Why Are Ships Not Sinking In The Water?

When you throw a small metallic pen in the water, it will sink, yet a big ship or boat sails in water and floats.  Why?  This is the question that all of us who have seen ships, ask ourselves and desire to understand the science behind it.

No doubt there is some mechanism behind all these ‘supernatural’ ships that seem to defy the forces of gravity.  Let us look at some factors that contribute to the floating of the ships.

Firstly, the weight of the ship determines the buoyancy.  This weight taken into account is both loaded and unloaded.

Secondly there is the shape of the ship to consider.  The weight of the loaded ships is calculated and compared to the weight of the water that is displaced once the ship is on the water. This is done by the designers of the ship.

Ships are not build as solid blocks of steel, on the other hand, they are hollow.  Therefore, because the ship occupies more volume, it displaces more water than its mass, thus its density becoming much lower and this aids it in floating.

The material that makes ship, steel, is denser than water and if the ship was just one big block of steel, it would not float at all, but because it is a big hollow box of steel, its density is less than that of water.

A needle or nail for example displaces very little amount of water therefore the weight of the displaced water is less than the weight of the nail.  On the other hand, the amount of water displaced by the ship once it is on water, is massive and is equal to its weight.  Because the weight of the displaced water is equal to the weight of the ship, then it floats buoyantly.

Think of a large container that has very thin walls and relatively strength members, which is designed to hold air.  Though it may contain many other things, the biggest capacity is occupied by air, it will float.

Ships are like this big container, full of other things but mostly air, made of steel material to hold the air.  The Archimedes principle supports this in that things full of air always tend to float.


We have seen that huge steel ships float because they displace an amount of water equal to its weight.  Ships are hollow steel containers full of air and cannot sink as compared to a box of steel that just sinks without effort.

Ships are able to navigate on oceans and fresh water because they are like big containers with strong walls but full of air.  A nail or needle displaces very little amounts of water, therefore it becomes heavier than the water displaced.  This causes it to float.

Next time you see that ship, know that there is an explanation to the ‘supernatural’ floating of the steel metal container.

In simple terms, if the volume of an object is less than the volume of water displaced, the object will float.

Written by Anne Mwangi