with the big cargo ships, yet most people can relate to being told if they slow down by 5 miles an hour they will travel 1000 miles further in their pleasure boat over it's cheaper to ship a 6 week trip than a 1 month trip for your overseas delivery..
*ldl = low displacement length.
500 nano-metres! Wow that's inefficient!
@@Azettler1 nautical miles
@@jaquigreenlees I knew what the acronym was for and was just bugging. I find it funny that we have two measures of distance that have the same unit label :)
4:40
"But of course that isn't the hull story."
Proceeds to give talk about the Hull design.
Nice.
And i thought it was just about momentum
Wow. Great video. I’m completely land locked but totally in love with the ocean. Just amazing information. Mind is blown right now
Yep
it maybe of interest: the bulbous bow works only at a limited range of speeds, because its wave has to interfere as designed with the normal bow-wave. Cargo ship hulls (including the bow-shape) are designed for a resonable range of cruising speed, to be fuel efficient. Intrestingly you can guess a ships speed by looking at its generated wave lenght at the hull. you only need to know how long the ship is, judge the length of the wave and use the formula depicted in the video to calculate the speed of the ship (through the water) ...
Your explantion/guess,
does not include water conditions.
All vessels:
would be much better with a nose bulb !
-- Better for control of spin & steering;
-- Keeping hull at a reasonable angle compared to the water surface.
-- Better dispersing of the bow's wave.
******
>> A Hydro-plane:
-- can achieve higher speeds;
-- has less danger of flipping over.
( compares to many automobiles that save gas, with 500lb -- 200 kg of cement inside the rear trunk ! )
@@dirkkarmel5209 how would adding weight in your trunk improve efficiency??
Dumbest comment I’ve ever read. Try strapping a bulb to any type of Planing hull and let me know how it goes
Wouldn't it be way easier to just guess the speed than to guess the wave length AND guess the length of the hull to calculate the speed?
Beautifully explained. I’ve heard the waterline length rule touted for years and only recently learned it was due to a longer wavelength of bow and stern waves. You closed the loop for me, easily explaining that the wavelength was itself proportional to speed. Thank you!
Assuming the ship is travelling against and into waves, of course.
More often - for speed and efficiency - it'll travel with the waves whenever possible.
Sometimes it'll have to travel across the waves, winds and currents don't always end at your planned destination.
Sometimes the waters will be calm. Making the hull bulb counterproductive, if anything.
I've seen a boat running at "hump speed" before, a motor yacht. even to my untrained eye, it looked horribly inefficient, like the boat was trying to climb a hill.
another term for that is transition wake, and yes it's very inefficiant
In quotes? You don't think that's the real term?
@@HelloKittyFanMan. Adding quotes like these usually implies fake, but it can also mean a special or unique phrase. Clearly it's the latter in this case.
No, @@DemPilafian, it was _not_ clear, because if it was then I wouldn't have asked about it. Do you mean like... emphasis?
Because if that's what you're trying to say, then you'd be wrong. Because if that is what you're trying to say, then my reply to that is that no, quotation marks are not emphasis marks, or they would be called "emphasis marks" alternately. That's not now, nor was it ever, their job. How anyone would've ever gotten taught that in some presumed "official" way completely baffles me! Emphasis is already handled by *boldness,* _italics
@@HelloKittyFanMan. You should have put your entire 2 page reply inside of quotes.
I used to sail small boats as a teenager, and despite not knowing how any of this worked I remember intuitively feeling the phenomenon of hump speed and planing. Especially the boat 'falling' off the top of a wave, going from planing to hump speed, as a gust of wind dies off. Super facinating to learn how this actually works!
And then you get on a keelboat, which cannot plane, and it does not matter whether the wind is 10 or 20 knots, you can't move any faster ....
You can plane in keelboats my friend, you just haven’t been racing the right ones!
@@rydenkaye9735 You need foils for that :)
Same thing with adjusting the trim on a power boat. At a certain speed and perfect trim, you can just feel the resistance leave and the boat levels out.
Exactly this
also worth mentioning: the drag force is proportional to the cross sectional area of the ship. by the square-cube law, doubling the scale of a vessel will quadruple the drag, but allow 8 times the internal volume for engines to be put in. thus, if your engines take up the same amount of space, you'll have twice the power, and sqrt(2) times the speed
Very happy about your new pace of publication, especially seeing that the quality of the videos didn't go down a notch! Good work!
I sailed on VLCCs in the '70s and their top speed was 15 knots. During the oil crisis we never sailed faster than 8 knots.
Bruce 🧐
I heard a story about a US navy carrier group deciding to have a drag race for amusement. As expected the smaller ships got the jump at the start, but it was not long before the carrier caught up and passed every other boat…much longer hull length.
that must have been the most expensive (amount of oil burned apart from the nuclear carrier) drag race in history!
@@Digi20 probably
the Carrier always wins!
@@Digi20 it happens every cruise.
Well, I suppose they don’t call it plane speed for nothing
This was extremely informative! One of my favourites of this channel so far. Very well explained and so interesting.
Excellent video, I heard the term "Hull speed" but nobody had a good explanation as you put it here as to what happens.
Keep up the good videos and knowledge spreading you do!
As an instructor of maritime topics, thank you for another video that makes me really think!
I did not know the hull speed formula. It's nice to see it confirming my guesstimated speeds for my D&D ship's speed tho (130 ft 3 masted schooner at waterline, assumed her top speed to be around 12 knots. Which is less than hull speed, but considering wind and stuff it's within ballpark!)
Brilliant as always. I just really enjoy how he doesn’t talk down to his audience. I learnt something watching this…thank you.
Overcoming the hump speed is mechanically the same as breaking the sound barrier.
You wffectivly turn a wave into a straight line, saving tons of energy.
But it needs tons of energy to overcome the hump/barrier first.
And even then it needs more energy then any speed that doesnt approach thr hump/barrier.
There are other ways to defeat the wave effects. Tuning shapes of leading and trailing edges to better suit lamellar flows back into the common plane on the trailing edge is the major factor. Shorter hulls can be made efficient at higher speeds but compromises are often made to achieve other desirable effects. This video however is a good beginner primer for this niche of fluid dynamics.
I thought as much, and thought of the same analogy.
"Needs more energy than any speed that doesn't approach the hump barrier." Every time you accelerate from zero, you're approaching the hump barrier. I know you're talking about it as a limit from Calculus, but how close to the hump barrier does it have to be for that factoid to lose veracity? 70%? 40%?
Actually, Real Engineering shows a graph of drag vs mach number, and it clearly shows that mach 1 is a peak, and by mach 6, the drag is significantly lower.
He was taking about rockets (which are designed to go faster than MACH 1), so I'm not sure if his graph was generally applicable to hurled objects or not.
He was discussing the new startup with rockets whose "first stage" is a centrifugal slingshot. I can't remember the video title.
Very interesting, and very clear! In case you were wondering whether a longer, more detailed video on this topic would find its audience, know that you'd have at least one enthusiastic viewer.
Still awaiting that tugboat video.
It'll be epic. Because tugboats are epic.
I like how you answered the question again but this time with the context of everything we're talking about so the more literal explanation makes more sense. Great way to sum it up at the end of the video.
I had assumed this was just going to be a fairly straightforward square-cube thing, where the drag on the ship scales with the surface area of the ship but the size of the engine it can hold scales more with the volume
I would expect the engine size to scale with the economic utility of the cargo ship --- which would scale with it's volume.
Hull shape!
When I was in maritime school, this crazy old ex-Navy captain used to tell us, "whatever the question is, the answer's usually hull shape." And it's pretty close to correct, although he didn't like it much when the least-mature adult in the class tried to turn that into a running gag.
That ex-captain never could get me to understand hull speed, though, and I never really understood the physics behind planing and the way a small craft's bow rises out of the water at hump speed. Never heard the term "hump speed" before. I've never been able to find this stuff in the American Seaman's Manual, either. But thanks to Casual Navigation, it all makes perfect sense. This is a gem of a video.
And then we have the bonus of a big container ship getting up on a plane, and then being fitted with giant jet engines. That made me smile.
As a random guy on the internet I have to say this is absolutely facinating so congrats to y'all naval engineers who choose an interesting major
Going into this, I thought it would be a matter of larger ships having larger, more powerful engines. That's a really interesting cause, though, and it shows just how much thought goes into every aspect of sailing.
Well, obviously, larger (or underpowered) engines would have an effect. Also, does this rule work as well for pleasure and military ships, where finding the maximally efficient speed is not the most important criterion?
The question at the beginning of his video is not well stated, so I'm not sure exactly what I learned.
Exactly! Thank you. Everyone else seems to be going along with this unclear premise without questioning it.
I was under the impression that the hull speed was the last efficient speed (assuming a slippery hull) before the "wall" of resistance you get as you approach hump speed, due the destructive wave interference outlined in the video. So in the graph it would be found at the bottom of the little dip rather than at the hill before it.
You can think of the hump speed as a kind of trailing vacuum effect as an analogy.
There's a similar phenomenon with the speed of sound. Crossing it causes peak air resistance, but for a plane or rocket that's designed for it, going faster than MACH 1 decreases your air resistance the faster you go. So, for an aircraft, MACH 1 is the least efficient possible speed, compared to any other.
I went fishing a lot growing up with my Dad in our 19ft jet boat, I’d always wondered why the boat pitched and accelerated differently before the boat got on step, and how it would fall off step. this makes perfect sense
Perfect timing. I was bored so this is great
I really enjoy your work and efforts uploading these, not too technical and not too simplistic. 👍❤️🇬🇧
Why is a longer boat faster than a smaller one? Because the front is closer to it's destination.
It's been short aeons.....till the term "wavelength" made this much sense to me! Thanks a bunch👍
Finally i understand why my uncle always told me it's better to go fast with the boat so it starts planing!
Glad to see your method of reducing the condition, for the average person to understand.
*********
Beyond the hull waves, there are other factors that apply:
-- Water surface conditons;
-- Wind conditions;
-- Water currents;
-- Ship's acceleration/deceration.
-- Angle against water of ship's bow,
VS the ship's stern.
In a smaller vessel:
these quickly Add up !
--- The vessel, quickly becomes unstable !
--- Can easily flip over, in any direction !
( Bow going under the Stern,
being least likely,
frequently does occur during
bad ocean conditions ! )
In a larger vessel:
-- These factors, are minor;
-- Once up to speed, is very hard to change speeds or direction;
-- Being longer & heavier, reduced dangers from waves;
-- A skilled captain: can even use ocean waves, to their advantage.
( Using less engine power,
to reach higher speeds. )
Informative video. Could you please cover the large, high speed, passenger catamarans invented by Incat in 1990 and developments of that design such as the Austal trimaran you showed at the end of this video? I've always been amazed that craft over 100 metres long can travel at up to 50 knots and still be commercially succesful.
Now that's tax money at work i would like to see
Drag vs stability.
Catamarans and Trimarans are very stable, even they hardly touch the water.
Every now and again the RUclips recommendation algorithm comes up with a real gem. Subscribed.
Back around 1890 when they were building the first USS Texas battleship an argument ensued with the designer, the Bureau of Construction, and the actual builder. There were worries that the weight calculations of the ship had been in error and the builder suggested that the ship be made ten feet longer but the keel had already been laid (but could have been modified at extra cost). The builder said that the ship would have the added benefit of being faster as a result. However, the argument grew so heated about modifying the ship at this stage that the Bureau of Construction threatened to cancel the vessel due to the added cost...however the builder recalculated the weights and stated that while the lengthening could have added speed, the weights were not an issue so the project continued at the design and the Texas, although having an extremely long build time nonetheless was delivered on it's original budget to it's original design. As it turned out the USS Texas might have used an extra knot or two during the Battle of Santiago in 1898 but the Battle turned out well in any event for the United States.
"If you want to build a ship, don't drum up people to collect wood and don't assign them tasks and work, but rather teach them to long for the endless immensity of the sea"
--Antoine de Saint-Exupery
All of which has nothing to do with the video.
Probably also assign them tasks and work, or else *everyone* will go to collect wood without thinking about it and you'll deforest the surrounding area.
@@jamesrodgers3132 that's like saying poetry has no practical applications :}
@@jamesrodgers3132 I'm glad I'm not the only one who noticed.
what the fuck is an ark ? Noah
I love how these videos are extremely educational and are practically like having a real “ship” course.
The fastest ship ship I've ever been on was the USS Carl Vincent. We were going WAY faster than the 32 knots Wikipedia says it capable of. Seriously. WAY faster than that. It was mind blowing.
Aircraft Carriers can move.
I assume the trough shown in the resistance/speed chart found after Hull Speed must have a name? I don't think it is called "Sweet Spot." This appears to be where the ratio of fuel consumed and time expended in transit would be best for ships.
you might want to add, that to gain speed you need x times more power, that is a bigger reason why speeds are low.
as for a 150 meter ship hull speed will be 29 knots but yet they sail 15. half of it.
Also if you sail hull speed, with a wave top at bow and stern and a trough mid ships, you loose alot of stability. (not to mention bending moments that come into play at such situations)
He covers that in another video: ruclips.net/video/YPQY70z5uKE/видео.html
Yes, the middle of your ship sagging can end very badly...
Great, now you've got me visualizing a cargo ship planing the waves like a speed boat by force of several strapped on jet engines.
omg, I always wandered and never understood why boats had that feeling during some acceleration/deceleration process... thank you so much!
20 yrs ago, My wife and I took a cruise from Vancouver BC to Hawaii on Princess cruise lines.
The ship kept a steady spead of 24 knots for 2300 nautical miles to Nawiliwili on Kauai.
When we docked, I got a chance to speak with a ship crew member while they were fueling.
He said that they burned 800 tons of bunker oil.
I told him that the trip was really smooth.
He said that they cruise at that speed because its about physics and the hull design.
He stated that the ship could go a little faster than that but, it would burn to much fuel.
While we were underway ftom BC, we passed a smaller container ship under the Matson flag.
Everything that YOU have stated here is CORRECT.
Thank you sir!
Always a treat. Keep making these!
I guess something could be said about fuel consumption? I assume the smaller vessels choose to run at a more optimal hull speed because it makes sense financially. Unless, they have a customer willing to pay the extra price for express delivery speed?
Hmm 🤔
All the info I needed about something I have no practical use for. Subscribed
Me and my dad had almost identical boats the only difference was mine was 45’ where as his was 34’. For years how we couldn’t figure out why my boat was so much faster then his.
To misquote Einstein, once you've eliminated the identical, the rest --- however improbable --- must be the cause. As a software developer, I've learned never to assume I know _anything_ about the system I'm trying to fix, no matter how much experience I have with it.
but this is surely impossible to scale. they neeed to make a proportional 10x copy of a formula 1 boat and other speed boats to demonstrate the theory. and the power to weight/ size ratio must be equal.
I don’t even like ships, they scare me, but i’m such a geek that i can’t help being fascinated by all the technical elements and math involved.
These video’s are amazing for people with a similarly geeky disposition as my own
Things scare me. Mostly, my fears are real possibilities, however improbable. A wise man told me that voluntarily facing my fears was the best way to diminish them.
"A ship is just a hull displacing water."
Dictionary of Casual Navigation
As a mechanical engineering student I found this video super interesting! Love your content!
Now I want to see a cargo ship planing.
I had to laugh out loud when I saw that massive commercial cargo vessel using the engines to start "climbing"!
Wait, so the local min is between Hull speed and Hump speed, but what is the effect of the waves on the boat that makes it face less resistance? It seems like you only talked about the speeds individually, but maybe I missed something
I loved the bit about the bulbous bow, I had no idea that’s what that was for!
So I have no expertise or any knowledge about this subject, so I can't make any claims to the author of the video. BUT on doing a little research what I might ascertain is that the graph is shows applies to only a particular kind of boat (I can't find a similar graph anywhere, although it looks like this is not a hugely popularized field so I might just be bad at googling it). From what I've read, the right around the hull speed is going to be the true local minimum, although perhaps that's where things such as the bulbous bow come in, to stretch that minimum out before ascending the curve.
It was an interesting topic to learn though, I'm electrical engineer so I missed out on all the fluid/mechanical goodies so I'm learning all the time on these topics! Let me know if you find out
This is so incredibly interesting. It's when water waves show their similarity to other kinds of quantum waveforms. Though, higher drag meaning higher hull speed is still confusing to me.
All waves are disturbances in a system that transfer energy. Imagine if we could ride radiowaves, which can be MUCH longer than any water waves. It'd be like you're suddenly propelled 30 meters into the air without seeing anything, but you ready your antiparticle surfboard and ride this invisible wave until a mountain gets in your way. Or you accidentally leave the atmosphere and die.
On a related note, how much of a large ship's drag is from wave drag vs. viscous drag against the ship's hull? I always got the impression wave drag is the dominant factor. Thinking of viscous drag would be another factor in favor of larger ships, at least in terms of efficiency. More volume (mass, cargo volume, displacement) per surface area, assuming a similar shape.
Friction drag increases linearly with speed, wave drag increases with the square of speed.
(Hull fouling from things like barnacles involves both, as the additional surface area of the protrusions increases friction, and each additional protrusion generates it's own wave.)
Hull friction barely effects wake lol the waves generated by a individual barnacle are negligible compared to the tons of metal displacing water
@@rydenkaye9735 Hull friction doesn't generate waves, it causes drag by another mechanism. Basically viscous friction between the ship and water causes a layer of water to be dragged along with the ship, which puts energy into the water and thus out of the ship, the engine needing to overcome this. Submarines have this, but don't have wave drag because they are too far from the surface to generate surface waves (hence, per displacement, submarines are actually more efficient, though with obvious other limitations and challenges).
@@quillmaurer6563 i think a submarine generates waves as well, you just can't see them
Nice.
I had some inkling of what is working here, but having it neatly encapsulated like this clarifies my thoughts and fills in the holes of my practical observations.
step one: get a big ship
step two: apply for boat racing event
step three: get rejected
step four: say the a big ship is like a boat but bigger
step five: they still reject you
step six: give up
step seven: try to run it anyway
step eight: run aground because the course is to shallow
step nine: dredge a deeper race course
step ten: get smoked by a hydrofoil anyway
My favorite example of this is the j class sailboats which have a design rule to limit waterline length but adapted by adding overhangs that enter the water and increase waterline when the boat heels over
is hump speed how quickly a ship makes lifeboats?
that thumbnail is wild
Has anyone taken a closer look at ancient sailing ships specifically from around Greece, Rome...basically the Mediterranean area? I noticed that some of those ships had a bow with a 90° square to the natural water flow where a bulbous bow should be. Kind of like a stop sign of sorts, only under water and having 4 sides instead of 6. That big under water square bow seems counterproductive to me but maybe the ancients living in the bronze age knew something about fluid dynamics that are simply beyond me.
It's a ram, it's not made simply to go through water, it needs to go through other ships too.
@@cheveuxgraouh3821 Below the waterline?...and it was recessed a little behind the keel of the bow or figurehead (the ship I saw didn't have a figurehead). I think it was the Argus I was looking at but not sure.
@@cliffcampbell8827 yes, so you make a hole in an other ship below the waterline and make it sink
Your videos have real peaked my interest into boats and sailing. I've never had any interest before this! I think I'm going to have a ask a friend with a boat to take me out so I can learn more!
The big'uns generally tend to have a faster 'hump speed', in my experience.
Being bigger, it can hold more containers. More containers means more chance of them being red containers. Since red obviously = fast, this explains why.
25 knots? Jesus, that's faster than many naval capital ships
Not really. Naval vessels are usually designed for 25+ knots nowadays. US nuclear carriers can make 33 knots so a Carrier Battle Group is designed with ships that can keep up.
@@kathibaba7665 those are top speeds, not cruise speeds. Of course top speeds are higher, especially for naval ships that usually have a fleet oiler/replenishment vessel nearby. For example the Kirov class battlecruisers have a cruising speed of 20 knots (nuclear), and Ticonderoga class cruisers have the same cruising speed (gas turbine)
I live very close to the St. Clair river and frequently watch the Great Lakes freighters over 1000 feet in length and the salties (smaller ocean ships) down to just a few hundred feet as they travel up and down the river and into the Great Lakes. For years I have wondered about the wave pattern as some ships would create a massive wave at certain speeds while others moving at the same speed would produce hardly any waves, yet the same ship would then produce a huge wake at a slightly different speed. I just assumed that it was cargo weight that accounted for this. Usually I notice 3 wake patterns as one comes from the bow, another set from mid ship and the last from the stern. This answered a lot of questions for me. Thanks for the video.
Does a similar thing apply to airplanes?
For example, the 747 max speed is faster than the smaller 737.
I would imagine that it would hold true, although the densities of the two fluids are substantually different.
Kind of, in that increasing the size of the airplane increases the Reynolds number for a given speed, and things at higher reynolds numbers tend to have lightly lower drag coefficients. However, once you're at the scale of a small commuter plane drag from mach effects tends to be what limits your speed rather than the drag predicted for using the kind of incompressible flows the Reynolds number was modeled around.
I expect it is more complicated due to the way air is compressible and the density also varies greatly. It is why jets cruise at high altitudes - high altitude = less dense air = higher speed and lower fuel consumption. There is a trade off, if the fuel used to climb to high altitude is more than what you save by being at that altitude, then there is no point, so shorter journeys may have a lower cruising height than longer ones as they don't spend enough time at high altitude to make it worth while. Concord was much smaller than either, but cruised at higher altitude.
@@chuckaddison5134 same problem
evan if water/air 800 times different.
I'm not in any kind of naval anything yet I watch every video over time haha. I'm a pilot and I watch ship videos 😮
Hump speed 🧐
There's also the square cube law. Bigger ships have less surface area and cross section per unit volume, so if the same proportion of the ship is dedicated to engines, you have more power per unit of drag.
Strap on a few jet plane engines lol
Fascinating. Thanks random RUclips recommend and the people that produced this excellent video!
Naval architects in my country had the adage: _Länge läuft_
(loosely translates to length runs)
2:54 being an engineer from europe that one hurt.
I've been boating my entire life and this just blew my mind.
Keep up the great work! Love your voice! 😍
I'm not surprised. A jet can go literally twice as fast as one of my paper airplanes.
If your paper airplane airline serves good food, I'd still fly with you. 👍🛫
The last ten seconds answered the question, and I'm so glad I stayed until then.
Great video! I have been fascinated with this since I was just a lad learning about the great America’s Cup yachts from back in the day. And about the simpler sloop I served on. :)
So how do we get this channel to blow up enough to have the budget to get a commerical carrier to plane just using jet engines?
Bro, thats such an awesome idea!
Very good video. My earlier logic was that it has to be opposite. Bigger ships means bigger draws and therefore have to go slower. I was surpriced years ago that it was like told in this video. Could not understands why. Now i know
I didn't ever expected ships to be that interesting. You do an awesome job. Thank you :*
I have learned much and will now calculate the optimal wake surf speed for my boat thank you.
I live in a landlocked country, but i really enjoyed this 👍
That was a HULL of a good explanation.
Thanks for making these purely informative videos. So cool when mathematical concepts appear so clearly like this!
I have been watching videos all morning with juvenile, naiive, and even childish narration (all Yanks) Thank you for providing some 'science for adults'. Cheers.
Peter D (a proud Britt.)
This has to be your best video yet!!
Well there's an answer to a question I never had, I appreciate this new knowledge.