- All right, wish me luck.
I don't think it'll be long.
A while back I made a video
about how pop-pop boats work with a transparent one.
So many people commented
that it would be amazing to see a life-sized pop-pop boat.
And then brilliantly, a few months later I got an email
from Makar Parman at the Ahhaa Science Center in Estonia
saying, "Hey, we built a life-sized pop-pop boat.
Do you wanna come and have a play?"
Like of course I do, but first let's just rewind.
Like you can't go straight to a life-sized pop-pop boat.
It makes sense to scale up in stages
to see if the thing will work.
So first they built a teddy bear sized pop-pop boat
as a proof of concept.
Oh wow, okay.
So it's the, I mean, it's the same as the toy one,
but a bit bigger.
How'd you fill this thing?
(water bubbling)
Well, now I want a drill powered pump.
But I mean, so, but anyway,
so there'll be a pocket of air here,
but I guess that doesn't matter.
This is how we power it.
- So that's where it's gonna get heat from
and it's powered with a small propane tank.
- Okay.
I don't think I want that on though.
- Okay, sure.
- I think let's keep that off
'cause I want to see what the engine does.
I mean it's just like with the mini one,
you can slide that off, and that's more interesting to me
'cause you can see what's going on.
Can I set fire to it?
(fire roaring)
Holy cow, okay.
With the toy pop-pop boat,
you can see and hear the cycling of the engine
because that top plate pops up and down.
It's like a brr sound that you get.
With this, the top plate isn't popping up and down
so you can't straightaway see that it's working.
But down here,
you can actually feel the propulsion coming out.
It's like 1, 2, 3, and look, you can see it as well.
Can you see that?
5, 6, 7, 8.
(boat clanging) Oh my god.
Okay, so sometimes that does pop up and down
and it's quite surprising.
The water's warm, but it's not dangerously hot.
Despite being able to feel
a decent amount of propulsion from those pipes,
the progress of the boat is quite slow.
So this footage is sped up,
and of course there's no way to steer this thing,
so Makar jumped in the water at one point
to turn the boat around
so that it would actually make its way back to us.
Once they got the medium sized pop-pop boat working,
they felt confident that they could make one
big enough for a human to ride in.
Actually, they built the engine separately
and then attached it to a boat they already had.
What I love is it looks like a speedboat.
I bet it doesn't go like a speedboat.
It's a nice design
because you can just attach it to any boat, really.
This is the tubing for the propane.
So the gas tank will sit in the middle,
and it feeds the propane down through here,
around through here, and it splits into four burners.
So it splits there into two,
and then those two each split into two.
You've got four burners there.
This is thermal protection,
otherwise this tubing would melt.
This plate here is popping in and out.
I don't know if we'll get a similar thing with this.
If that thing's gonna pop up and down,
that's gonna be quite impressive and terrifying,
'cause I'm gonna be in the boat.
When you fill a pop-pop boat with water,
the way you do it is you just submerge it,
and because there's two pipes there,
air will flow out of one pipe
and water will flow in through the other,
so it's dead simple.
With this, it's not so easy
because you can't just dunk it in the water.
So with this one you can fill it with water from here.
That's what that's for.
But if you imagine doing that with this one,
if you fill this with water,
it's just gonna pour out of here.
So they've got valves at the back as well,
these things here.
So you close these off, fill it with water
you keep this open so that,
as you're filling it with water, the air can escape.
And then once you close both of those off,
you can then open the valves at the bottom,
at the end of the pipes underwater,
and it's not all gonna spill out.
I think that's how it works.
Do people agree? Good, I've got it.
I mean, to put it simply,
this boat was never meant to be paired up with this engine.
When you put the engine on the back,
it's so heavy the whole thing tilts up.
So we've got these floats attached to the engine
to give the engine some buoyancy
to try and match the buoyancy of the boat
so it doesn't all tip up.
Just now we've realized that one of the floats
on the left side, port side is taking on water.
So I'm glad they figured this out before I got in the boat.
The floats are right next to the heaters there.
So it looks as if maybe there was some heat deformation,
and then a crack formed, and that's how the water got in.
Do we have replacements?
- We're bringing them.
- So they already exist.
I mean, we're very much on the cutting edge
of life-size pop-pop boat technology
Ready?
(fire roaring)
- You can sit on the red part,
I think it would balance it out better, that's possible.
And then you can take the gas tank basically the seats,
you insert it.
- [Steve] I'm using AI here to enhance the speech
because the boat was so noisy.
It sounds weird in places, but trust me,
it's better than the alternative.
That bit there was on fire when it shouldn't be,
they added some gaffer tape,
I dunno why. But that bit's no longer on fire.
So that's nice.
Do I feel safe?
Weirdly, I do, and it's probably misplaced.
The thing that scares me most
is the loud sound that it's making
because it's bending metal, you know,
and normally in an engine that's undesirable,
but in this engine it's expected behavior.
This is amazing.
So you can see the cycle happening
because this is going up and down very noisily.
It's interesting,
you can't really see the disturbance in the water.
And like, when it was first ignited,
there was a lot going on;
there was bubbles coming out. In the sort of steady state,
if you like, of engine operation,
it's just water being sucked in and out.
You don't see any air coming in and out.
I'm gonna angle this around like this.
I mean, it's amazing that I can steer this thing.
Very rare that a pop-pop boat can be steered.
It's really nice to see that metal plate coming up and down.
That's the frequency of the engine.
It's so much slower than the toy pop-pop boat,
which makes that sound (brrrr).
That's the frequency of the toy engine.
Though interestingly,
the fact that that metal plate can flex
makes the engine less efficient.
That's because the water inside that tank
is boiling into steam.
So you have this expansion of gas
that forces water out of the tubes at the back.
That's what provides propulsion.
But if the vessel can expand with the steam,
that reduces the amount of water being propelled
out the back of the boat. But it's kind of reassuring,
and it's the same thing that the toy pop-pop boat does.
It's what makes the pop-pop boat so loud.
This is about the same speed as a toy pop-pop boat,
only it's massive.
That's really interesting actually, isn't it?
Why does the speed of the larger boat not scale up?
Like this boat is about 20 times longer than the toy boat,
but it's not 20 times faster.
It's no faster at all, in fact.
I think that's because of something
called the square cube law.
The square cube law relates to what happens
when you scale things up,
like what happens when you take an object
and double it in size.
Like this cube is double the length of this cube,
but it's also double the width and double the height.
So what happens to the volume?
Well, this cube has a volume
of one times one times one equals one.
This cube on the other hand has a volume
of two times two times two, which is eight,
so the volume has gone up by a factor of eight.
What about the surface area?
Well, looking at just one of the faces,
we can see that the surface area here is one times one,
which is one.
Multiply that by six
to get the total surface area of the cube
because there are six faces.
Whereas the surface area of one of the faces on this cube
is two times two, which is four.
You can multiply that by six as well
to get the total surface area of 24.
So that means the surface area went up by a factor of four
whilst the volume went up by a factor of eight.
So counterintuitively,
the volume and the surface area scale up at different rates.
I remember when my physics teacher first showed me that,
I was really surprised because it went against my intuition.
I just thought everything would scale up at the same rate.
So to really hammer the point home,
if I've got this one cube here
and I want to multiply the volume that I have by eight,
then I can just grab seven more cubes.
Look, now I have eight times the volume.
And because I have eight cubes,
I must have eight times the surface area as well.
But look what happens when I stack these eight cubes
into one single larger cube.
Look, I'm losing all this surface area
that's now on the inside.
So you can really see how the ratio of surface area
to volume goes down as you scale things up.
I could talk about the square cube law all day,
but instead I'll link to some good videos
on the subject in the description for those interested.
But the square cube law is important to the pop-pop boat
for lots of reasons.
Like when you scale up a pop-pop boat,
the volume of the tank goes up
by the cube of the scaling factor,
but the surface area of the tank goes up by the square.
That's important because the speed
with which you can heat the water in the tank
is limited by the surface area you have to apply heat to.
Similarly, the cross-sectional area of the pipes
that provide propulsion for the boat
goes up by the square as well,
but the mass of the boat goes up by the cube.
So the boat becomes harder to push
more quickly than the engine's ability to push it.
It'll be almost impossible to factor everything in,
especially as some aspects of the boat don't scale exactly.
But it is interesting to note that when it all shakes out,
the speed of the boat
seems to be about the same as the toy one.
The other thing that's interesting to think about
as you scale up is the frequency of the engine.
Like how many cycles are there per second or per minute?
Really, you've got a simple harmonic oscillator here.
You've got a mass, which is the water inside the pipes
pushing and pulling on an elastic medium,
the elastic medium being the springy gas inside the tank,
just like the springy gas inside this syringe
leads to simple harmonic motion.
So you can model that like a mass on a spring.
As we scale up the boat,
we're increasing the mass of the water inside,
and when you increase the mass on the spring,
you'll find that it slows down.
Also the springiness of the gas in the tank,
that's gonna be related to the volume as well.
As you increase the volume of gas,
that's like decreasing the stiffness of the spring,
which will slow down the oscillations even more,
so it shouldn't be any surprise that the engine oscillates
much, much more slowly than the toy boat.
I suspect this boat has a bit of a bias.
Like if I held it straight like that,
it would probably go that way.
And by steering it like this,
I'm essentially getting it to go in a straight line,
which means I may never return.
I don't think we need two pipes,
like I don't think any pop-pop boat needs two pipes.
It should just work with one according to the theory.
With the toy pop-pop boat, it's useful to have two
because you squirt water through one
and the air comes out the other.
With this, because of the way we fill it,
we could just do it with one pipe,
though I think to get this to work
as efficiently as possible,
we want to maximize the surface area
of the pipe that's under the water,
because the pipe that's under water
is the thing that does the cooling of the steam.
So to be clear, this is completely full of steam now
all the way down to where the pipe touches the water.
So the level of the water is going up and down,
oscillating around the water level of the lake.
When it dips below the water level,
the steam that's now under water
is being cooled by the surrounding pipe
that's submerged in water, so it rises back up.
So it's going up and down in that way.
So I think if you had several thinner pipes,
you'd have a greater surface area,
maybe this thing would work a bit better.
Yeah, I don't think
I'm gonna be able to chart a course back.
Interestingly, the tanker stopped breathing.
Well, no, it is going up and down, but not as much.
There was a loud sound, a big judder in the boat,
the whole boat kind of juddered.
I think I need rescuing.
Are you rescuing me or are they sending the big boat?
(Steve chuckling)
See, now we're moving.
It's almost as if there's a better design of engine.
By the way,
the Ahhaa Science center has some amazing exhibits.
It's all hands-on stuff that you can actually play with,
so if you're in the area,
I strongly recommend you check it out.
The thing that I love most about YouTube
is I can make videos
about the things that I think are interesting,
and eventually the people
who also think those things are interesting
will find my videos.
That's very different to the way it works on TV,
and it means that the viewers of my videos
have become a kind of community of people
who are curious about the world.
They love solving puzzles and figuring out how things work,
so I already know that that's what you're like.
But if you are also currently pursuing
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