Sounds like a kid's question? Something like, "Why's the sky blue?" WARNING: Try to answer either question and you might get stumped!

Well, don't laugh but even if you do an internet search, you'll get the wrong answers! You'll be reading about the ancient mathematician Archemedis who discovered displacement. He proved that floating objects displace (replace) an equal amount of water to the volume of the hull below the waterline and an equal amount of weight as the object that's displacing it. Then volume times weight of a cubic foot of salt water (64#) equals weight of water displaced which is equal to displacement (weight of boat).

The science of naval architecture is based on this important law. But it does not explain WHY boats float, large or small. After your internet search you will still be wondering why boats float.

Google 'why does a boat float?' and read about the ancient mathematician and displacement. That may be somewhat related to the question at hand but it doesn't really answer it. And we thought that the place for accurate information was the internet!

The real reason why boats float is that air is lighter (less dense) than water so if there's enough air inside the hull, the heavy steel or fiberglass object will float on the more dense water (than air). Air is what allows the ship to stay afloat.

The proof of the importance of air is evident when you see a hole made on the hull, water intrudes expelling air and the density of the ship becomes higher than the water's density and the boat will then sink.

Don't you feel like the cat that ate the canary knowing that you are one of the few that really understands this basic principle and how it's not considered in many other attempts that try to explain why a boat floats?


-- Charles Avalos, AMS

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