As a child, probably ever single human being made those tiny paper boats and made turned those rainy days into special memories. That little boat was based on the same principles that work behind the biggest ships on the planet. For many, floating metal giants like the ships and ocean liners of our world are an incredible feat. However, the principle behind these is something that was explained many years ago, at a time when science was in its early years.

The concept of floating was first explained to the world by Archimedes. The Greek physicist and scientist told the world how an object floated by displacing an equal amount of water in terms of weight. This concept came into the naval world and revolutionized boat design.

The Principle

The basic idea is that when an object is placed in water, it will sink only until the point where it has displaced an equivalent amount of water as its weight. That means, if you throw in a log of wood weighing 200 pounds, it will displace 200 pounds of water before it starts floating.

When applying the same concept to boats, all you need to keep in mind is that the boat’s shape needs to be such that before its entire weight in water is displaced. The reason you can get boats to float so easily is because they are full of air inside. The basic structure of the ship, inside, is made of rooms and halls, so what you get is a large iron boat that’s got air in these rooms and, as a result, the overall density of the ship is reduced.

Floating is nothing but a reaction of the water molecules to the pressure being placed on them. The pressure is not a pressure applied by the boat on the water – it is the pressure applied by the water on the boat, from underneath. The moment that upward-pointing force becomes equal to the weight of the boat on it, the boat will begin to float.

What you See

When you are on a ship, you see a massive ocean liner or a massive iron boat that weighs many tonnes and looks it. However, the average density of a boat is quite low. You see a whole lot of metal and iron and rooms with beds and tables in them – for the water, each and every element is taken separately. As a result, you see a lot more of the boat or the ship than the water has to match in weight.

The shape of the ship, with the hull shaped like an elongated bowl, is designed mainly to displace water. The wider the hull, the more water it displaces at one go. As a result, the heavier the ship or the bigger the ship, the wider it will need to be. You cannot keep building a ship higher and higher because that will simply sink down further than you want it to.

To know how do iron ships float, you need to know the principles of floatation and since the time of Archimedes, physicists have concurred that these concepts are the right reasons for any object to float on the surface of the water. So the next time you are travelling on a boat or simply going swimming, just remember that Archimedes’ principles will help you stay afloat because that is the natural way of the world.

George Staton – author

In his 30-years in the metal industry, George followed the constant innovation of firms like Midway Metals, that were on the cutting edge of technology. They helped ship building organizations with their projects and products that George himself has worked on have become part of many ocean liners. Today, George spends a lot of time as a consultant but also spends time in children’s schools, explaining various concepts of machining as well as answering questions like how is stainless steel made or how do iron ships float.