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Science Out Loud.

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So if I take this box and just
obliterate it in the corner

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right here and then
put it in the water,

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the weight of the water rushing
in will cause the box to sink.

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If I take this box
and do the same thing,

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it tips over a little
bit, but it still floats.

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This box uses the
same kind of design

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that naval architects use
to prevent ships 1,000

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times bigger from sinking.

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What's so special
about this box that

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prevents it from sinking, even
with the big hole in its side?

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Let's talk about why ships
sink in the first place.

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You probably know
that things will

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float in water if they're
less dense than water

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and sink if they're more dense.

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The metal that this
ship is made out of

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is way more dense than water, so
you might think it would sink.

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But that metal is
shaped so that it

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traps a lot of air, which
is less dense than water,

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inside it.

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So the average density
of the hull of the ship

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is actually much lower than that
of water, so the ship floats.

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But if the hull springs a
leak and fills up with water,

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there's no more air to lower
the average density of the hull,

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so the ship sinks.

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The design of this box basically
prevents too much water

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from getting into it.

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This box's hull was divided up
into watertight compartments

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with these walls
called bulkheads.

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So when I made a
hole right here,

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only this compartment
filled up with water.

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The rest stayed dry and were
able to keep the box afloat.

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This box is subdivided,
and so is this ship.

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Say this ship is divided into
ten watertight compartments.

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If one area of this
ship got damaged,

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only that compartment
would flood, but not any

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of the others.

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The added weight
of the water here

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would cause the ship
to tip over a little,

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to be angled or
trimmed in the water,

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but it wouldn't completely
sink, and could still

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be taken to a port for repairs.

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So even with subdivision,
why do ships still sink?

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Well, it's impractical
and expensive

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to design an unsinkable
ship, especially

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because most of the
time, ships just

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don't see that much damage.

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What naval architects
do now is try

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to predict what kind of damage
is most likely to happen

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when designing a ship.

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Now, ships are more
complicated than this box.

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Naval architects have
to think about where

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to subdivide the ship,
the shape of the hull,

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and equipment that goes
into the compartments.

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We don't know when people
first start subdividing ships,

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but the caps of
Chinese trade ships

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as far back as the
fifth century indicate

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that water would be
able to enter the vessel

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without causing it to sink.

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It's pretty crazy that
technology that existed so long

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ago is still being used today.

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Hello, I'm Paul.

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Thank you for watching
Science Out Loud.

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For more information,
please visit our website.

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[LAUGHTER]

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See what they had me do?

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