I understand that a boat floats because of the shape of it, and how it comes to a point at the bottom. But I still don’t get how such a HEAVY AND LARGE peice of METAL can float ontop of the water…
What if you carved a large rock into the shape of a canoe, it wouldn’t float would it?
Someone care to explain exactly how a boat does float?
A boat will float when weight of the water it displaces is greater than the weight of the boat itself.
A metal boat is indeed heavy, but water is also very heavy.
In fact it would, as evidenced by the concrete canoe, a staple of engineering design competitions.
Well, concrete does, so you should be able to do it with stone, too.
The shape doesn’t have anything to do with it. As tastycorn said, its all about displacement. A boat may be made out of metal, but most of its volume is the air in between the metal parts. As long as the metal and air weighs less than the water, it will float. A large rock shaped like a canoe would likely also float. A rock shaped like a pie pan would also float, assuming that the walls were high enough to trap enough air inside to make the whole thing weigh less than water for the amount of volume it displaces.
A solid block of rock in the shape of a canoe would sink. However, if it had enough air space, it could work. The trick, as tastycorn mentioned, is water displacement–if the weight of the water displaced is higher than the weight of the object, the object floats. There’s even an anual competition in which engineers build canoes out of concrete (see this web page: http://concretecanoe.org/ ; I don’t know details, I just remember hearing about it when I went to Michigan Tech).
Great minds think alike, micco 
Something else interesting. Many people assume that you need a large body of water for a boat to float. In actuality, all you need is just enough water for the boat to clear the container.
Imagine a boat sitting in a pool. The pool almost exactly the same size and shape of the boat, but just a tad larger. With the right tolerances, you could have an aircraft float in 20 gallons of water.
Uhhh, aircraft carrier, I mean.:smack:
hmm, interesting… wonder if that has ever been done? Or something similar…
Now thats somethign I want to see before I die… an aircraft carrier floating in 20 gallons of water 
You can see the principle at work yourself.
Get two identical “stackable” glasses. Fill one with water, and place the second one inside the first. Watch it float, then remove from the water and see how much is left in the glass.
Can anyone explain what the actual mechanics of flotation are? I understand Archimedes’s principle, and upthrust/boyancy - but what is happening at an atomic level?
At an atomic level? Nothing special. There’s no atomic interaction going on, other than the standard electrostatic repulsion (the same thing that happens whenever you, for example, touch something), and perhaps graviton emission/absorption, if gravitons actually exist (the jury’s still out, as far as I know).
Surely every macroscopic physical phenomenon should be explainable at the atomic level, including flotation? If it’s just random jiggling of atoms, why is the macroscopic law so precise? (I believe it’s something like, a body floats in a fluid if the weight of the fluid displaced is greater than the weight of the body)
Ah, took me a minute to figure this out. I thought “how could it float in 20 gallons of water? It would displace the 20 gallons immediately and hit the bottom.” But then I realized you were talking about the remaining water after it displaced the initial thousands of gallons.
Actually, you never need the initial 4 trillion (or whatever) gallons in the first place, provided you already know how much water will be needed to fill the gap between boat and pool, up to the waterline.
It does help to think about it starting with a full pool though.
This quote comes from a concurrent locked thread asking “How much water is required to float a boat” That thread was locked due to the presence of this thread.
Now most of us are aware of the factors of bouyancy and surface area doesn’r apply.
I was going to rip him apart because he hasn’t owned up to a previous grevious error, but he is actually right in this case, although I nearly missed the context in which his assertion can be demonstrated.
In the fiberglass boat industry, hulls are commonly floated out of molds initially to break the adhesion. It takes very, very little water.
If there isn’t more mass of water available than mass of ship, it ain’t gonna float.
Nope. It’ll float, all right.
The key is that you have to have a container holding the water which is strong enough to withstand the pressure. The boat pushes the water to the sides, and in an ocean that water would be pushed back by all the other trillions of gallions of water out there. With a pool the sides of the pool need to be strong enough to hold back the water pushing on them, otherwise the pool would break, the carrier would be lying on its side, and the backyard would be flooded.