What makes a steel ship float?

Question

what allows a metal ship such as a cruise ship or military ship to float? what is used as ballast that allows a massive metal object to float on water?

Answer 1

The metal is heavy but the air inside is lite . the ships size and shape displaces water till the amount of water weighs the same as the metal and the air. They have even made boats out of concrete

Answer 2

The ship weighs less than the amount of water it displaces,i think ship and subs used water as ballast.

Answer 3

A boat stays afloat because its weight is equal to that of the water it displaces. The material of the boat itself may be heavier than water (per volume), but it forms only the outer layer. Inside it is air, which is negligible in weight. But it does add to the volume. The central term here is density, which is mass ('weight') per volume. The mass of the boat (plus contents) as a whole has to be divided by the volume below the waterline. If the boat floats, then that is equal to the density of water. If weight is added to the boat, the volume below the waterline will have to increase too, to keep the mass/weight balance equal, so the boat sinks a little to compensate.

Ballast which when added lowers the center of gravity and can make a vessel more stable.  Ballast can be anything, but is normally lead, or in some wake boarding boats today they are using water bags. This increases the wake of the boat - making a good surface for the wake boarded to enjoy.  Too much ballast would cause the vessel to displace too much water - and sink.

Answer 4

yes its displacement. since the ships hull is mostly full of air, it weighs less than the amount of water which it displaced.

Answer 5

The standard definition of floating was first recorded by Archimedes and goes something like this: An object in a fluid experiences an upward force equal to the weight of the fluid displaced by the object. So if a boat weighs 1,000 pounds (or kilograms), it will sink into the water until it has displaced 1,000 pounds (or kilograms) of water. Provided that the boat displaces 1,000 pounds of water before the whole thing is submerged, the boat floats.

It is not very hard to shape a boat in such a way that the weight of the boat has been displaced before the boat is completely underwater. The reason it is so easy is that a good portion of the interior of any boat is air (unlike a cube of steel, which is solid steel throughout). The average density of a boat -- the combination of the steel and the air -- is very light compared to the average density of water. So very little of the boat actually has to submerge into the water before it has displaced the weight of the boat.

A boat's average density is light compared to water's average density.

The next question to ask involves floating itself. How do the water molecules know when 1,000 pounds of them have gotten out of the way? It turns out that the actual act of floating has to do with pressure rather than weight. If you take a column of water 1 inch square and 1 foot tall, it weighs about 0.44 pounds depending on the temperature of the water (if you take a column of water 1 cm square by 1 meter tall, it weights about 100 grams). That means that a 1-foot-high column of water exerts 0.44 pounds per square inch (psi). Similarly, a 1-meter-high column of water exerts 9,800 pascals (Pa).

If you were to submerge a box with a pressure gauge attached (as shown in this picture) into water, then the pressure gauge would measure the pressure of the water at the submerged depth:

you were to submerge the box 1 foot into the water, the gauge would read 0.44 psi (if you submerged it 1 meter, it would read 9,800 Pa). What this means is that the bottom of the box has an upward force being applied to it by that pressure. So if the box is 1 foot square and it is submerged 1 foot, the bottom of the box is being pushed up by a water pressure of (12 inches * 12 inches * 0.44 psi) 62 pounds (if the box is 1 meter square and submerged 1 meter deep, the upward force is 9,800 newtons). This just happens to exactly equal the weight of the cubic foot or cubic meter of water that is displaced!

It is this upward water pressure pushing on the bottom of the boat that is causing the boat to float. Each square inch (or square centimeter) of the boat that is underwater has water pressure pushing it upward, and this combined pressure floats the boat.

http://www.howstuffworks.com/question254...

Answer 6

It has nothing to do with the air inside, just the displacement of water. To prove this to yourself, take a lightbulb and put it in water. The lightbulb has no air inside (by definition, the inside of a lightbulb is a near-vacuum), but it floats even though it is made of glass and aluminum, both of which are heavier than water. Once you've proved this one to yourself and can dispense with the "air" thing, take a ceramic or glass cereal bowl, and float it in your bathtub. Then fill it with water and watch it sink, to prove to yourself that the glass or ceramic is not inherently buoyant. Then empty it and float it again.

What is happening is that the bowl is pushing a certain volume of water away. That volume is exactly equal to the weight of the bowl. This is what we mean by "displacement". A steel (or aluminum, or ferro-cement, or whatever) hulled ship works in exactly the same way. A wooden-hulled ship also works in exactly the same way, but because wooden-hulled ships evolved out of dugout canoes, which in turn evolved out of logs which were inherently buoyant, it took the world a really long time to figure out that ship hulls didn't need to be made out of buoyant materials. But they can be.

Answer 7

ummm - a sunken ship displaces water too.

Maybe it is the buoyancy - the force of water pushing up that makes a boat float.  ahhh - nah what do I know.