How Does Steel Float?

We all know that boats float on water. It’s something we see every day and yet don’t really question why. But if you think about it, the entire proposition seems weird. Boats are made from heavy materials – primarily steel – that have no problem sinking to the bottom of the ocean by themselves. So why can a ship  made of steel float as easily as a duck but a tube of steel go down like the Titanic?

You are my density

It all comes down to the properties of density and displacement. Ancient Greek mathematician, engineer and inventor of the phrase “don’t go through my browser history” Archimedes discovered that objects put into fluid are pushed upwards at an equal force to the weight of the fluid that’s displaced by the object being inserted into the liquid. Or, to put it more simply, a boat that weighs 100 kilograms needs to push at least 100 kilograms of water out of its way in order to float.

That’s a pretty easy task, as it turns out, because of density. The composition of every boat from a one-person canoe to a massive freighter is mostly air and thus quite light compared to the weight of the water that is underneath it. Even the massive amounts of steel used in modern ship construction pale in comparison to how heavy a large volume of water is. Therefore not a lot of a boat has to actually be submerged in order for the whole thing is floating.

You float my boat

Water by itself doesn’t know that it needs to push a boat up to counter gravity. Instead, the physics of water pressure kick in. When an object is inserted into water, the liquid exerts water pressure onto the object. The math of this gets complex but what you need to know is that the further down into the ocean an object is pushed, the more the water pressure around the object is pushing it back up.

So, boat engineers use this fact to design boat hulls (the part that touches the water) that allow water pressure to be exerted smoothly along the surface. Thanks to smart steel cutting and metal shaping, we now have boats that counter water pressure forces to provide extra speed and smoother handling than previous generations of designs.

This is why a boat floats and a steel rod doesn’t. Steel rods are too dense by themselves and are too heavy for the forces of water pressure to carry them back up to the surface.

At ShapeCUT we love talking about the myriad uses of steel on land, sea and air. Talk to the ShapeCUT team today about how we can help your business continue smooth sailing.