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How does a boat float?

Okay, normally we like to blog ‘How to’ articles to help boost your sailing or fishing prowess. But while sitting around thinking about boats (which we do a lot), it dawned on us that we’ve never answered the biggest most obvious question of them all.

How. Do. They. Float?

Seriously. How?

The science of floating was initially studied by Archimedes (you’ve probably heard of him!). He’s a somewhat famous Ancient Greek scientist who worked out that if you place an object in water, it will push enough water away to make space for it.

What he worked out was ‘displacement’.

Displacement happens when you get in a bath and the water makes way for you. It happens when you place a rock in a cup of liquid, and the liquid rises to make room for the rock.

Displacement is actually pretty cool, and it happens all the time.

Why does displacement matter?

When something enters water, there are two forces, which both act on it.

  1. Gravity – a downward force.
  2. Buoyancy – an upward force.

Gravity is determined by the weight of the object (let’s use the rock as an example). Buoyancy is determined by the weight of the liquid, which is displaced by the rock.

Now let’s put this all together…

An object floats if the downward force (gravity) is less than the upward force (buoyancy). In non-science speak, if an object weighs less than the volume of water it displaces, it floats.

This explains why a boat floats but a rock doesn’t. The rock is heavier, and displaces only a small amount of water. As a result, it sinks, since its weight is greater than the water it displaces.

Back to boats

A large boat floats, because even though it may weigh a lot, it displaces a huge volume of water, which weighs much more.

On top of this, boats are specifically designed to displace the right amount of water, in order for them to easily float.

There is a heap of complex design that goes into developing a boat (and we’re glad there are brainiacs who can make this happen).
We’re also glad Archimedes worked out displacement theory, so we can better understand our favourite pastime.

Love your boat?

We insure large and small boats, as well as jet skis, kayaks, SUPs and other vessels, so you can worry about enjoying your time on the water.

Contact us for an obligation free quote, and happy floating!