Ships — Why Steel Floats and Why There Is a Bulb Under the Bow

Water pushes back as much as it is pushed

Step into a bath and the water rises and you feel lighter — the same event. Your body pushes water aside; the water wants its place back and lifts you, by exactly the weight of the water displaced. This is buoyancy.

A nail displaces little water, so the lift is little. A ship is hollow and displaces a great deal. If that water outweighs the ship, the ship floats.

It is hard to believe in words alone. In the board below, hollow out a steel box yourself and watch where it starts to float.

Tool The Buoyancy Board — Why Does a Lump of Iron Float? Pick the box's material, what fills it, and the liquid, then float it; load a ship with cargo and watch how far it sinks.

A ship does not cut water; it makes waves

What eats a moving ship's power? Friction with the water, and the pressure difference between bow and stern. And one thing that belongs to ships alone.

A ship leaves a wake. That wake is not free; every ripple is energy the ship paid for. The share climbs steeply with speed, until a large ship spends much of its power making waves. This is wave-making drag.

The striking part: the waves cannot be prevented. But they can be cancelled.

A little further in

Towed before it is launched

Finding out a ship has too much drag after building it is too late. So a small model is floated and towed first: in an indoor tank two hundred metres long, the model is pulled at a set speed and the backward force is measured.

There is a trap. Multiplying the model's drag up does not give the real ship's. Waves grow with size one way and friction another, so a method for separating the two and scaling each has been refined for over a century.

That long tank stands at the maritime research institute in Daejeon, beside a tank that makes waves to order, so a ship's motion in a typhoon can be tested indoors.

Where the sea itself is measured

Ships need the sea known: how deep, which way the water runs and when, how high the waves rise in a storm.

1. The ocean science institute (Busan) — currents, the deep sea, marine robots. Its platform on Ieodo rock watches the path typhoons take.
2. The hydrographic office (Busan) — the sea's maps. Depths are sounded into charts and tides forecast. The seabed around Dokdo was surveyed here.
3. The fisheries science institute (Busan) — counting what lives in the sea, and how much.
4. The polar institute (Incheon) — the frozen sea, from the nineteenth piece.

The sea covers seventy percent of the Earth, yet its depths are less known than the surface of the Moon. Satellites cannot see underwater; there is nothing for it but to go by ship and measure.

The next ship sails itself

Two big lines of research now: ships with no crew and ships with no oil. The first carries the robot problem of the tenth piece out to sea — spotting and avoiding other ships in waves and fog.

The second brings the hydrogen of the eleventh piece aboard. But ships are far heavier and go far further than cars, so batteries will not do; engines burning ammonia or hydrogen are being tested.

What you would study to do this

Korea is among the world's largest shipbuilders, so the field is wide.

1. Someone who shapes the hull — naval architecture, calculating how water flows.
2. Someone who builds and tows the models — tank testing, needing both hands to shape the model and instruments to read it.
3. Someone who measures the sea — oceanography, geophysics, months at a time aboard.
4. Someone who actually builds the ship — welding, pipework, electrics, painting. Most of a shipyard is these people.
5. Someone who sails it — deck and engine officers, trained at maritime universities and maritime high schools.
6. Someone who builds sea robots — mechanics, electronics, and communication underwater.

The fourth line is the unexpected and the widest. One ship has hundreds of thousands of welds. The fifth piece showed the hands that weld a rocket; a ship needs thousands of them — a direct road from technical high schools in Busan, Geoje and Ulsan, where the yards are.

The maritime high schools of the fifth line train people for work at sea from secondary school on. There are two, in Busan and Incheon.

The question that remainsIf the wave could not be removed but was erased with another wave — how should we approach the problems we cannot remove?