how does a cruise ship float?

Answer 1

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.

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 one inch square and a foot tall, it weighs about 0.44 pounds depending on the temperature of the water (If you take a column of water one cm square by a meter tall, it weights about 100 grams). That means that a foot-high column of water exerts 0.44 PSI (Pounds per Square Inch). Similarly a meter high column of water exerts 9,800 Pascals.

If you were to submerge a box with a pressure gauge attached into water, then the pressure gauge would measure the pressure of the water at the submerged depth:

If you submerged the box into the water one foot, the gauge would read 0.44 PSI (if you submerged it one 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 one foot square and it is submerged one 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 one meter square and submerged one 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.

Answer 2

The key to floating is that the object must displace an amount of water which is equal to its own weight.

For example, suppose you had a block of wood that was 1 foot square. Let's say that this block of wood weighs about 50 pounds. Now say we lower that wood into the water. The wood will move down into the water until it has displaced 50 pounds of water. That means that fifty pounds of water are pushing back up on the block and making it float.

The weight of the ship pushes down, the displaced water pushes up.

On a large ship like an ocean liner or tanker, the movement of one person doesn't affect the stability of the ship because it was designed to safely carry lots of weight. But on a small boat, like a fishing boat, your weight and the weight of your gear (and where you put it) has an effect on the stability of the boat.

Answer 3

All the airpockets they biuld in the lower decks of the ship

Here is a more educated answer:
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.

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 one inch square and a foot tall, it weighs about 0.44 pounds depending on the temperature of the water (If you take a column of water one cm square by a meter tall, it weights about 100 grams). That means that a foot-high column of water exerts 0.44 PSI (Pounds per Square Inch). Similarly a meter high column of water exerts 9,800 Pascals.

If you were to submerge a box with a pressure gauge attached into water, then the pressure gauge would measure the pressure of the water at the submerged depth:

If you submerged the box into the water one foot, the gauge would read 0.44 PSI (if you submerged it one 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 one foot square and it is submerged one 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 one meter square and submerged one 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://home.g-net.net/~cbrock/OddsEnds.htm

Hope this answers your question :)

Answer 4

The weight of the ship is less than the weight of water that is the same mass as the ship. This is how anything floats rather than sinks.

Answer 5

For a really easy to understand answer of your question about why a cruise ship floats, check out this website
http://www.suzy.co.nz/suzysworld/Factpage.asp?FactSheet=90

Answer 6

floating depends on bouyancy. For something to be bouyant, it has to displace more water than it weighs. So, you take the weight of the cruise ship and compare that to the volume of the submerged hull and you get your answer.

Answer 7

the way the ship is made.......there are ait pockets that keep the big boy afloat.........the lower decks serve as the inside of a balloon per-say and the ship being the actual balloon .

Answer 8

Displacement.

Answer 9

Buoyancy due to air trapped in ballast tanks.

Answer 10

On water. When it is in drydock it is just hanging there.