What keeps a Ship Afloat

Why don’t ships sink? When things are put into water they make room for themselves by pushing it aside. You push water aside when you get into a bath. That’s why you have to be careful not to overfill it. Although ships are heavy, they are hollow with high sides. This means they can settle quite low in the water, pushing a lot of it aside. This is also termed buoyant; the displacement of the water and whether the object will float depends on the object’s density. In fact, a ship won’t sink unless it is overloaded and becomes heavier than the water it pushes aside. But are there any ships that fly?  Oh sure there are; It’s like riding on air. People ride on air every time they travel on a hovercraft.

The hovercraft was invented by Christopher Cockerel in 1959. He discovered that trapping a cushion of air beneath a boat lifts it up above the waves, allowing it to travel much faster.  Although the hovercraft travels across water, they don’t float in it like other ships. Instead, they hover just above the waves, held up by a cushion of air. Hovercrafts can travel over land as well as water. There is also the hydroplane which skims over the water almost as if it is flying. In 1977, Ken Warby roared to 556 kilometers an hour in his jet powered Spirit of Australia.

How do submarines sink you might say, aren’t they ships too? Submarines sink by making themselves too heavy to float. Water is let into special tanks to add weight. When it is time for the submarine to resurface, the water is pumped out. Going up, the air goes in and the water goes out. Going down, the air goes out and the water goes in. One of the earliest submarines was built by Dutchman Cornelius van Drebbel and tested in the 1620’s. Twelve oarsmen rowed a boat below the surface of the Thames River in England.

So, the next time you go for a cruise you will not need to wonder what keeps the ship afloat; and you can go the extra mile of painting “magic” eyes on the ship to watch over you at sea and bring you safely to harbor like the fishermen in Portugal did. When you hear engineers talk about how heavy a ship is, you will hear about displacement rather than weight. This is because in order to keep a ship from sinking, the ship has to displace its weight in water before it is submerged. Unfortunately, accidents do happen but, in order to prevent cruise ships from sinking should something penetrate the first two lines of defense, vertical watertight dividers known as bulkheads are installed throughout the interior of the hull. These dividers keep damaged ships afloat by containing incoming water into a compartment or compartments, thereby preventing the whole ship from flooding and keeping you safe.