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Why a Ship floats and a screw Sinks in the Water

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Why a Ship floats and a screw Sinks in the Water

Why a Ship floats and a screw Sinks in the Water

Your answer to the question may be very simple.

Buoyancy or Simply Upthrust of Sea Water.

While that answer is correct.

there are more details to it than you may think.

A screw is very small,

in fact, tiny in comparison to a ship.

A ship weighs thousands of tonnes.

For example, the weight of our ship is close to 25000

Tonnes when empty and now when she is loaded,

her weight is almost 175000 tonnes and yet she is sailing

across the ocean as if everything is just nice and fine

and nothing Significant is going on.

Compare that weight to this small screw,

its weight is hardly a few grams

let alone a Kilogram.

Being so light and almost weightless.

throw this in the water and I can promise you that

it will sink in a blink of an eye.

Buoyancy or upthrust of water is always there

and it acts upon every weight that is either floating,

Submerged or even partially submerged in the water.

The weight of the object pushes the object into the water

and buoyancy tries to push it out.

It’s like a tug of war that goes on

between the weight of an object

and buoyancy of water

once that object is immersed in water.

The question that arises is.

this buoyancy is acting equally on a ship

and on this small screw.

and still, the ship keeps floating

while the crew would still Sink …

So definitely there is something more to the answer

than Just the buoyancy of water.

That is where another thing comes in

and that’s called DENSITY.

The density of anything is defined as weight per unit volume.

Or in normal Urdu ” the weight in kilograms of an object

that can fit inside an m3 of Volume” is called density.

Just like any other Object in the world, seawater has its
own density ..

Ranging anywhere from 1001 to 1025 kg / m3,

Fresh water on the other hand has a density of about 1000
kg/m3,

if you immerse anything that has a lesser density in this
water,

it will float on its top,

If the density of the object that is immersed is higher

in comparison to the density of water in which it is
immersed,

The thing will submerge and Sink.

The classical example is Oil and Honey.

put some oil in water and it will keep floating on top.

put some honey in the same Water and the honey would Sink.

== Density ==

You might be asking yourself then why does Human beings

Sink in the Water.

Human beings have an average density of 985 kg/m3,

That’s much lesser than the density of Fresh Water.

Technically Human beings Should always be able to float.

They Should not drown in the water .. at all.

That’s absolutely correct.

And yes, if you’re a swimmer and know how to swim,

you’d also be confident enough to let your body float.

And human beings – if they’re not wearing the type

of clothes that would absorb water,

by design, would in fact never drown in water

if they don’t TRY HARD to swim or FLOAT.

If they’d trust their density and let their body float.

they will float

Now comes the more complex question.

Steel that is mostly used on ships is far heavier

and denser than both – the fresh water and sea water.

 

Why a Ship floats and a screw Sinks in the Water

ALSO READ: MORE MARINE FACTS 

Why a Ship floats and a screw Sinks in the Water

Whether we consider seawater of Fresh Water ..

Yet once it’s given the shape of a Ship,

it starts floating,

how is this achieved without lowering the density of steel

and even after loading Thousands of Tonnes on top.

The answer lies in the clever design that makes it possible
..

To understand this, let’s consider a log of Wood,

It floats on top of the water,

But if you see closely, very closely,

these logs are partially submerged ..

Slowly people understood one thing that

if by any means they make the log hollow,

some of the submerged portion of this log

will come out of the water ..

Now when this log is hollowed and launched again ..

Not only did the submerged portion reduce, but

You could fill up the hollowed portion with practically
anything

as long as it doesn’t submerge the whole wooden log

Now this wooden log was able to not only just float ..

but carry our stuff too..

Here – the density of wood didn’t change at all –

but by making the log hollow we were able to enable this log

actually, carry something for us and yet Float ..

What we did here is we changed the weight of the log

by making it hollow ..

Using the same principle people were able to carve out

bigger boats with wooden hulls enabling them

to carry not just goods but people and equipment too ..

Density wasn’t changed but giving them an elongated shape

with curved Shell, gives a simulation of lesser density

You feel that it’s less dense as the inside of a hull is empty

that in turn enables a boat to float.

Using the same principle engineers were able to figure out

that even if a heavier steel hull was carved out ..

as long as this hull was long enough and high enough –

Even after partially submerged in water – it will float.

It should long as this hull was long enough to float ..

& High enough to not submerge fully in the water ..

This steel-made hull would in fact float easily.

If you have a closer look at all steel made ships,

their some portion is always underwater,

This underwater portion of a ship increases when cargo is
loaded

and decreases when a ship is empty,

but a certain portion of a ship is always underwater –

and we call it Draft of a ship.

we measure this portion in Meters and centimeters,

Hence using a clever design,

and by using the dense steel metal plates

to build strong Ships,

we are now able to take advantage of water’s upthrust

and hence enable a ship to float.

Humans were able to Build a Ship

Trust me if you’d design this screw clever enough,

it will float too,

but that’s not how design and innovation works ..

To make floatable screws

we first have to have a real need

and then some proper usage of the floating screws

There should be a place where we can use them

Only then we will be justified to dedicate our resources ..

& money for the development of the screws

that can float on water.

Until then, any screw threw in the water

will keep on sinking

and every Ship will keep on floating.

I seriously hope that I was able to

convey some sort of information ABOUT Why a Ship floats and a screw Sinks in the Water

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Dr. Ajay Kumar Lal DG Shipping Approved Doctor

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