How to calculate the amount of water or air to make the submarine sink or float to a certain depth?

Question

ps: please give me the method cos i nid it 4 my project wrk..............

Answer 1

It is an interesting question, and I saw it demonstrated just a few days ago with a plastic soda bottle filled with water.  You put some water in an eye dropper and drop the eye dropper into the soda bottle.  Put the lid back on the soda bottle, and squeeze the bottle.  The eye dropper will move up and down in the bottle.  Very neat to see.   Here are a couple of links that may help you.

Answer 2

For all practical purposes, the density of water (or seawater) is constant with depth.  you cannot just open a valve and have the boat submerge to a predetermined depth.  

you need to lose bouyancy, sink to the proper depth, then add air to obtain "neutral" bouyancy.  This is not a static situation.  small fluctuations will cause the boat (or fish) to either sink or rise.

In modern submersibles, the control system stablilizes the depth by controlling the volume of air in its tanks.  if there is too much and the boat creeps upwards, it stores some in compressed air tanks (doesnt waste it) and the boat will stop rising.  

if it starts creeping downward, some air is taken from compressed tanks and let into the main tanks.

Answer 3

You need to know the weight and displacement of the sub. Then it's a simple calc using the weights of water and air relative to gravity and the specific gravity of the water the sub is travelling in.