What allows an object to float is the force of buoyancy, which has to do with the difference in density between the object and the water. For example, icebergs float on water because ice is less dense than water. The same is true for a boat: a boat floats on water because, overall, it is less dense than the water. This is because, even if the boat is made of metal (more dense than water), its shape means that air (much less dense than water) accounts for part of the boat's volume.

The volume of water that the boat (metal and air) displaces--meaning pushes aside because the water and the boat cannot be in the same space at the same time--has as much mass as the boat does. This is why the boat floats with some parts above the waterline, and some parts below it. The amount of water the boat displaces, has exactly as much mass as the whole boat, so that the upward buoyancy force (from the displacement of the water) equals the downward gravitational force (weight) on the boat. If you add mass to the boat, it will need to displace more water, meaning it will float lower. This is how a leaking boat can sink: water begins to replace the air inside the hull, increasing the overall density of the boat to exceed the density of water--and sink! A lighter boat needs to displace less water and it will float higher.

The material from which the boat is made affects its overall density because different materials have different densities. For a boat of the same total volume, a wooden boat would float higher in the water than a metal boat, because the metal weighs more (and is more dense) than the wood. A paper boat would float higher than either a metal boat or a wooden boat.

The material used to build a jon boat has no impact on the buoyancy of the boat.

" Boats float as a result of the displacement of water and not because the boat’s construction material is buoyant. So there is no such thing as ‘aluminum jon boats are more buoyant than either wood or fiberglass jon boats as some people like to assume.

There's a school science lesson called 'clay boats.' I don't have any clay, but I made boats out of aluminum foil. I took a small piece and a large piece that I folded up to a small size. I wrapped them each around a little cup, to make 2 boats of the same size, but one weighed less than the other. When I put the 2 boats in a glass of water, I could see that the heavier boat, from the folded-up piece of aluminum foil, sank lower in the water. That reminded me that a boat will sink into the water deep enough to displace a weight of water equal to the weight of the boat.

It's fun to see how many pennies you can put in your toy boat before it sinks. Maybe I'll try that with my 2 boats!

It doesn't, really. Your boat floats if the boat plus all of its contents are lighter than the liquid (i.e. water) that your boat is floating in. The type of material affects its density and thus the amount of cargo it can hold for a given design, but you can make a boat out of anything that doesn't actively dissolve in the fluid in which it is floating (a boat made of sugar will not float for long...).

The denser the material, the harder it is to make the boat float. By density, we mean that there is more "stuff" in the same volume.

For example, if we look at a steel ball and a cotton ball of the same size, so the steel ball would be heavier than the cotton ball even though the balls take up the same amount of space. This is because steel is denser than cotton. Now, what is the principle that makes boats float? To understand it, we have to talk about buoyancy - something can be buoyant in water if and only if the water it "pushes away" (displaces) weighs more than the part that is under the water. Empty plastic water bottles will float because the plastic and the air in it, together, is lighter than the water the bottle displaces. If we fill this empty water bottle with rocks, however, it will sink because the bottle now weighs more than the amount of water it displaces.

Now if we consider a small boat, the part that would be submerged in water, including the air in the boat itself, needs to weigh less than the water it pushes away, and it is easier to make the boat weigh less if we make the boat out of less dense materials such as wood, and not steel.