The Assassin (Sha ren zhe Tang Zhan)

Today on "Impossible engineering",

the kings of the sea.

On top of the ocean, the largest cruise ship in the world.

Nothing comes even close in terms of size.

And underneath, one of the most advanced submarines ever built.

The Virginia class is the stealthiest submarine

that the U.S. Navy has ever produced.

It took revolutionary engineering...

to make the impossible possible.

captions paid for by discovery communications

Royal Caribbean's Oasis class cruise ships

are truly kings of the sea.

Since 2009, they've held the title

as the largest class of passenger ships on the planet.

And today, a third Oasis-class vessel is under construction,

the biggest one yet...

longer, wider, and heavier

than any other that's come before it.

Sitting next to her makes me feel like

standing next to the skyscraper.

When it's finished,

the Harmony of the seas will be almost 8 times longer

than the statue of Liberty is high

and 2 times heavier

than the world's largest aircraft carrier.

Built with steel,

this king of the sea would be impossible

without some guidance from the engineers of the past.

For centuries, steelmaking

was an incredibly difficult and lengthy process

until the 1800s,

when inventor Henry Bessemer came up with a solution.

Traditionally, the wrought iron

was layered with charcoal and heated over days.

And the charcoal would diffuse into the iron,

and that would produce the steel qualities.

Very complex and difficult to achieve

and, therefore, very expensive, historically.

So, Bessemer developed an ingenious way

to mass produce steel.

And this is it... The Bessemer converter.

The converter's capacity is impressive,

but its real ingenuity is in how fast it creates steel.

Bessemer discovered that pumping air into iron

accelerates combustion,

increasing carbon reduction and burning off impurities,

resulting in quality steel in a fraction of the time.

To show how oxygen injection

really increases the combustion process,

I've got a simple demonstration here.

I've got a tray of charcoal.

With my thermal camera,

I can see the temperature of these coals at the moment

is around about 450° c.

So, now what I'm gonna do is start to blow pure oxygen

onto these coals and see the effect.

Wow. Look at that.

The impact is amazingly impressive.

Ah!

So, if I now look at the temperature,

it's gone up to 1,000° c, a hugely dramatic increase

in the temperature of these coals.

So Bessemer had found a really amazing process

to reduce the carbon in steel.

Mass production of steel took off,

and its elasticity and strength made it a hot commodity

for both railroad- and shipbuilders.

The Harmony of the seas

needs a staggering amount of steel.

Massive steel sheets are delivered

to the assembly plant by train.

Automated systems cut the sheets

into thousands of individual components.

The steel panels, girders, and smaller components

are welded into modular sections called blocks.

Individual sections are joined together,

forming what are called grand blocks.

Made of steel, there are 90 grand blocks

on the Harmony of the seas.

A custom-built gantry crane

lifts each grand block into the dry dock.

The 90 blocks come together

to form the world's largest passenger ship.

Sitting as tall as tower bridge,

it's as long as five jumbo jets and as wide as a soccer field.

When I really look at her, I'm amazed, always,

always, every single time, by the size of the ship.

It's big, but it's beautiful. It's awesome.

You can definitely call this ship a small city.

It can house almost 9,000 passengers and crew onboard.

But how does such a gargantuan structure

move across the open ocean?

The engines are the heart of the ship

and provide the power forward to the ship.

Without the engine, a ship is not alive.

Powering this king of the sea would be impossible

without help from one of history's great innovators...

and that innovator was Rudolf Diesel.

This is the hc oersted power station in Copenhagen.

And, inside, you'll find a giant version

of Mr. Diesel's early engine concept,

which changed the face of the industry globally.

When it first powered up in 1933,

the Diesel-powered hc oersted

was the largest engine of its kind.

It's 40 feet tall and weighs 1,400 tons.

Back in the day, it could produce

a mind-blowing 15 megawatts of power.

It's absolutely huge.

The real power of this engineering colossus

comes from Rudolph Diesel's brilliant design,

patented in 1894.

This is a fire piston,

and this little piece of kit was what inspired Rudolph Diesel

in his development of the Diesel engine.

And it works like this.

You have a small cylinder where you add a bit of cotton wool.

The cotton wool will work as fuel.

You have a little piston.

When you push down the piston here,

the air will be compressed, the temperature will increase,

and it will finally ignite the cotton wool.

And it goes something like this.

Compressing the air created heat,

the heat forced the cotton wool to burn, turning it into energy,

which forced the piston back up again.

The perpetual motion

within the compression ignition engine

works almost exactly the same way.

Air is drawn into the piston

and rapidly compressed, creating heat.

High-energy Diesel fuel is then added, causing combustion.

This pushes the piston out,

to start the process all over again.

I would say, within mechanical engineering,

it's the most important leap.

No doubt of that.

The hc oersted may have been a monster in its day,

but the Harmony of the seas's engines

are 6 times more powerful.

This is one of the most exciting days of the project.

Yo, Eivel, let's start her up.

But for the ship to be seaworthy,

it has to deliver beneath the waves, too.

So there are a few factors that are very important

for the fuel efficiency on the ship.

And, clearly, the biggest one is the hull shape.

The hull shape needs to be extremely well-designed

so that you have a good hydrodynamic shape.

So how do you design the perfect hull shape

for the largest passenger ship in the world?

The Harmony of the seas

is the largest cruise ship in the world.

Designing the perfect hull shape for this king of the sea

would be impossible had it not been

for an innovative breakthrough made over 150 years ago.

For centuries, shipbuilders had a kind of

one-size-fits-all notion about ship hulls.

There was one generic shape

that was considered the most efficient.

But there was no real way of testing this,

of working out how much drag, how much resistance

a hull would encounter as it moved through the water.

But in 1870, engineer William Froude

built a groundbreaking hydrodynamic testing facility.

And he used it to test differently shaped hull models

and drag them through the water on a steam-driven pulley.

We've got three different-shaped hulls...

A flat-faced square box,

a slightly streamlined rubber duck,

and then this sleek speedboat.

Like Froude's experiments,

Andrew makes sure each object is equally weighted

and tows the objects with a rope attached to a scale,

measuring the amount of hydrodynamic drag.

You can see this isn't slicing through the water.

It's sort of making a lot of turbulence.

If you look at the scales, 3, maybe even 4 kilos.

That's a lot of drag, a lot of resistance.

Next up, a slightly more streamlined rubber duck.

Well, that feels much lighter, and the scales bear that out...

Maybe 1.5, 2 kilos of force there.

And you can see the pool... Much less disturbed.

There are far fewer of those Eddies.

The duck's just skimming across the top of the water.

But I still think we can do better.

Let's try the powerboat.

This is almost effortless, maybe 600 or 700 grams, tops.

You can see much, much less disturbance to the water.

The pool's almost still, and even from this scale model,

you can see why we make boats in this streamline shape.

The key to Froude's discovery

lies in a model's wake pattern.

Froude's real Eureka moment was when he realized

that he could use a lure to relate the drag

on a scale model of a boat to one that was full-size.

Froude developed a formula,

now known as the Froude number.

That Froude number can then be used

to compare a model ship to a full-size one.