Why Don't Tugs Turn Ships?
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- Опубліковано 14 жов 2024
- ✩ABOUT THIS VIDEO✩
In this video, we investigate the effect of the pivot point when it comes to manoeuvring large ships. We explain how pivot point theory gives us a good explanation of the effects, but also show you the underlying forces at play so that you can get a deeper understanding of the principles.
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All content on this channel is provided for entertainment purposes only. Although every effort has been made to ensure the content is accurate and up to date, it remains the responsibility of the viewer to determine its accuracy and validity. The content should never be used to substitute professional advice or education.
Thank you for making it complicated in an understandable way.
well said lol. honestly, most of our brains are great at these sort of analog changing calculations with some real-world practice. it's just the physics behind them that's insane.
Ships are a whole lot more complicated than I thought
Don't you mean: a _hull_ lot more complicated...
@@leocelentebooooooo
Big piece of curved metal floating
Fluid dynamics are very complicated.
@@leocelenteI wonder if he gave you a stern look following that comment?
I think one big reason large ships appears to have so many counterintuitive handling characteristics isn't actually that their handling is really more complicated than smaller vessels and vehicles (though they might also be large enough that some proportionally weak effects are noticeable, too); I think one of the main reasons is that they are so large that everything seems to happen in "slow motion" which means you can't just react to how it feels in real time, you have to plan things several minutes ahead.
Bicycles also have really complex physics with weird gyroscopic effects and positive and negative feedback effects (there's a reason it takes quite a while to master it) but it's so small that everything happens in terms of milliseconds and seconds rather than minutes and hours like a ship; which means you can fairly easily train your preexisting brain circuitry for balancing on two legs to instinctively react and compensate for all the odd bike physics. But things that are so slow that you have to apply the steering inputs for several seconds before they even start to have an effect and for minutes before they start to be noticeable is simply too slow to be able to use your normal movement circuitry and you have to calculate and plan everything consciously rather than just reacting instinctively.
(Admittedly I haven't tried steering a big ship; but I have tried steering my brothers wooden boat with an inboard engine (no idea about feet but it's much bigger than a van but shorter than a bus, I think?), which is large enough that it's at the limit of how big it can be and still possible to steer instinctively. With bikes and most cars you can easily just hold the steering wheel and look where you want to go and your arms will make hundreds of microscopic adjustments seemingly on their own so that you appear to drive straight even on a slightly bumpy road, while with this boat I would suddenly notice I was veering slightly to port and apply rudder towards starboard and then a few seconds later notice I was starting to veer too far to starboard and so I had to more consciously apply just an imperceptible correction and then trust that it will start to have an effect in a few seconds. Otherwise I would be zig zagging all the time. But I feel it's still within the size that you can eventually start to develop a feel for it without having to think so much about it; but I doubt that is true for even larger vessels. I assume you have to more deliberately measure your current heading and the difference from your desired heading and then calculate an appropriate degrees of rudder input or engine power to apply for some amount of time (or use a lookup table of precalculated values) rather than just feeling it.
I guess the closest you get to sailing big ships on instinct is to build a mental model of the movement that you can run faster in your mind so that you can engage your intuition on the mental model?
Yes and no... it feels much, much faster from the bridge. Yes, some responses take longer, but the rub has more to do with the fact that we're trying to work 2-3 movements in advance, in my opinion. There's also the fact that the distances involved are at greater than human scale. I'd add that there's a lot more boat for the environment to work on, which is going to make each experience more unique, plus the power involved increases bottom, bank, and intership interactions to account for. Finally, on a small boat you're basically always driving the same boat. Maybe an extra few passengers, but that's a much smaller difference than fully loaded vs. lightship.
Ultimately, it's correct to say that it's all intuitive, it just takes a bit more education and experience to get there.
The point about time of feedback is a really neat one.
You sound like you never driven a car on the limit on snow before. In rally racing you have to use instincts and conscious thought to not only win but also not to crash and die. This is why rally drivers have co-drivers/navigators to let them know what is ahead because you need to pre-plan when you need to brake, steer and give throttle several turns ahead.
@@toolbaggers Isn't that completely consistent with SteinGaus's point? No one spends that much time driving on snow like they do in regular driving. And moreover, it has the opposite problem of too long feedback times- the feedback times are incredibly short, even shorter than a human can normally react to.
then you add on tide wind and or bank effect then Murphey's law might pop up as well
Like a whale stuck on the bulbous bow. 😂
Murphy's law implies a potentially non-zero coefficient for each term of any equation. 😉
@@brettany_renee_blatchley ...and of course those coefficients' change rate is dependent on how consequential and inconvenient a failure would be to the ship's master. 😝
@@KonradTheWizzardAnd exponentially proportional to the number of people watching! 😂👍
@@BobHill-s2c And also like when a whelk is wedged within the wheelhouse 🐚
I'm certainly acquiring lots of good sailor talk with more than four letters these days!
Reminds me of how a surfboard works. You can feel this piviot theory when you push your foot down/sideways to initiate a turn.
A lot of the hull theory on this channel reminds me of being in the shaping room
Even removing the effects of water and all that, and just taking the simplest physical model of an extended rigid body, working out what component of a force causes translational acceleration and what component rotational is surprisingly counter-intuitive. The maths isn't all that complicated, but it's hard to picture something speeding up both its sliding and its spinning simultaneously. Add in multiple forces acting at different points and it very quickly leaves what my intuition can cope with.
Like learning to back a trailer. Not that complicated, but intuition interfering with understanding. Much more complicated with water being the medium however.
I read a book by John McPhee called "Common Carriers" that has a chapter about ships and fluid dynamics. I've had some experience with river-rafting, and there seems to be a tendency for water to push to where one does not want to go.
Turning a boat isn't as hard as predicting the weather.
@@toolbaggers Don't need no calculus. A little trig might help though.
This is by far one of the most underrated marine transportation knowledge channels on UA-cam. Not going to lie
The transition at 2:09 is FANTASTIC. Even before you offer the explanation, we begin to have an intuitive understanding of why ships turn when tugs push their center. This is why I watch this channel
This reminds me a lot of the explanation of how a motorcycle turns by leaning and counter steering.
Non drivers get confused of why you would push the side you wanna turn
Yes! But bikes are small enough that you eventually train your brain to do it instinctively; because everything happens at a time scale our brain is built for; while ships with it's enormous size requires maneurvres that last minutes, way longer than our brains are able to just do by feel. (Or at least by the time you start to physically feel the ship is turning too much or too little you are several minutes too late to do something about it)
@@SteinGauslaaStrindhaug bruh imagine i need to actually think for minutes how to lean that shitbox in. On the other Hand you really need to predict the corner and lean accordingly in + you need the right speed or else its lame.
I drive a supersport and for me its always a balance act on how fast can i take the corner without crashing and then i try to take that.
Plus ships barely do turns that they dont see, sometimes corners on street begin very straight and then get very tight, or worst case a normal 60-70 corner ending in a 180 corner which we have sadly a lot in the mountains
The same is also sort of true for go-karts. One way to handle a go-kart is to set the rear loose into a corner, by leaning and using the shift in balance as you brake, and then lightly counter steer through the corner itself. The slip angle lets you maintain a bit of speed into the corner, and then depending on the actual corner lets you set up for exit sooner.
@@SteinGauslaaStrindhaug People who move from bicycles to motorcycles sometimes get into trouble because of the weight difference. With a bike you can turn pretty effectively just by leaning to shift your body weight; but a heavy motorcycle will turn in very slowly if you do that. It's necessary to consciously counter-steer to establish a lean angle.
I've been wondering why the pivot point moves with the ships motion for as long as I've known about the phenomenon. No one has been able to explain it, until now! Thank you! It was a legit thrill to learn this :)
I had to pause the video the moment you said "moving into still water", and make sure I understood.
nice. I love it when the reason isn't something i'd correctly guessed, and you consistently deliver on that front :D
That illustration was cool. The bow thruster thrusts to starboard, so the stern wants to kick out to port. To counteract that, we obviously steer with the rudder.. to port...
That was superb! A clear explanation that is easy to follow and ends up almost being intuitive. Possibly one of the best explainers I've watched on YT 🤓👍
I've been watching your videos for about a year now. I never had any interest at all in the subject you talk about but now I love seeing a new video from you. Fantastically well explained videos. Cheers.
4:02 -- i appreciate you putting Warren Zevon's "DAH!" from Werewolves of London in there
I know nothing about sailing or boats, but I love this channel so much.
Great job!
that was really good explained and also if I think about it, makes it pretty clear on how a ship with a bow thruster can move sideways - parallel - onto a dock
The part about bow thrusters is very important knowledge for mates of workboats. Any mate in Fourchon can tell you that they'd rather drive in reverse. Most think it's primarily because they can see more of the boat in the tight turns and narrow passages, but it puts your very strong z-drive on a shorter lever arm and your relatively weak bow thruster on a very long arm (plus the reduction of hull interaction).
I thought that was a ram chip in the thumbnails 😂
What’s a ram chip!?
HMS DDR5
@@taeliantalittia612 😂
I just saw it
Man the bow thruster explaination maked so much sense now!
It's a little bit like centrifugal force. People will say it doesn't exist, but if you construct the force diagram in a rotating frame of reference there is clearly a force vector pointing away from the center, and the clothes in your clothes washer clearly get mashed up against the outside of the drum during the spin cycle.
Fluid dynamics aside, there are similarities with learning how to back a motor vehicle. especially with a trailer. Intuition can be mistaken.
Thank you for the detailed explanation. I love the nautical theme.
A imperfect theory will shine when you in a environment with imperfect data measurement.
Like why you have soft fingers, its hard moving you hands and garbing objects, much easier to have soft fingers that just deform and grip on to any object.
But you also have a hard time being precise because of it.
Were a robot with metal fingers can be super precise but also fails the moment something gose wrong.
So it makes sens that you can used a broken incorrect theory as replacement, when there always gonna be so many factors that you cant control anyways.
Its a thing people (especially control freaks) is that imperfection is the real perfection.
Great Video Thank you
What I learned is when running astern the pivot point is approximately on ¼ from the stern, not ⅓ caused by the shape of the ship's hull under the waterline.
yes, it depends on the ship's block coefficient. a boxier ship like a tanker or bulk carrier will have its pivot point in a different position then a ship with lower block coefficient
What a great theory! Never been aware of this. Thank you sir!
0:12 I knew from the animation that the answer was going to be pivot point
maneuvering videos are interesting
If you run out of ideas for videos, perhaps you could explain the roles/motions of the four tugs that took USS New Jersey from her position in Camden, NJ, to Philadelphia for drydocking earlier this year? I watched the livestream and it wasn't always clear what they were doing and why.
There is also the rotational effect of the propellor. if you anchor or tether the bow you can use the propellor to turn
Ok, it's late and I am not entirely sober, but this one went a little too fast for me. I feel pivot point theory deserves an entire 10 minute video of it's own.
Like at 2:26 "But the ship's hull is also going to induce movement in water that surrounds it, as soon as we add in the forward motion of the ship..."
What forward motion of the ship? We were talking about moving a roughly bar-shaped object sideways through a fluid while pushing at the center. Why would it move forward?
Sure, there's a lot of complicated fluid dynamics, but to the experienced tug operator, it's all done by feel and instinct. Still hard to beat that!
Very nice video, learned a lot!
One day, probably not soon, maybe not ever, but one day, the knowledge from this video will come in handy. As I am applauded for single-handedly saving thousands of lives by instructing something to push something else a little bit in front of its centre of mass.
On that day, I’ll be asked why the hell do I know that. And I will not remember
All manoeuvres need to be preceded by the statement;
“Hold my beer, I got this”! 😇😂
I don't understand the section at 2:26. Why does the hull induce this kind of movement?
I'd love to see a pilot/tug captain simulator, where we could put all these tutorials to use
So that's why I was having problems docking at the Space Port. 😋
the art comes in thinking 3 steps ahead of all this.
Great video!
right hand rule appears in so many interesting places
Ah! I understand it all now. I understand that I don't understand it at all.
0:20 man, i haven't played Ports of Call in years
well, there's also tug push point marked by ship builder which position not ideal at all for efficient maneuvering.
instead of reinforcing efficient pushing point, builder just marks frame parts for tug to push which way far from ideal pushing point.
Dr. Ross Geller approves of all pivots.
I don't understand.
The title says "Why Don't Tugs Turn Ships?" implying that they don't do it.
The video however talks about how the thrust applied at different points of the ship affects the turning of a moving ship, and it is explained with both tugs and the ship's own thrusters.
So do they not use tugs (like the title suggest) or do they use tugs sometimes?
Will bow and stern shapes change where the pivot point is? I assume it would as water will move over the shaped area differently than it would a flat side, though I also assume it wouldn't have as big an impact as the ship's own movement
Thanks.
I would think that how far the pivot point migrates with ship motion would depend not only upon the direction of ship's motion, but also the speed.
That’s cool. Another cool fact, if you drive a forklift at your job, your really only a body of water away from driving a four winns motorboat (the driving controls are really similar, my dad had a four winns when I was a kid and I drive a forklift currently and the stirring and excellratir controls are extremely similar.).
Before watching this, it makes sense.
Is the animation at 3:46 backwards? Shouldn't the tug on the left have an easier time thus pushing the ship further off angle?
Bow and stern thrusters are not designed to work above about two or three mph, and you do not mention that pushing a stationary vessel in the centre will also induce a turn as there will inevitably be differing currents fore and aft creating a difference in resistance,.
So if a ship had bow and stern thrusters could they fire them in opposing directions and flip the whole vessel around its center point? at least if it was sitting still. I think I start to realize that picturing how ships on water work is more complex at times than ones in space.
The motion of the ocean really does matter
…as does the angle of the dangle.
so..... when moving forward its more efficient to use aft thrusters then bow thrusters, right? (of course if your ship have aft thrusters)
2:00 - this is incorrect. The imaginary pivot point moving in reverse direction - FROM the tug. At 2:10, when the ships has almost no angular speed, the imaginary pivot point is at infinite distance. More simple - there simply cannot be a center of rotation/pivot point around which nothing rotates :)
In the case discussed in the video, the ship can turn right when pushing it near the center of its mass for two reason:
- it is not the center of mass
- sum of all moments of forces around the center of mass is not zero. It may not be equal to zero because the force of water pressure along the hull is not constant - see Bernoulli effect for example.
It is for the reason that the force applied to the center of masses does not cause rotation that the sailing mast, if it is one on sailing ships, is set above the center of masses - or, in the case of several masts, is calculated so that the sum of the moments is zero.
How does the uneven weight distribution/centre of mass affect this?
So, you're telling me the answer is, "hull shape"?
It's always hull shape, isn't it?
so would this physics be the same if the tug was pulling on the end.
"But, it has to beight against the risk of overcomplication, when an easier solution will suffice."
Physiks my friends!
This is physiks xD
I don't like this explaination. What if the ship is moving very slowly, then the pivot has to be near the center. At which speed does the pivot meaningfully shift towards near the 1/3rd mark? Surely it must shift continuously as speed increases.
It sounds like some parameters are missing from the explaination
What I've learned in the academy - is that when you run propellers astern/ahead the pivot point strikes the point in the hull where it meets the water, since at that point the water is like a "wall".after the ship starts moving - the pivot point settles about a 1/3rd from the stern/bow. the exact position is determined by the ships block coefficient. boxier ships have a tighter turning radius while more fine shaped ships have a bigger turning radius.
So then when moving forward why not push from the the side closest to the stern hmm?
Why do they still call it a tug when it's pushing? Shouldn't it turn into a shunt?
That’s interesting how bow thrusters are largely ineffective while a ship is at speed. I guess that answers the hypothetical “what if” question regarding how history might’ve been different if the RMS Titanic had been equipped with them. The most likely answer being, “It wouldn’t be”. The crew of that beautiful broad would’ve slammed her into the wall of ice just the same.
If the on-again/off-again 'Titanic II' project ever does actually come to fruition, I noticed that the concept art portrays her as being equipped with bow thrusters this time around. But regardless, I should think the ‘speeding through an ice-field’ lesson has been well good and learned for all coming time, and utterly ingrained in seamanship the world over. But always beware, and woe unto any who say, “It can’t happen here”, or “It can’t happen again”.🫤
It would be more effective to add stern thrusters if the ship has standard shaft drive. The Titanic, with stern thrusters, could have turned much more rapidly than with bow thrusters. A lot of cruise ships are being built with podded propellers, which makes the main engines do double duty as stern thrusters. pod drive have the propeller in front of the pod, so they point to the right to turn left.
Amen.❤.
@@jaquigreenlees wouldn't matter, bow/stern thrusters are useless above around 3 knots
I had an problem like this in high school physics. I still have no clue how to solve it.
I need a Ship Piloting Simulator game on Steam.
why the heck is this interesting? i'm never gonna drive a ship...
Why is the video called "Why Don't Tugs Turn Ships?" ? That topic didn't seem to come up at all, the video was about the counterintuitive way that a tug pushing in the middle would cause a moving ship to turn...
So I just watched the video, tugs do turn ships then?
And when you throw in the shape of the tugs employed and the speed of the ship, you have yet another variable.
A deep draught tug pushing on the bow of a forward moving ship creates a low pressure area alongside the tug on the side away from the ships direction. With enough forward velocity, most of the tugs power is committed to maintaining its position alongside and the low pressure will overwhelm the tugs actual force on the ship causing the ship to turn into the tug.
Its complicated and not always intuitive and that's why there is always an apprenticeship program for piloting. There is some stuff you just have to experience before it either makes sense or becomes intuitively predictable.
Now my head hurts
👍👍👍
I understood "lever"...
Uhm tugs do help cargo ships turn around. I was actually part of that job. Been a lineman for two years.
Did you just say that a vector generates a force? Tf does that mean?
Last?
you should have explained the ship specific terms before you used them, because you got me lost.
Well why didn't you just say it moves about the center of inertia!
But what about the drag from the massive balls of the pilot hanging in the water 🤷♂️
PIVOT!
2 points. 1) Tugs do turn ships…regularly. 2) Your suggestion a tug pushing at the apparent centre of a ship results in the stern being pushed farther than the bow is the opposite of what actually happens. The rudder and screws result in (what you call a pivot point) being nearer the stern than the bow.
Physics!
1) we know this simplified version works, so lets use that
2) so thats why it works that way!
3) keeps using the simplified version cause it still works, but now knowing why it works.
4) Profit?
Did anyone else think a USB device was connecting and disconnecting on your computer?
Wait, they don’t?
But the ship is not moving ahead at all !
Ehh, this stacks up to “consider a spherical cow”
👍🏻🇬🇧👀...
Noda 🤦 how do people not know this 🤷
0:22 UH ACTUALLY THATS JUST A THEORY SOOOOO 🤓🤓
The word 'theory' means 'factually proven' in a scientific context.
@@hotdogvan3399
the joke: --------------------->
your head: 🤓
@@snowcat9308 Sarcasm doesn't translate over comments. That's why we use the /s tag.
@@hotdogvan3399 Or emojis 🤓
There's a reason scientists aren't piloting ships though...
Where a scientist would bring up a calculator to make a turn, a skilled skipper would just make the turn intuitively.
Er... scientists have intuition too, you know.
@@beeble2003 Of course they do. But the sarcasm is still there and it went right over your head.
@@RealCadde Sarcasm is when you say the opposite of what you mean, to mock that position. So, if you're being sarcastic, you're mocking scientists for having excellent intuition. Why is that something that deserves mockery? You're just making no sense.
Close to 3 mins you lost me. I'm a naval architect. Did anyone understood this explanation?
Poles😮😮😮😮
Look at all these comments, its not Helpful 99% of the time.😊
Misleading title
Ok karen
what? that's exactly what he says in the video
@@3_14pie
I think interpretation is the issue here. The title can be interpreted as "Why tug boat CAN'T turn ships"
@@mediup2472how’re you supposed to read the title
oh I was about to comment the same thing but I think I figured it out!! I think it's actually a response to an observation - "I always see tugs pushing on the side of a ship near the front, but the ship doesn't turn. Why doesn't the ship turn when the tug pushes the front of the ship to the side?"
those of us who have never made that observation are left thinking "uh, that sure looks like they DO turn ships?"
2nd?
No.
101th comment
I'll just say that pivot point theory does not make it easier. Until you start talking about actual forces involved, it's just some meaningless words